Over 10.000 scientific papers have been published by members of the Materials Chain since the foundation of the University Alliance Ruhr in 2010. This tremendous output is proof of the excellent environment the Ruhr Area provides for research in the field of materials science and technology.
Below, you can either scroll through the complete list of our annually published material, or search for a specific author or term via the free text search to get to know our research strengths. You can also review the publication record of every Materials Chain member via his or her personal member’s page.
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2022 • 415 A mechanically strong and ductile soft magnet with extremely low coercivity
Han, L. and Maccari, F. and Souza Filho, I.R. and Peter, N.J. and Wei, Y. and Gault, B. and Gutfleisch, O. and Li, Z. and Raabe, D.
Nature 608 310-316 (2022)Soft magnetic materials (SMMs) serve in electrical applications and sustainable energy supply, allowing magnetic flux variation in response to changes in applied magnetic field, at low energy loss1. The electrification of transport, households and manufacturing leads to an increase in energy consumption owing to hysteresis losses2. Therefore, minimizing coercivity, which scales these losses, is crucial3. Yet meeting this target alone is not enough: SMMs in electrical engines must withstand severe mechanical loads; that is, the alloys need high strength and ductility4. This is a fundamental design challenge, as most methods that enhance strength introduce stress fields that can pin magnetic domains, thus increasing coercivity and hysteresis losses5. Here we introduce an approach to overcome this dilemma. We have designed a Fe–Co–Ni–Ta–Al multicomponent alloy (MCA) with ferromagnetic matrix and paramagnetic coherent nanoparticles (about 91 nm in size and around 55% volume fraction). They impede dislocation motion, enhancing strength and ductility. Their small size, low coherency stress and small magnetostatic energy create an interaction volume below the magnetic domain wall width, leading to minimal domain wall pinning, thus maintaining the soft magnetic properties. The alloy has a tensile strength of 1,336 MPa at 54% tensile elongation, extremely low coercivity of 78 A m−1 (less than 1 Oe), moderate saturation magnetization of 100 A m2 kg−1 and high electrical resistivity of 103 μΩ cm. © 2022, The Author(s).
view abstract doi: 10.1038/s41586-022-04935-3 2022 • 414 Automated and manual classification of metallic nanoparticles with respect to size and shape by analysis of scanning electron micrographs [Automatisierte und manuelle Klassifizierung metallischer Nanopartikel nach Größe und Form aus rasterelektronenmikroskopischen Aufnahmen]
Bals, J. and Loza, K. and Epple, P. and Kircher, T. and Epple, M.
Materialwissenschaft und Werkstofftechnik 53 270-283 (2022)Automated image analysis has been applied to scanning electron micrographs (transmission mode; STEM) of metallic nanoparticles (silver and gold; about 10 nm to 20 nm). For a reliable particle identification, scanning electron microscopic images must be recorded with distinct contrast and resolution parameters. The particles were separated from the background and classified according to shape and size by machine learning (machine learning). Training images were created with model particles cut out of real electron microscopic images. The automated analysis of the particle size (expressed as area) was well possible, but overlapping particles could not be safely separated. The assignment of particle to six different shape classes (sphere, triangle, square, pentagon, hexagon, rod) by automated analysis was difficult. The fact that real particles never have an ideal geometrical shape but are always distorted or have rough edges or cropped tips is the fundamental reason of this problem. This effect also occurred with human image evaluators and poses a considerable obstacle in the training process for machine learning. Image analysis by machine learning techniques is difficult if different human evaluators disagree on the shape assignment of given particles because a proper training cannot be provided. © 2022 The Authors. Materialwissenschaft und Werkstofftechnik published by Wiley-VCH GmbH.
view abstract doi: 10.1002/mawe.202100285 2022 • 413 Boron in Ni-Rich NCM811 Cathode Material: Impact on Atomic and Microscale Properties
Roitzheim, C. and Kuo, L.-Y. and Sohn, Y.J. and Finsterbusch, M. and Möller, S. and Sebold, D. and Valencia, H. and Meledina, M. and Mayer, J. and Breuer, U. and Kaghazchi, P. and Guillon, O. and Fattakhova-Rohlfing, D.
ACS Applied Energy Materials 5 524-538 (2022)Doping of Ni-rich cathode active materials with boron is a promising way to improve their cycling stability and mitigate their degradation, but it is still not understood how this effect is achieved and where the boron is located. To receive deeper insights into the impact of doping on atomic and microscale properties, B-doped Li[Ni0.8Co0.1Mn0.1]O2 (NCM811) cathode materials were synthesized by a hydroxide coprecipitation as a model compound to verify the presence and location of boron in B-doped, Ni-rich NCM, as well as its impact on the microstructure and electrochemical properties, by a combined experimental and theoretical approach. Besides X-ray diffraction and Rietveld refinement, DFT calculation was used to find the preferred site of boron absorption and its effect on the NCM lattice parameters. It is found that boron shows a trigonal planar and tetrahedral coordination to oxygen in the Ni layers, leading to a slight increase in lattice parameter c through an electrostatic interaction with Li ions. Therefore, B-doping of NCM811 affects the crystal structure and cation disorder and leads to a change in primary particle size and shape. To experimentally prove that the observations are caused by boron incorporated into the NCM lattice, we detected, quantified, and localized boron in 2 mol % B-doped NCM811 by ion beam analysis and TOF-SIMS. It was possible to quantify boron by NRA with a depth resolution of 2 μm. We found a boron enrichment on the agglomerate surface but also, more importantly, a significant high and constant boron concentration in the interior of the primary particles near the surface, which experimentally verifies that boron is incorporated into the NCM811 lattice. ©
view abstract doi: 10.1021/acsaem.1c03000 2022 • 412 Determining the sintering kinetics of Fe and FexOy-Nanoparticles in a well-defined model flow reactor
Rosenberger, T. and Skenderović, I. and Sellmann, J. and Wollny, P. and Levish, A. and Wlokas, I. and Kempf, A. and Winterer, M. and Kruis, F.E.
Aerosol Science and Technology 56 833-846 (2022)A model flow reactor provides a narrow particle temperature-residence time distribution with well-defined conditions and is mandatory to measure changes of the particle structure precisely. The experimental data of iron and iron oxide agglomerates are used to determine the sintering kinetics considering the temperature-time history of the particles. Thousand particle trajectories are tracked in a validated CFD model at three different furnace temperatures each. Strongly agglomerated particles with a small primary particle size (∼4 nm) are synthesized by spark discharge and are size-selected (25–250 nm) before sintering. The structure development is measured simultaneously with different online instrumentations and the structure calculated by means of structure models. A simple sintering model, based on the reduction of surface energy, is numerically quantified with the experimental results. The surface of the particles is strongly dependent on the primary particle size and the agglomerate structure. The chemical phase is analyzed using the offline techniques XANES, XRD, and EELS. It is observed that the addition of hydrogen led to a reduction of iron oxide to iron nanoparticles and to changes of the sintering kinetics. The sintering exponent (Formula presented.) = 1 was found to be optimal. For Fe, an activation energy (Formula presented.) of 59.15 kJ/mol and a pre-exponential factor (Formula presented.) of 1.57 104 s/m were found, for Fe3O4 an activation energy (Formula presented.) of 55.22 kJ/mol and a pre-exponential factor (Formula presented.) of 2.54 104 s/m. Copyright © 2022 American Association for Aerosol Research. © 2022 American Association for Aerosol Research.
view abstract doi: 10.1080/02786826.2022.2089011 2022 • 411 Effects of Extracellular Vesicles from Osteogenic Differentiated Human BMSCs on Osteogenic and Adipogenic Differentiation Capacity of Naïve Human BMSCs
Wang, C. and Stöckl, S. and Li, S. and Herrmann, M. and Lukas, C. and Reinders, Y. and Sickmann, A. and Grässel, S.
Cells 11 (2022)Osteoporosis, or steroid-induced osteonecrosis of the hip, is accompanied by increased bone marrow adipogenesis. Such a disorder of adipogenic/osteogenic differentiation, affecting bone-marrow-derived mesenchymal stem cells (BMSCs), contributes to bone loss during aging. Here, we investigated the effects of extracellular vesicles (EVs) isolated from human (h)BMSCs during different stages of osteogenic differentiation on the osteogenic and adipogenic differentiation capacity of naïve (undifferentiated) hBMSCs. We observed that all EV groups increased viability and proliferation capacity and suppressed the apoptosis of naïve hBMSCs. In particular, EVs derived from hBMSCs at late-stage osteogenic differentiation promoted the osteogenic potential of naïve hBMSCs more effectively than EVs derived from naïve hBMSCs (naïve EVs), as indicated by the increased gene expression of COL1A1 and OPN. In contrast, the adipogenic differentiation capacity of naïve hBMSCs was inhibited by treatment with EVs from osteogenic differentiated hBMSCs. Proteomic analysis revealed that osteogenic EVs and naïve EVs contained distinct protein profiles, with pro-osteogenic and anti-adipogenic proteins encapsulated in osteogenic EVs. We speculate that osteogenic EVs could serve as an intercellular communication system between bone- and bone-marrow adipose tissue, for transporting osteogenic factors and thus favoring pro-osteogenic processes. Our data may support the theory of an endocrine circuit with the skeleton functioning as a ductless gland. © 2022 by the authors.
view abstract doi: 10.3390/cells11162491 2022 • 410 Experimental and computational analysis of the coolant distribution considering the viscosity of the cutting fluid during machining with helical deep hole drills
Oezkaya, E. and Michel, S. and Biermann, D.
Advances in Manufacturing (2022)An experimental analysis regarding the distribution of the cutting fluid is very difficult due to the inaccessibility of the contact zone within the bore hole. Therefore, suitable simulation models are necessary to evaluate new tool designs and optimize drilling processes. In this paper the coolant distribution during helical deep hole drilling is analyzed with high-speed microscopy. Micro particles are added to the cutting fluid circuit by a developed high-pressure mixing vessel. After the evaluation of suitable particle size, particle concentration and coolant pressure, a computational fluid dynamics (CFD) simulation is validated with the experimental results. The comparison shows a very good model quality with a marginal difference for the flow velocity of 1.57% between simulation and experiment. The simulation considers the kinematic viscosity of the fluid. The results show that the fluid velocity in the chip flutes is low compared to the fluid velocity at the exit of the coolant channels of the tool and drops even further between the guide chamfers. The flow velocity and the flow pressure directly at the cutting edge decrease to such an extent that the fluid cannot generate a sufficient cooling or lubrication. With the CFD simulation a deeper understanding of the behavior and interactions of the cutting fluid is achieved. Based on these results further research activities to improve the coolant supply can be carried out with great potential to evaluate new tool geometries and optimize the machining process. © 2022, The Author(s).
view abstract doi: 10.1007/s40436-021-00383-w 2022 • 409 Green Textile Materials for Surface Enhanced Raman Spectroscopy Identification of Pesticides Using a Raman Handheld Spectrometer for In-Field Detection
Hermsen, A. and Schoettl, J. and Hertel, F. and Cerullo, M. and Schlueter, A. and Lehmann, C.W. and Mayer, C. and Jaeger, M.
Applied Spectroscopy 76 1222-1233 (2022)Surface enhanced Raman spectroscopy (SERS) has evolved into a powerful analytical method in food and environmental analytical sciences due to its high sensitivity. Pesticide analysis is a major discipline therein. Using sustainable materials has become increasingly important to adhere to Green Chemistry principles. Hence, the green textiles poly-(L-lactic acid) (PLA) and the mixed fabric polyethylene terephthalate polyamide (PET/PA) were investigated for their applicability as solid supports for gold nanoparticles to yield SERS substrates. Gold nanoparticle solutions and green textile supports were prepared after preparation optimization. Particle size, dispersity, and particle distribution over the textiles were characterized by absorption spectroscopy and transmission electron imaging. The performance of the SERS substrates was tested using the three pesticides imidacloprid, paraquat, and thiram and a handheld Raman spectrometer with a laser wavelength of 785 nm. The resulting SERS spectra possessed an intra-substrate variation of 7–8% in terms of the residual standard deviation. The inter-substrate variations amounted to 15% for PET/PA and to 27% for PLA. Substrate background signals were smaller with PLA but more enhanced through PET/PA. The pesticides could be detected at 1 pg on PET/PA and at 3 ng on PLA. Hence, PET/PA woven textile soaked with gold nanoparticle solution provides green SERS substrates and might prove, in combination with fieldable Raman spectrometers, suitable for in-field analytics for pesticide identification. © The Author(s) 2022.
view abstract doi: 10.1177/00037028221097130 2022 • 408 Hansen parameter evaluation for the characterization of titania photocatalysts using particle size distributions and combinatorics
Anwar, O. and Bapat, S. and Ahmed, J. and Xie, X. and Sun, J. and Segets, D.
Nanoscale 14 13593-13607 (2022)Titania photocatalysts have great potential as remediators of air pollution. Although various aspects of photocatalyst synthesis, adsorption and photoactivity have been investigated, a thorough understanding of the particle surface behavior has not yet been fully realized. In order to learn more about the principles behind the surface behavior, we investigate the Hansen solubility/similarity parameters (HSPs) for analyzing and evaluating three photocatalysts synthesized by the gas phase method, solvothermal reaction and sol-gel method, respectively. A particle size distribution-based categorization scheme is introduced for characterizing each material's Hansen parameters based on its interaction with a list of selected probe liquids. The latter was deduced from particle size distributions assessed by analytical centrifugation. Subsequent comparison of the Hansen parameters of the investigated materials shows how HSPs can potentially be used as a model for predicting the pollutant adsorption behavior on the photocatalyst surface. This serves as a first step in heading towards an improved understanding of the particle behavior and translating it into a knowledge-based design, i.e., synthesis and hybridization of novel photocatalysts. © 2022 The Royal Society of Chemistry.
view abstract doi: 10.1039/d2nr02711a 2022 • 407 Hydrogen trapping and embrittlement in high-strength Al alloys
Zhao, H. and Chakraborty, P. and Ponge, D. and Hickel, T. and Sun, B. and Wu, C.-H. and Gault, B. and Raabe, D.
Nature 602 437-441 (2022)Ever more stringent regulations on greenhouse gas emissions from transportation motivate efforts to revisit materials used for vehicles1. High-strength aluminium alloys often used in aircrafts could help reduce the weight of automobiles, but are susceptible to environmental degradation2,3. Hydrogen ‘embrittlement’ is often indicated as the main culprit4; however, the exact mechanisms underpinning failure are not precisely known: atomic-scale analysis of H inside an alloy remains a challenge, and this prevents deploying alloy design strategies to enhance the durability of the materials. Here we performed near-atomic-scale analysis of H trapped in second-phase particles and at grain boundaries in a high-strength 7xxx Al alloy. We used these observations to guide atomistic ab initio calculations, which show that the co-segregation of alloying elements and H favours grain boundary decohesion, and the strong partitioning of H into the second-phase particles removes solute H from the matrix, hence preventing H embrittlement. Our insights further advance the mechanistic understanding of H-assisted embrittlement in Al alloys, emphasizing the role of H traps in minimizing cracking and guiding new alloy design. © 2022, The Author(s).
view abstract doi: 10.1038/s41586-021-04343-z 2022 • 406 LES of nanoparticle synthesis in the spraysyn burner: A comparison against experiments
Sellmann, J. and Wollny, P. and Baik, S.-J. and Suleiman, S. and Schneider, F. and Schulz, C. and Wiggers, H. and Wlokas, I. and Kempf, A.M.
Powder Technology 404 (2022)The synthesis of iron oxide nanoparticles from iron nitrate in the SpraySyn spray flame reactor was investigated by experiment and simulation. The focus was on the spray and flame structure, the particle growth by nucleation and coagulation, and the unresolved effects and their impact on the dispersed phase. The reacting flow was modeled in large eddy simulations with the premixed flamelet generated manifolds technique, including modifications for aerosol nucleation. Particle dynamics were described with a sectional model and a subgrid scale coagulation kernel. The particle size distributions at different distances from the burner surface were obtained using a particle mass spectrometer. The experiments and simulations are in good agreement for the flame centreline velocity and both size distribution and mean size of the particles (for particles larger 1 nm - the approximate detection limit of the experiment). Furthermore, simulations enabled to interpret the temporal evolution of the particle size distribution. © 2022 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2022.117466 2022 • 405 Manufacturing of W/steel composites using electro-discharge sintering process
Ganesh, V. and Leich, L. and Dorow-Gerspach, D. and Heuer, S. and Coenen, J.W. and Wirtz, M. and Pintsuk, G. and Gormann, F. and Lied, P. and Baumgärtner, S. and Theisen, W. and Linsmeier, C.
Nuclear Materials and Energy 30 (2022)Tungsten-steel metal matrix composites are consolidated using electro-discharge sintering. At first steel and tungsten powders are sintered separately and then 25 vol% W, 50 vol% W and 75 vol% W mixed powders are sintered. A thorough process parametric study is carried out involving analysis of the influence of particle size distribution, sintering pressure, and discharge energy on the maximum discharge current and obtained residual porosity. Thermal expansion coefficient and the specific heat capacity of the optimized sintered composites are almost same as their theoretical values, however the thermal conductivities and the mechanical properties are lower than the expected values. © 2021 The Authors
view abstract doi: 10.1016/j.nme.2021.101089 2022 • 404 NdFeB Magnets with Well-Pronounced Anisotropic Magnetic Properties Made by Electric Current-Assisted Sintering
Prasad Mishra, T. and Leich, L. and Krengel, M. and Weber, S. and Röttger, A. and Bram, M.
Advanced Engineering Materials (2022)Electric current-assisted sintering (ECAS) technologies are highly promising for processing of NdFeB magnets. Due to the combination of direct Joule heating and application of external load, even powders, whose particle size distribution and morphology are not optimum for conventional powder processing like melt-spun powders or magnet scrap, can be easily sintered to high densities. A systematic study is done to demonstrate the potential of field-assisted sintering technique/spark plasma sintering (FAST/SPS) and flash spark plasma sintering (flash SPS) for sintering of NdFeB powders. Melt-spun, commercial NdFeB powder (Magnequench MQU-F) is used as starting material. Its platelet-like shape makes this powder extremely difficult to sinter by conventional methods. This study clearly reveals that especially in the case of flash SPS application of external pressure in combination with short cycle times enables to achieve well-pronounced anisotropic magnetic properties without the need of subsequent upset forging. Optimized flash SPS parameters are applied to NdFeB magnet scrap with broad particle size distribution, demonstrating the general potential of ECAS technologies for recycling of waste magnet materials. Finally, the results are benchmarked with respect to established NdFeB processing technologies and electrodischarge sintering (EDS), another promising ECAS technology with very short cycling time. © 2022 The Authors. Advanced Engineering Materials published by Wiley-VCH GmbH.
view abstract doi: 10.1002/adem.202201027 2022 • 403 Particle Generation with Liquid Carbon Dioxide Emulsions
Lauscher, C. and Schaldach, G. and Thommes, M.
Chemical Engineering and Technology 45 1631-1636 (2022)Spray drying is a common technique for particle generation. However, due to limitations in the droplet size, the production of solid submicron particles using conventional atomizers has proven to be challenging. With the aim of overcoming this limitation, the generation and expansion of emulsions of an aqueous solution and liquid carbon dioxide with a subsequent drying step was investigated. Potassium chloride concentrations in the solution between 0.1 and 10 wt. % and mass loads of the aqueous disperse phase between 0.01 and 0.09 were used in order to study their impact on the droplet and particle size. For the lowest potassium chloride concentration, median particle diameters in the submicron size range were measured for all mass loads of the disperse phase. © 2022 The Authors. Chemical Engineering Technology published by Wiley-VCH GmbH.
view abstract doi: 10.1002/ceat.202200176 2022 • 402 Predicting Throughput and Melt Temperature in Pharmaceutical Hot Melt Extrusion
Gottschalk, T. and Özbay, C. and Feuerbach, T. and Thommes, M.
Pharmaceutics 14 (2022)Even though hot melt extrusion (HME) is a commonly applied process in the pharmaceutical area, determination of the optimal process parameters is demanding. The goal of this study was to find a rational approach for predetermining suitable extrusion parameters, with a focus on material temperature and throughput. A two-step optimization procedure, called scale-independent optimization strategy (SIOS), was applied and developed further, including the use of an autogenic extrusion mode. Three different polymers (Plasdone S-630, Soluplus, and Eudragit EPO) were considered, and different optimal process parameters were assessed. The maximum barrel load was dependent on the polymers’ bulk density and the extruder size. The melt temperature was influenced by the screw speed and the rheological behavior of the polymer. The melt viscosity depended mainly on the screw speed and was self-adjusted in the autogenic extrusion. A new approach, called SIOS 2.0, was suggested for calculating the extrusion process parameters (screw speed, melt temperature and throughput) based on the material data and a few extrusion experiments. © 2022 by the authors.
view abstract doi: 10.3390/pharmaceutics14091757 2022 • 401 Rejuvenation in Deep Thermal Cycling of a Generic Model Glass: A Study of Per-Particle Energy Distribution
Bruns, M. and Varnik, F.
Materials 15 (2022)We investigate the effect of low temperature (cryogenic) thermal cycling on a generic model glass and observe signature of rejuvenation in terms of per-particle potential energy distributions. Most importantly, these distributions become broader and its average values successively increase when applying consecutive thermal cycles. We show that linear dimension plays a key role for these effects to become visible, since we do only observe a weak effect for a cubic system of roughly one hundred particle diameter but observe strong changes for a rule-type geometry with the longest length being two thousand particle diameters. A consistent interpretation of this new finding is provided in terms of a competition between relaxation processes, which are inherent to glassy systems, and excitation due to thermal treatment. In line with our previous report (Bruns et al., PRR 3, 013234 (2021)), it is shown that, depending on the parameters of thermal cycling, rejuvenation can be either too weak to be detected or strong enough for a clear observation. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
view abstract doi: 10.3390/ma15030829 2022 • 400 Resolving particle shape in DEM simulations from tabulated geometry information
Deshpande, R. and Mahiques, E. and Wirtz, S. and Scherer, V.
Powder Technology 407 (2022)DEM applications require versatile representations of the particle shapes. The downside of resolved shapes is the required computational effort. In this short communication, we propose new measures to reduce the computational effort needed to evaluate the pairwise contact of resolved polytopes in DEM simulations. Employing the Gilbert–Johnson–Keerthi (GJK) and Expanding Polytope algorithm (EPA) algorithm it is demonstrated that restricting the particle vertices to the actually required ones, which can be obtained from a directional tabulation prior to the simulation, reduces the computational effort drastically. The feasibility of this strategy is evaluated and discussed. Applicability is demonstrated by comparing the simulated granular outflow of regular polyhedrons with differently resolved edges from a hopper with experimental data. The results obtained disclose the strong effect of geometric features on particle discharge. © 2022 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2022.117700 2022 • 399 Robust optimization in nanoparticle technology: A proof of principle by quantum dot growth in a residence time reactor
Dienstbier, J. and Aigner, K.-M. and Rolfes, J. and Peukert, W. and Segets, D. and Pflug, L. and Liers, F.
Computers and Chemical Engineering 157 (2022)Knowledge-based determination of the best-possible experimental setups for nanoparticle design is highly challenging. Additionally, such processes are accompanied by noticeable uncertainties. Therefore, protection against those is needed. Robust optimization helps determining optimal processes. The latter guarantees quality requirements regardless of how uncertainties e.g., in raw materials, particle size distributions (PSD), heat and mass transport characteristics, and (growth) rates, manifest within predefined ranges. To approach this task, we exemplarily model a particle synthesis process with seeded growth by population balance equations and study different growth kinetics. We determine the mean residence time maximizing the product mass subject to a guaranteed yield. Additionally, we hedge against uncertain growth rates and derive an algorithmically tractable reformulation for the robustified problem. This reformulation can be applied if both the objective and the constraint functions are quasiconcave in the uncertainty which is a natural assumption in this context. We also show that the approach extends to higher-dimensional uncertainties if the uncertain parameters do not influence each other. We evaluate our approach for seeded growth synthesis of zinc oxide quantum dots and demonstrate computationally that a guaranteed yield is met for all growth rates within predefined regions. The protection against uncertainties only reduces the maximum amount of product that can be obtained by a negligible margin. © 2021
view abstract doi: 10.1016/j.compchemeng.2021.107618 2022 • 398 Transient uptake measurements with a physisorption instrument: Trends in gas-phase diffusivities within mesoporous materials
Joshi, H. and Hopf, A. and Losch, P. and Schmidt, W. and Schüth, F.
Microporous and Mesoporous Materials 330 (2022)The measurement of diffusivity within porous solids is vital for the characterization of materials, especially in heterogeneous catalysis and separation processes. Numerous methods have been developed to measure gas-phase diffusivities within materials. However, establishing correlations between the diffusivities and the properties of a material is challenging. Herein, we report a method for obtaining trends in gas-phase diffusivity of N2 at 77 K within three different sets of mesoporous materials, disordered, ordered silica, and carbons-based materials. Synthesis procedures are reproducible and controlled precisely to achieve monodisperse particle size and defined pore size distributions. A standard physisorption device, Micromeritics 3Flex, is used to obtain the required transient data. These two aspects offer a suitable database of materials to identify trends and reduce the challenges associated with obtaining experimental data. A simplified model is fitted over the transient data with MATLAB to obtain empirical diffusivities used for trend analysis. The trends are based on a constant Dτ, an ensemble value representing various diffusion processes occurring during a transient uptake process. The analysis identifies several correlations between the diffusivity and properties of materials, such as type of pore structure, pore size, and the chemical nature of the material. Based on the principles reported, this study can be extended to other adsorptive molecules or different temperatures. The possibility of using standard sorption instrumentation will allow a broader user community to employ the reported methodology. © 2021 Elsevier Inc.
view abstract doi: 10.1016/j.micromeso.2021.111627 2021 • 397 Adjoint-based sensitivity analysis of char combustion surface reaction kinetics
Hassan, A. and Sayadi, T. and Schiemann, M. and Scherer, V.
Fuel 287 (2021)Simulations of solid particle combustion rely on models to approximate the reactions on the surface of the particle and in the surrounding gas. These models, in turn, depend on many model parameters, which are determined, most commonly, by experiments and contain a certain level of uncertainty. It is therefore essential to correctly determine the sensitivities of measured quantities of interest, with respect to the existing model parameters. This study, concentrates on a one-step model describing the heterogeneous reaction on the surface of a char particle, and in particular, the surface model presented by Schiemann et al. . Adjoint-based methods are then employed to extract sensitivities of various quantities of interests, including the burning rate and total heat release, with respect to surface model parameters, such as, the activation energy, and the pre-exponential factor. The variation of these sensitivities are then assessed as the particle size and free stream composition are varied. © 2020 Elsevier Ltd
view abstract doi: 10.1016/j.fuel.2020.119503 2021 • 396 Analysis of wood pellet degradation characteristics based on single particle impact tests
Jägers, J. and Spatz, P. and Wirtz, S. and Scherer, V.
Powder Technology 378 704-715 (2021)The knowledge of size reduction of wood pellets during pneumatic conveying is important to achieve failure-free system operation and to set-up adequate quality assurance processes. In the present study, experiments are performed with a single particle impact test facility. A stereoscopic high-speed camera set allows 3D-particle tracking and visual analysis of the particles' degradation properties. Based on the data obtained, empirical correlations for the statistical description of the pellets' breakage behaviour are presented depending on particle length, impact velocity and collision angle. These relationships are expressed mathematically by two key functions: the so-called selection function (breakage probability) and the breakage function (fragment size distribution). As expected, higher impact velocities lead to more damage, especially at normal collisions (90°) due to the maximum change of momentum. Furthermore, smaller particles tend to be more breakage resistant as they contain less impurities and cracks. Finally, an outlook on the influence of pellet quality and target material on the particles' degradation behaviour is given. Here, pellets with higher durability tend to break at higher impact loads and into larger fragments. In addition, a softer target material (e.g. HDPE) causes less particle breakage than e.g. steel. © 2020 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2020.10.017 2021 • 395 Atmospheric-pressure particle mass spectrometer for investigating particle growth in spray flames
Suleiman, S. and Nanjaiah, M. and Skenderovic, I. and Rosenberger, T. and Kunze, F. and Wlokas, I. and Kruis, F.E. and Wiggers, H. and Schulz, C.
Journal of Aerosol Science 158 (2021)In this work, we introduce a new particle mass spectrometer (AP-PMS) that is able to detect particle-size distributions at ambient pressure using a three-stage pumping design. This device is demonstrated for direct sampling from the particle formation in spray-flame synthesis of iron oxide nanoparticles. Aerosol sampling is performed by a probe with integrated dilution that has been characterized and configured by computational fluid dynamics simulations and the chamber-skimmer system has been investigated by schlieren imaging. The system was validated by detailed characterization of a standardized sooting flame and by iron oxide nanoparticles generated in the SpraySyn burner from iron nitrate dissolved in a mixture of ethanol and 2-ethylhexanoic acid. The PMS results are compared to additional inline measurements with SMPS and ELPI + as well as with TEM measurements of thermophoretically sampled materials from the same location in the spray flame. © 2021 The Authors
view abstract doi: 10.1016/j.jaerosci.2021.105827 2021 • 394 Biodegradable supramolecular micellesviahost-guest interaction of cyclodextrin-terminated polypeptides and adamantane-terminated polycaprolactones
Pottanam Chali, S. and Azhdari, S. and Galstyan, A. and Gröschel, A.H. and Ravoo, B.J.
Chemical Communications 57 9446-9449 (2021)Biodegradable supramolecular micelles were prepared exploiting the host-guest interaction of cyclodextrin and adamantane. Cyclodextrin-initiated polypeptides acted as the hydrophilic corona, whereas adamantane-terminated polycaprolactones served as the hydrophobic core. © The Royal Society of Chemistry 2021.
view abstract doi: 10.1039/d1cc03372g 2021 • 393 Characterizing soot in TEM images using a convolutional neural network
Sipkens, T.A. and Frei, M. and Baldelli, A. and Kirchen, P. and Kruis, F.E. and Rogak, S.N.
Powder Technology 387 313-324 (2021)Soot is an important material with impacts that depend on particle morphology. Transmission electron microscopy (TEM) represents one of the most direct routes to qualitatively assess particle characteristics. However, producing quantitative information requires robust image processing tools, which is complicated by the low image contrast and complex aggregated morphologies characteristic of soot. The current work presents a new convolutional neural network explicitly trained to characterize soot, using pre-classified images of particles from a natural gas engine; a laboratory gas flare; and a marine engine. The results are compared against other existing classifiers before considering the effect that the classifiers have on automated primary particle size methods. Estimates of the overall uncertainties between fully automated approaches of aggregate characterization range from 25% in dp,100 to 85% in DTEM. A consistent correlation is observed between projected-area equivalent diameter and primary particle size across all of the techniques. © 2021 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2021.04.026 2021 • 392 Comparing Direct and Pulsed-Direct Current Electrophoretic Deposition on Neural Electrodes: Deposition Mechanism and Functional Influence
Ramesh, V. and Rehbock, C. and Giera, B. and Karnes, J.J. and Forien, J.-B. and Angelov, S.D. and Schwabe, K. and Krauss, J.K. and Barcikowski, S.
Langmuir 37 9724-9734 (2021)Electrophoretic deposition (EPD) of platinum nanoparticles (PtNPs) on platinum-iridium (Pt-Ir) neural electrode surfaces is a promising strategy to tune the impedance of electrodes implanted for deep brain stimulation in various neurological disorders such as advanced Parkinson's disease and dystonia. However, previous results are contradicting as impedance reduction was observed on flat samples while in three-dimensional (3D) structures, an increase in impedance was observed. Hence, defined correlations between coating properties and impedance are to date not fully understood. In this work, the influence of direct current (DC) and pulsed-DC electric fields on NP deposition is systematically compared and clear correlations between surface coating homogeneity and in vitro impedance are established. The ligand-free NPs were synthesized via pulsed laser processing in liquid, yielding monomodal particle size distributions, verified by analytical disk centrifugation (ADC). Deposits formed were quantified by UV-vis supernatant analysis and further characterized by scanning electron microscopy (SEM) with semiautomated interparticle distance analyses. Our findings reveal that pulsed-DC electric fields yield more ordered surface coatings with a lower abundance of particle assemblates, while DC fields produce coatings with more pronounced aggregation. Impedance measurements further highlight that impedance of the corresponding electrodes is significantly reduced in the case of more ordered coatings realized by pulsed-DC depositions. We attribute this phenomenon to the higher active surface area of the adsorbed NPs in homogeneous coatings and the reduced particle-electrode electrical contact in NP assemblates. These results provide insight for the efficient EPD of bare metal NPs on micron-sized surfaces for biomedical applications in neuroscience and correlate coating homogeneity with in vitro functionality. © 2021 American Chemical Society.
view abstract doi: 10.1021/acs.langmuir.1c01081 2021 • 391 Comprehensive Data Set of Single Particle Combustion under Oxy-fuel Conditions, Part I: Measurement Technique
Vorobiev, N. and Valentiner, S. and Schiemann, M. and Scherer, V.
Combustion Science and Technology 193 2423-2444 (2021)An improved experimental methodology is presented that provides combustion data of single pulverized coal and biomass particles with a high level of detail. This is the first part of a two-article series. A stereoscopic imaging system based on four intensified CCD-cameras is calibrated for in-situ measurements of temperature, size, shape, and velocity of solid fuel particles in the diameter range of 30–300 µm. An elaborate approach for 3D shape reconstruction from orthogonal projections of single particles shows significantly improved accuracy, which is validated against particle samples being collected with a suction probe. The close-meshed combination of imaging pyrometry and shadowgraphy is a further novelty. The parallel application of both techniques provides results for both self-luminous “hot” (imaging pyrometry) and “cold” (shadowgraphy) particles. This enhances information on particle ignition (particles switch from cold to hot) and duration of char burn-out (particles switch from hot to cold). Selected experimental results are presented which demonstrate the informative power of data sets formed by this approach. Torrefied miscanthus is burned in a laminar flow reactor. The particle size and aspect ratio are evaluated for the in-situ measuring method as well as for the collected samples. The results show a good correlation between both analysis routines, indicating the progress in solid fuel characterization by the improved optical technique in combination with particle sampling. © 2020 Taylor & Francis Group, LLC.
view abstract doi: 10.1080/00102202.2020.1743696 2021 • 390 Comprehensive Data Set of Single Particle Combustion under Oxy-fuel Conditions, Part II: Data Set
Vorobiev, N. and Valentiner, S. and Schiemann, M. and Scherer, V.
Combustion Science and Technology 193 2643-2658 (2021)The analysis of the current literature on the subject of detailed single-particle measurements revealed that, despite the fact that numerous experimental investigations are reported, the database for the calibration of predictive burnout models is insufficient. To close this gap, a test rig for the optical investigation of the burning behavior of pulverized fuel particles was put into operation and introduced in the first part of this two-article series. In the second part, the results of a measurement campaign, on a high-volatile bituminous coal, and torrefied Miscanthus in eight oxy-fuel atmospheres are presented. The experimental data contains profiles of particle temperature, size, shape, burnout progress over residence time and, thus, provides a sound basis for the calibration of char burnout models. The combination of chosen optical techniques enables distinguishing between burning and cold particles, the latter being non-ignited or already burnt out. This information is important for the analysis of particle size distributions. In addition to optical measurements, partially reacted solid samples were extracted from the reactor. Besides the proximate and elemental analysis, also the porosity of the samples was determined at several burnout levels. Interestingly, the evolution of particle porosity shows atmosphere-independent trends. © 2020 Taylor & Francis Group, LLC.
view abstract doi: 10.1080/00102202.2020.1754207 2021 • 389 Determination of Particle Size, Core and Shell Size Distributions of Core–Shell Particles by Analytical Ultracentrifugation
Schmidt, T. and Linders, J. and Mayer, C. and Cölfen, H.
Particle and Particle Systems Characterization 38 (2021)In core–shell nanoparticle analysis, the determination of size distributions of the different particle parts is often complicated, especially in liquid media. Density matching is introduced as a method for analyzing core–shell nanoparticles using Analytical Ultracentrifugation (AUC), making it possible to obtain the core size distribution in liquid dispersions. For this approach, the density of the dispersion is adjusted to the density of the shell. Oil filled nanocapsules are utilized with component densities of around 1 g mL−1 to demonstrate this technique. The shell size distribution is calculated supposing the particle size distribution as a convolution of the shell- and core size distributions. Finally, the distributions of core size, shell thickness, particle size, and particle density and thus particle composition are obtained. To clarify the effect of swelling, AUC measurements are combined with further size characterization methods like Particle Tracking Microscopy and Dynamic Light Scattering. © 2021 The Authors. Particle & Particle Systems Characterization published by Wiley-VCH GmbH.
view abstract doi: 10.1002/ppsc.202100079 2021 • 388 FibeR-CNN: Expanding Mask R-CNN to improve image-based fiber analysis
Frei, M. and Kruis, F.E.
Powder Technology 377 974-991 (2021)Fiber-shaped materials (e.g. carbon nano tubes) are of great relevance, due to their unique properties but also the health risk they can impose. Unfortunately, image-based analysis of fibers still involves manual annotation, which is a time-consuming and costly process. We therefore propose the use of region-based convolutional neural networks (R-CNNs) to automate this task. Mask R-CNN, the most widely used R-CNN for semantic segmentation tasks, is prone to errors when it comes to the analysis of fiber-shaped objects. Hence, a new architecture – FibeR-CNN – is introduced and validated. FibeR-CNN combines two established R-CNN architectures (Mask and Keypoint R-CNN) and adds additional network heads for the prediction of fiber widths and lengths. As a result, FibeR-CNN is able to surpass the mean average precision of Mask R-CNN by 33% (11 percentage points) on a novel test data set of fiber images. © 2020 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2020.08.034 2021 • 387 Formation of Co-Au Core-shell nanoparticles with thin gold shells and soft magnetic ϵ?cobalt cores ruled by thermodynamics and kinetics
Johny, J. and Kamp, M. and Prymak, O. and Tymoczko, A. and Wiedwald, U. and Rehbock, C. and Schürmann, U. and Popescu, R. and Gerthsen, D. and Kienle, L. and Shaji, S. and Barcikowski, S.
Journal of Physical Chemistry C 125 9534-9549 (2021)Bimetallic core-shell nanoparticles (CSNPs), where a ferromagnetic core (e.g., Co) is surrounded by a noblemetal thin plasmonic shell (e.g., Au), are highly interesting for applications in biomedicine and catalysis. Chemical synthesis of such structures, however, requires multistep procedures and often suffers from impaired oxidation resistance of the core. Here, we utilized a one-step environmentally friendly laser ablation in liquid technique to fabricate colloidal Co?Au CSNPs with core?shell yields up to 78% in mass. An in-depth analysis of the CSNPs down to single-particle levels revealed the presence of a unique nested core?shell structure with a very thin gold-rich shell, a nanocrystalline ϵ-cobalt sublayer, and a nested gold-rich core. The generated Co?Au CSNPs feature soft magnetic properties, while all gold-rich phases (thin shells and nested cores) exhibit a face-centered cubic solid solution with substantial cobalt substitution. The experimental findings are backed by refined thermodynamic surface energy calculations, which more accurately predict the predominance of solid solution and core?shell phase structures in correlation with particle size and nominal composition. Based on the Co?Au bulk phase diagram and in conjunction with previously reported results on the Fe?Au core?shell system as well as Co? Pt controls, we deduce four general rules for core?shell formation in non-or partially miscible laser-generated bimetallic nanosystems. ©2021 American Chemical Society.
view abstract doi: 10.1021/acs.jpcc.1c02138 2021 • 386 Gd-Ru Nanoparticles Supported on Zr0.5Ce0.5O2Nanorods for Dry Methane Reforming
Das, S. and Sengupta, M. and Bag, A. and Saini, A. and Muhler, M. and Bordoloi, A.
ACS Applied Nano Materials 4 2547-2557 (2021)Dry reforming of methane is considered a potential reaction for the utilization of waste greenhouse gases to generate valuable chemicals. However, catalyst deactivation under a harsh reaction condition appears as the main obstacle toward its commercialization. In the present work, a facile hydrothermal synthesis procedure was adopted to prepare a robust Ru-based catalyst. Among the various combinations, a 1% Ru supported over Zr0.5Ce0.5O2 nanorod catalyst showed enhanced coke resistance and almost stable activity during 200 h activity analysis. Promotion of Ru/Zr0.5Ce0.5O2 with an optimum amount of Gd2O3 improved catalyst stability, which was attributed to the strong interaction of Ru with Gd2O3 leading to smaller Ru particle size (∼5 nm) and an improved OSC was inhibiting coke deposition. Promotion with 0.5% Gd2O3 further lowered the apparent activation energy of methane conversion to ∼20.6 kcal/mol without changing the reaction orders significantly. DFT calculation confirmed, due to the orbital similarity, methane cracking is preferred over Ru atoms and CO2 activation occurred on Gd atoms. ©
view abstract doi: 10.1021/acsanm.0c03140 2021 • 385 Implementation of formation mechanisms in DEM simulation of the spheronization process of pharmaceutical pellets
Weis, D. and Grohn, P. and Evers, M. and Thommes, M. and García, E. and Antonyuk, S.
Powder Technology 378 667-679 (2021)In the production process of pharmaceutical pellets with a narrow size distribution and a high sphericity, a combined extrusion-spheronization technique is frequently used. The rounding of the wet cylindrical extrudates in the spheronizer after the extrusion step is influenced by various interfering mechanisms, in particular plastic deformation, breakage, attrition and coalescence. Due to the complexity of these mechanisms which depend on the particle dynamics, there is no sufficient description of the particle rounding process in the spheronizer. In this study, the Discrete Element Method (DEM) which runs on the micro scale is coupled with a Particle Shape Evolution (PSE) model on the macro scale to describe how the particle shape changes due to collisions. For the DEM simulation a new contact model was used which was developed to capture the cyclic, dominant visco plastic deformation behaviour. Based on the DEM collision data, the changing particle shape was described in the PSE model by applying the proposed submodels for the different formation mechanisms. The resulting particle shapes obtained with this simulation framework are in a good agreement with experimental data. © 2020
view abstract doi: 10.1016/j.powtec.2020.09.013 2021 • 384 Improved Maxwell Model Approach and its Applicability toward Lifetime Prediction of Biobased Viscoelastic Fibers
Schippers, C. and Tsarkova, L.A. and Bahners, T. and Gutmann, J.S. and Cleve, E.
Macromolecular Materials and Engineering 306 (2021)The evaluation of relaxation measurements is a well-established technique for predicting the lifetime of polymer materials, with research primarily focusing on increasing prediction accuracy and minimizing material testing time. The current study presents a novel approach toward describing the long-term behavior of viscoelastic polymers based on the Maxwell model. It assumes a mean relaxation time of the polymer chains in conjunction with a dimensionless number that accounts for averaged polymer chain inhomogeneities. This coefficient is analogous to the dimensionless number, which successfully describes the asymmetry of both the Weibull distribution and of particle size distribution according to the Rosin, Rammler, Sperling and Bennet model. In comparison to earlier models based on time-superposition principles, the current approach enables lifetime prediction using a single short-term measurement, which must be taken at a properly chosen applied strain. The applicability of the new model in predicting the long-term behavior has been demonstrated by the analysis of the relaxation behavior of semi-crystalline bio-based fibers. © 2021 The Authors. Macromolecular Materials and Engineering published by Wiley-VCH GmbH
view abstract doi: 10.1002/mame.202100443 2021 • 383 Influence of powder characteristics on the structural and the mechanical properties of additively manufactured Zr-based bulk metallic glass
Wegner, J. and Frey, M. and Piechotta, M. and Neuber, N. and Adam, B. and Platt, S. and Ruschel, L. and Schnell, N. and Riegler, S.S. and Jiang, H.-R. and Witt, G. and Busch, R. and Kleszczynski, S.
Materials and Design 209 (2021)Additive manufacturing of Zr-based bulk metallic glasses (BMGs) is subject to growing scientific and industrial attention. Laser-based powder bed fusion of metals (PBF-LB/M) becomes a key technology to overcome current restrictions of size and geometry in the manufacturing of BMGs. For industrial application, further knowledge about defect formation, such as porosity and crystallization, is mandatory to develop processing strategies and suitable quality assurance. In this context, the influence of the particle size distribution, oxygen contamination, and applied process parameters during the PBF-LB/M of the glass-forming alloy AMZ4 (in at.% Zr59.3Cu28.8Al10.4Nb1.5) on the structural and mechanical properties were evaluated. It was found that the addition of SiO2 flow aid to the feedstock is suitable to increase flowability without impeding fabrication of the amorphous material. Furthermore, the processing of partially crystalline powder particles into amorphous samples is demonstrated. It indicates that today's high effort producing amorphous powders and thus the production costs can be reduced. Flexural bending tests and high-energy synchrotron X-ray diffraction reveal that the powder feedstock's oxygen content is crucial for the amorphization, embrittlement, and flexural strength of PBF-LB/M processed Zr-based BMGs. © 2021
view abstract doi: 10.1016/j.matdes.2021.109976 2021 • 382 Influence of the Brazing Paste Composition on the Wetting Behavior of Reactive Air Brazed Metal–Ceramic Joints
Waetzig, K. and Schilm, J. and Mosch, S. and Tillmann, W. and Eilers, A. and Wojarski, L.
Advanced Engineering Materials 23 (2021)Reactive air brazing (RAB) is a cost-effective way to produce ceramic–ceramic or ceramic–metal brazed joints in air, without applying a protective gas atmosphere or a vacuum. In addition to conventional furnace technology, the brazing with induction heating can also be used effectively. Within the scope of this study the shrinkage and wetting behavior of self-developed brazing pastes with different CuO contents and two qualities of silver powders with coarse and fine particle size are investigated by optical dilatometry on alumina (Al2O3, 99.7% purity). Thereby, the fine silver powder quality reveals a significant swelling effect at high temperatures, leading to an expansion of densified powder compacts caused by evolving gases. Joining tests are performed on ceramic–steel brazed joints using a muffle furnace and induction heating for short brazing cycles. The brazing seams and interfaces of the joints are investigated using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). As a result, correlations between the brazing filler metal composition, the steel, and the brazing conditions are obtained. © 2020 The Authors. Published by Wiley-VCH GmbH
view abstract doi: 10.1002/adem.202000711 2021 • 381 Influence of the particle size on selective 2-propanol gas-phase oxidation over Co3O4 nanospheres
Falk, T. and Anke, S. and Hajiyani, H. and Saddeler, S. and Schulz, S. and Pentcheva, R. and Peng, B. and Muhler, M.
Catalysis Science and Technology 11 7552-7562 (2021)Co3O4 nanospheres with a mean diameter of 19 nm were applied in the selective oxidation of 2-propanol to acetone in the gas phase. Compared with 9 nm spheres, the 19 nm spheres exhibited superior catalytic activity and stability with 100% selectivity to acetone up to 500 K. Transmission electron microscopy, N2 physisorption, 2-propanol and O2 temperature-programmed desorption, and 2-propanol temperature-programmed surface reaction in O2 were applied to characterize the bulk and surface properties. Despite the smaller specific surface area (35 m2 g-1), an increased 2-propanol adsorption capacity was observed for the larger nanospheres ascribed to a preferential (110) surface orientation. Temperature-programmed oxidation experiments after reaction showed multilayer coke deposition and severe reduction of the Co3O4 surface, but excellent stability was maintained at 430 K using the 19 nm spheres in a steady-state oxidation experiment for 100 h with only 10% loss of the initial activity. The good agreement of the 2-propanol decomposition profiles indicates that the superior activity is caused by the enhanced interaction of the larger nanospheres with O2. A Mars-van Krevelen mechanism on the (110) surface was identified by density functional theory calculations with a Hubbard U term, favoring faster reoxidation compared with the (100) surface predominantly exposed by the 9 nm spheres. © The Royal Society of Chemistry.
view abstract doi: 10.1039/d1cy00944c 2021 • 380 Investigation on flow dynamics and temperatures of solid fuel particles in a gas-assisted oxy-fuel combustion chamber
Schneider, H. and Valentiner, S. and Vorobiev, N. and Böhm, B. and Schiemann, M. and Scherer, V. and Kneer, R. and Dreizler, A.
Fuel 286 (2021)Flow dynamics and temperatures of solid fuel particles strongly influence flame stabilization, local heat release and fuel conversion inside pulverized solid fuel combustors. To investigate these phenomena, experiments are carried out under well-controlled inflow and boundary conditions inside a gas-assisted, swirled oxy-fuel combustion chamber. Flow fields of small particles that represent the gas phase velocity are determined in the near-burner region by PIV using a particle separation algorithm. Trajectories of large solid fuel particles are evaluated in a two-dimensional plane using a combined high-speed PIV/PTV approach. Particle temperatures and particles sizes are measured at different levels downstream the burner exit to reveal different stages of combustion. Therefore, a two-color pyrometer is used that dissolve single particles to achieve local particle temperature and particle size distributions. Two oxy-fuel operation conditions with an oxygen fraction of 33%V and a reference operation point in air are investigated within this study. In the flow fields of the gas phase the impact of the atmosphere is clearly visible in the spatial expansion of the internal recirculation area. Regions of high slip velocities and high heat release could be identified by analyzing particle trajectories in terms of direction, velocity and acceleration. Residence times of small and large particles are estimated from the flow fields. Significantly larger residence times are observed for large particles which leads to higher burn out rates in the near-burner region. Furthermore, particle temperature measurements reveal similar particle temperatures for the investigated oxy-fuel and air operation conditions. © 2020 Elsevier Ltd
view abstract doi: 10.1016/j.fuel.2020.119424 2021 • 379 Mechanical milling to foster the solid solution formation and densification in Cr-W-Si for hot-pressing of PVD target materials
Tillmann, W. and Fehr, A. and Heringhaus, M.
Advanced Powder Technology 32 1927-1934 (2021)Based on the significantly different melting points and high oxygen affinities, the fabrication of chromium-based tungsten silicides is restricted to powder metallurgical production routes. To foster particle contacts and diffusion processes between chromium and tungsten, which are known to necessitate long sintering times, mechanical alloying or milling processes prior to sintering are established. Nonetheless, due to spinodal decomposition of Cr and W, the solid solution formation is complex and yet little understood. For this reason, the influence of the mechanical milling time (0–24 h) on the crystal structure and the microstructural properties of hot-pressed 60Cr30W10Si (wt.–%) is examined. In this context, two different powders containing a different tungsten particle size (0.8 and 3 µm) were mechanically alloyed to analyze the impact on the phase formation and the particle distribution in the microstructure. It was shown that mechanical milling supported the mechanical clamping between the particles. However, the increased milling times significantly decreased the crystallite sizes of the particles and fostered the tungsten solubility in the Cr-rich (Cr, W) solid solution formed during sintering, thus supporting the densification. © 2021 The Society of Powder Technology Japan
view abstract doi: 10.1016/j.apt.2021.04.001 2021 • 378 Metal-Ligand Interface and Internal Structure of Ultrasmall Silver Nanoparticles (2 nm)
Wetzel, O. and Hosseini, S. and Loza, K. and Heggen, M. and Prymak, O. and Bayer, P. and Beuck, C. and Schaller, T. and Niemeyer, F. and Weidenthaler, C. and Epple, M.
Journal of Physical Chemistry B 125 5645-5659 (2021)Ultrasmall silver nanoparticles were prepared by reduction with NaBH4 and surface-terminated with glutathione (GSH). The particles had a solid core diameter of 2 nm as shown by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). NMR-DOSY gave a hydrodynamic diameter of 2 to 2.8 nm. X-ray photoelectron spectroscopy (XPS) showed that silver is bound to the thiol group of the central cysteine in glutathione under partial oxidation to silver(+I). In turn, the thiol group is deprotonated to thiolate. X-ray powder diffraction (XRD) together with Rietveld refinement confirmed a twinned (polycrystalline) fcc structure of ultrasmall silver nanoparticles with a lattice compression of about 0.9% compared to bulk silver metal. By NMR spectroscopy, the interaction between the glutathione ligand and the silver surface was analyzed, also with 13C-labeled glutathione. The adsorbed glutathione is fully intact and binds to the silver surface via cysteine. In situ 1H NMR spectroscopy up to 85 °C in dispersion showed that the glutathione ligand did not detach from the surface of the silver nanoparticle, i.e. the silver-sulfur bond is remarkably strong. The ultrasmall nanoparticles had a higher cytotoxicity than bigger particles in in vitro cell culture with HeLa cells with a cytotoxic concentration of about 1 μg mL-1 after 24 h incubation. The overall stoichiometry of the nanoparticles was about Ag∼250GSH∼155. © 2021 The Authors. Published by American Chemical Society.
view abstract doi: 10.1021/acs.jpcb.1c02512 2021 • 377 Near-threshold soot formation in premixed flames at elevated pressure
Mi, X. and Saylam, A. and Endres, T. and Schulz, C. and Dreier, T.
Carbon 181 143-154 (2021)Soot formation at lean-threshold conditions referred to as “near-threshold sooting conditions” (i.e., with stoichiometry, φ, around 1.90 for ethene as a fuel) are studied in laminar premixed ethylene/air flames at pressure from 1 to 10 bar. Laser extinction is used to measure the soot volume fraction. Time-resolved laser-induced incandescence (TiRe-LII) is used to determine particle diameters from the LII signal temporal decay after pulsed laser heating. Thermophoretic sampling is applied to extract particle samples from the flame and ex situ transmission electron microscopy (TEM) is used to measure particle sizes and morphology. The soot volume fraction scales with pressure in a power-law function with the parameter n as 1.4 to 1.9 for flames at the equivalence ratio (φ = 2.1) even at the onset of soot formation. The elevated dependence of soot volume fraction on height above burner is detected with increasing pressure in the near-threshold sooting conditions. The measured soot diameter increases with pressure and equivalence ratio and its sensitivity to the equivalence ratio increases with increasing pressure. The TiRe-LII signal decay varies only little with height above burner and laser fluence in the near-threshold sooting flame (φ = 1.90–1.95), which indicates that the soot particle surface growth and oxidation are balanced. For a slightly sooting flame, TEM measurements from thermophoretically-sampled soot agree well with the LIIsim-evaluated particle size, indicating the reliability of TiRe-LII particle diameter determination under near-threshold conditions. © 2021 Elsevier Ltd
view abstract doi: 10.1016/j.carbon.2021.05.014 2021 • 376 Photoluminescence of Fully Inorganic Colloidal Gold Nanocluster and Their Manipulation Using Surface Charge Effects
Ziefuss, A.R. and Steenbock, T. and Benner, D. and Plech, A. and Göttlicher, J. and Teubner, M. and Grimm-Lebsanft, B. and Rehbock, C. and Comby-Zerbino, C. and Antoine, R. and Amans, D. and Chakraborty, I. and Bester, G. and Nac...
Advanced Materials (2021)Fully inorganic, colloidal gold nanoclusters (NCs) constitute a new class of nanomaterials that are clearly distinguishable from their commonly studied metal–organic ligand-capped counterparts. As their synthesis by chemical methods is challenging, details about their optical properties remain widely unknown. In this work, laser fragmentation in liquids is performed to produce fully inorganic and size-controlled colloidal gold NCs with monomodal particle size distributions and an fcc-like structure. Results reveal that these NCs exhibit highly pronounced photoluminescence with quantum yields of 2%. The emission behavior of small (2–2.5 nm) and ultrasmall (<1 nm) NCs is significantly different and dominated by either core- or surface-based emission states. It is further verified that emission intensities are a function of the surface charge density, which is easily controllable by the pH of the surrounding medium. This experimentally observed correlation between surface charge and photoluminescence emission intensity is confirmed by density functional theoretical simulations, demonstrating that fully inorganic NCs provide an appropriate material to bridge the gap between experimental and computational studies of NCs. The presented study deepens the understanding of electronic structures in fully inorganic colloidal gold NCs and how to systematically tune their optical properties via surface charge density and particle size. © 2021 The Authors. Advanced Materials published by Wiley-VCH GmbH
view abstract doi: 10.1002/adma.202101549 2021 • 375 Site-specific facet protection of gold nanoparticles inside a 3D DNA origami box: a tool for molecular plasmonics
Erkelenz, M. and Kosinski, R. and Sritharan, O. and Giesler, H. and Saccà, B. and Schlücker, S.
Chemical Communications 57 3151-3153 (2021)Bare gold nanocubes and nanospheres with different sizes are incorporated into a rationally designed 3D DNA origami box. The encaged particles expose a gold surface accessible for subsequent site-specific functionalization, for example, for applications in molecular plasmonics such as SERS or SEF. © The Royal Society of Chemistry 2021.
view abstract doi: 10.1039/d0cc07712g 2021 • 374 Spatially resolved GHz magnetization dynamics of a magnetite nano-particle chain inside a magnetotactic bacterium
Feggeler, T. and Meckenstock, R. and Spoddig, D. and Zingsem, B.W. and Ohldag, H. and Wende, H. and Farle, M. and Winklhofer, M. and Ollefs, K.J.
Physical Review Research 3 (2021)Understanding magnonic properties of nonperiodic magnetic nanostructures requires real-space imaging of ferromagnetic resonance modes with spatial resolution well below the optical diffraction limit and sampling rates in the 5-100 GHz range. Here, we demonstrate element-specific scanning transmission x-ray microscopy-detected ferromagnetic resonance (STXM-FMR) applied to a chain of dipolarly coupled nano-particles (40-50 nm particle size) inside a single cell of a magnetotactic bacterium Magnetospirillum magnetotacticum. The ferromagnetic resonance mode of the nano-particle chain driven at 6.748 GHz and probed with 50 nm x-ray focus size was found to have a uniform phase response but non-uniform amplitude response along the chain segments due to the superposition of dipolar coupled modes of chain segments and individual particles, in agreement with micromagnetic simulations. © 2021 Published by the American Physical Society
view abstract doi: 10.1103/PhysRevResearch.3.033036 2021 • 373 Spray-Flame Synthesis of LaMnO3+δNanoparticles for Selective CO Oxidation (SELOX)
Angel, S. and Tapia, J.D. and Gallego, J. and Hagemann, U. and Wiggers, H.
Energy and Fuels (2021)LaMnO3+δ nanoperovskites were prepared via the continuous and scalable spray-flame synthesis (SFS) technique from metal nitrate-based solutions by using either ethanol (EtOH) as solvent or a mixture of ethanol (50 vol %) and 2-ethylhexanoic acid (50 vol %) (EtOH/2-EHA). Solutions based on pure EtOH generated a mixture of several phases and a broad and multimodal particle size distribution, which is attributed to a combination of gas-to-particle and droplet-to particle formation of particles. The product contained a bimodal distribution of the orthorhombic (Pnma II) LaMnO3 perovskite-like phase and additional, unwanted phases such as La2O3 and sub-20 nm Mn-rich amorphous/poorly crystalline particles. The incorporation of 2-EHA led to high surface area (>100 m2 g-1), small, and crystalline LaMnO3+δ nanoparticles with sizes ranging between 4 and 15 nm in the presence of few sub-200 nm particles (<10 wt %). This sample is mainly composed of the orthorhombic Mn4+ rich (Pnma I) LaMnO3+δ phase, and it counts with a very high specific surface area that makes it highly promising for catalytic applications. FTIR and UV-VIS spectroscopy of the precursor solutions revealed the oxidation of the Mn2+ precursor in advance of the particle formation process along with the esterification of the solvent mixture. It is assumed that the observed liquid-phase oxidation supports the formation of Mn4+-rich perovskites. According to O2-TPD and H2-TPR measurements, the EtOH/2-EHA sample presented a much higher formation of adsorbed active oxygen species and higher reducibility than the EtOH-made material, leading to a superior performance for both the catalytic oxidation of CO and the selective oxidation (SELOX) of CO. © 2021 American Chemical Society.
view abstract doi: 10.1021/acs.energyfuels.0c03659 2021 • 372 Spray-flame synthesis of LaMO3(M = Mn, Fe, Co) perovskite nanomaterials: Effect of spray droplet size and esterification on particle size distribution
Angel, S. and Schneider, F. and Apazeller, S. and Kaziur-Cegla, W. and Schmidt, T.C. and Schulz, C. and Wiggers, H.
Proceedings of the Combustion Institute 38 1279-1287 (2021)Perovskite nanomaterials such as LaMnO3, LaFeO3, and LaCoO3were synthesized in a spray flame from metal nitrates dissolved in combustible liquids. The addition of low-boiling solvents such as 2-ethylhexanoic acid (2-EHA) to the ethanol-based solutions supports the formation of phase-pure particles with unimodal particle-size distribution in the 10-nm range attributed to enhanced evaporation through micro-explosions. Nevertheless, in many cases, a second particle mode with sizes of a few hundred nanometers is formed. In this paper, we investigate two possible reasons for the appearance of large particles. Firstly, we analyze the effect of the oxygen dispersion gas flow applied in the two-fluid nozzle on the droplet size distributions of burning sprays using phase Doppler anemometry. We identified that an increase of the dispersion gas flow significantly decreases the number concentration of large droplets (>30 μm), which causes a significant increase of the BET surface area of as-synthesized LaMnO3and LaCoO3with increasing dispersion gas flow from 60 m2/g (5 slm dispersion gas) to 100 m2/g (8 slm). Secondly, the esterification in the mixture of solvents towards ethyl-2-ethylhexanoate, which is associated with the release of water as a byproduct, was analyzed by GC/MS. The ester concentration in the iron-containing solution was found to be up to nine times higher than in cobalt or manganese precursor solutions. Simultaneously, the produced LaFeO3materials show lower BET surface areas and the increasing dispersion gas flow has a minor effect on this material than on the cobalt and manganese perovskite cases. We attribute this to the fact that water formed during esterification forces the hydrolysis of iron nitrate and the formation of large particles within the droplets. © 2021 Elsevier Ltd. All rights reserved.
view abstract doi: 10.1016/j.proci.2020.07.116 2021 • 371 Synthesis, sintering, and effect of surface roughness on oxidation of submicron Ti2AlC ceramics
Badie, S. and Dash, A. and Sohn, Y.J. and Vaßen, R. and Guillon, O. and Gonzalez-Julian, J.
Journal of the American Ceramic Society 104 1669-1688 (2021)Submicron Ti2AlC MAX phase powder was synthesized by molten salt shielded synthesis (MS3) using a Ti:Al:C molar ratio of 2:1:0.9 at a process temperature of 1000°C for 5 hours. The synthesized powder presented a mean particle size of ~0.9 µm and a purity of 91 wt. % Ti2AlC, containing 6 wt. % Ti3AlC2. The Ti2AlC powder was sintered by pressureless sintering, achieving a maximal relative density of 90%, hence field-assisted sintering technology/spark plasma sintering was used to enhance densification. The fine-grained microstructure was preserved, and phase purity of Ti2AlC was unaltered in the latter case, with a relative density of 98.5%. Oxidation was performed at 1200°C for 50 hours in static air of dense monolithic Ti2AlC with different surface finish, (polished, ground and sandblasted) which resulted in the formation of an approx. 8 µm thin aluminum oxide (Al2O3) layer decorated with titanium dioxide (rutile, TiO2) colonies. Surface quality had no influence on Al2O3 scale thickness, but the amount and size of TiO2 crystals increased with surface roughness. A phenomenon of rumpling of the thermally grown oxide (TGO) was observed and a model to estimate the extent of deformation is proposed. © 2020 The Authors. Journal of the American Ceramic Society published by Wiley Periodicals LLC on behalf of American
view abstract doi: 10.1111/jace.17582 2020 • 370 A model flow reactor design for the study of nanoparticle structure formation under well-defined conditions
Rosenberger, T. and Sellmann, J. and Wlokas, I. and Kruis, F.E.
Review of Scientific Instruments 91 (2020)Structure formation models describe the change of the particle structure, e.g., by sintering or coating, as a function of the residence time and temperature. For the validation of these models, precise experimental data are required. The precise determination of the required data is difficult due to simultaneously acting mechanisms leading to particle structure formation as well as their dependency on various particle properties and process conditions in the reactor. In this work, a model flow reactor (MFR) is designed and optimized, supported by a validated computational fluid dynamic simulation, to determine the structure formation of nanoparticles under well-defined conditions. Online instrumentation is used to measure the particle mass and different equivalent diameter to detect changes of the particle shape and to calculate the particle structure, defined by the primary particle size, the number of primary particles per agglomerate, coating thickness, effective density, and fractal dimension, by means of structural models. High precision is achieved by examining size-selected particles in a low number concentration and a laminar flow field. Coagulation can be neglected due to the low particle number concentration. Structure formation is restricted to a defined region by direct particle trajectories from the water-cooled aerosol inlet to the water-cooled outlet. A preheated sheath gas is used to concentrate the aerosol on the centerline. The simulated particle trajectories exhibit a well-defined and narrow temperature residence time distribution. Residence times of at least 1 s in the temperature range from 500 K to 1400 K are achieved. The operation of the MFR is demonstrated by the sintering of size-selected FexOy agglomerates with measurements of the particle size and mass distribution as a function of the temperature. An increase of the effective density, resulting from the decreasing particle size at constant particle mass, is observed. © 2020 Author(s).
view abstract doi: 10.1063/5.0018880 2020 • 369 A Novel Branched Copolymer-Containing Anticancer Drug for Targeted Therapy: In Vitro Research
Yurchenko, A. and Nikitina, N. and Sokolova, V. and Prylutska, S. and Kuziv, Y. and Virych, P. and Chumachenko, V. and Kutsevol, N. and Ponomarenko, S. and Prylutskyy, Y. and Epple, M.
BioNanoScience 10 249-259 (2020)The viability of cancer cell lines (human transformed cervix epithelial cells, HeLa, and osteoblastic cell line from a C57BL/6 mouse calvaria, MC3T3, as models for cancer cells) was studied using MTT and live/dead assays after incubation with a branched copolymer dextran-graft polyacrylamide in anionic form (D-g-PAAan) as nanocarrier for drugs, doxorubicin (Dox), cisplatin (Cis), as well as their D-g-PAAan+Dox and D-g-PAAan+Cis mixtures, as a function of the concentration. Fourier transform infrared spectroscopy clearly indicates the complex formation of Cis and Dox with the D-g-PAAan branched copolymer. The size distribution of particles in aqueous solution and its stability were determined by dynamic light scattering. The in vitro uptake of studied particles into cancer cells was demonstrated by confocal laser scanning microscopy. It was found that D-g-PAAan+Dox particles in contrast to Dox alone showed higher toxicity towards cancer cells. This indicates the possibility of further preclinical studies of the water-soluble D-g-PAAan+Dox particles on animal tumor models in vivo as a promising anticancer agent. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.
view abstract doi: 10.1007/s12668-019-00700-5 2020 • 368 Aerosol synthesis of titanium nitride nanoparticles by direct current arc discharge method
Fu, Q. and Kokalj, D. and Stangier, D. and Kruis, F.E. and Tillmann, W.
Advanced Powder Technology 31 4119-4128 (2020)Arc discharge synthesis has industrial relevance due to its low cost and scale-up potential. The production of titanium nitride nanoparticles was achieved by direct current arc discharge in an atmospheric-pressured ambient composed of N2 and Ar. We systematically investigated the effect of the synthesis parameters, including quench gas velocity, quench gas composition, and applied arc current, on the particle quality, yield, and size. It is found that increasing quench gas velocity enables to produce particles with a primary size of 10–15 nm, while titanium nitride particles of 20–50 nm are produced at low quench gas velocity based on scanning electron microscope (SEM) analysis. X-ray diffraction (XRD) results indicated that titanium nitride particles produced at various nitrogen compositions are almost stoichiometric, while the crystallite size increases almost 20 nm when increasing nitrogen contents in the quench gas. Quench gas composition also has a significant impact on the arc voltage as well as particle production rate. When increasing the nitrogen concentration from 20% to 100%, the production rate can be enhanced by a factor of three. Besides, raising the applied arc current from 12 A to 50 A leads to a yield enhancement of factor 10. According to the Brunauer-Emmett-Teller (BET) measurement, the increase of applied arc current has a limited impact on primary particle size. The enhancement in particle production rate is mainly reflected by the larger agglomerate sizes and agglomerate number concentration. Additionally, based on experimental observations and previous studies, a mechanism is presented to explain the growth of deposits on the cathode tip. © 2020 The Society of Powder Technology Japan
view abstract doi: 10.1016/j.apt.2020.08.012 2020 • 367 Continuous-Flow Flat Jet Setup for Uniform Pulsed Laser Postprocessing of Colloids
Zerebecki, S. and Reichenberger, S. and Barcikowski, S.
Journal of Physical Chemistry A 124 11125-11132 (2020)Pulsed laser postprocessing (PLPP) of colloidal nanoparticles and related laser fragmentation in liquid (LFL) using a liquid jet setup have become an acknowledged tool to reduce the nanoparticle diameter down to a few nanometers, alter the crystal phase, or increase the defect density under high-purity and continuous-flow conditions. In recent studies on LFL that were conducted with a cylindrical liquid jet, intensity gradients and related incomplete illumination of the volume element passing through the laser beam path were reported to cause a broadening of the product particle size distribution, melting, and phase segregation. In this paper, we present a new flat jet design, which reduces the deviation of the laser intensity up to 10 times compared to the conventional cylindrical liquid jet. The experimental threshold intensity for gold nanoparticle fragmentation found with the cylindrical setup strongly deviates from the theoretical prediction, while they are in very good agreement for the flat jet setup. Additionally, a narrow product size fraction of 3 ± 2 nm was found for the flat jet, while the main product fraction gained from the cylindrical jet was 10 ± 8 nm in size under the same conditions. Consequently, the flat jet setup allows us not only to study laser fragmentation mechanisms with higher precision but also to gain product particles with narrow particle size distribution at single pulse per particle conditions even at elevated mass concentrations (>50 mg L-1). In future studies, these promising results also render the flat jet setup relevant for the other disciplines of PLPP such as laser melting and defect engineering. © 2020 American Chemical Society.
view abstract doi: 10.1021/acs.jpca.0c08787 2020 • 366 Development of a recycling strategy for grinding sludge using supersolidus liquid phase sintering
Hankel, J. and Jäger, S. and Weber, S.
Journal of Cleaner Production 263 (2020)Recycling strategies for waste products from grinding processes have become an essential concern for the industrial sector, as up to 250,000 tons of grinding sludge is generated annually in Germany alone. In this paper, a suitable recycling strategy for the recovery of the metallic component of industrial sludge generated from cold work tool steel grinding is investigated and reported. Possible reuse of the recovered metallic material as a precursor for supersolidus liquid phase sintering (SLPS), a powder metallurgy process, is assessed for the first time. Using a novel technique, including washing, dry screening and magnetic separation, 50 wt% metallic swarf and 50 wt% abrasives can be recovered from dried, industrial grinding sludge. These metallic swarf are a mixture of discontinuous and continuous microchips with a particle size of up to 250 μm. The metallic swarf tend to agglomerate, resulting in larger accumulations and a correspondingly larger overall size with a particle size of over 1000 μm. Using SLPS, the densification of the metallic swarf was considered promising, as density increases with increasing sintering temperature. A maximum density of 76 vol% was achieved, owing to the morphology of the swarf. Occasionally, a few abrasives were observed in the microstructure. Hence, a new sustainable recycling strategy for the recovery of the metallic swarf in industrial grinding sludge has been proposed and the reuse of swarf as precursor for SLPS has demonstrated promising results. Further work is being undertaken to improve the densification of the metallic swarf by SLPS. © 2020 Elsevier Ltd
view abstract doi: 10.1016/j.jclepro.2020.121501 2020 • 365 Effect of O2/CO2 atmospheres on coal fragmentation
Bareschino, P. and Urciuolo, M. and Scherer, V. and Chirone, R. and Senneca, O.
Fuel 267 (2020)Recently, a single particle pyrolysis-combustion fragmentation model has been developed (Senneca et al., 2013, 2017) [1,2] to predict the propensity of coal particles to fragment under a wide range of heating conditions as a consequence of mechanical failure of the particle. Stress inside the particle arises from thermal shock, associated to particles’ heat up, as well as from overpressure generated by volatiles release upon devolatilization. The model is now used to calculate the propensity of coal particles to undergo fragmentation in the early stages of oxy-combustion, with gaseous atmospheres of 5–30% O2 in CO2 in entrained flow and fluidized beds reactors. Accordingly particles size of 0.1–10 mm are assumed, temperatures of 1123 and 2073 K, heating rates of 100 and 10,000 K/s. Results show that under entrained flow reactor conditions the particles break in the first 20–30 ms, producing a bimodal particle-size distribution. Under fluidized bed conditions, the particles undergo explosive fragmentation after 1–2 s, before pyrolysis is complete, generating broad particle size distribution. In both cases fragmentation occurs over short timescales compared to char combustion and gasification. Operative conditions where fragmentation occurs before or in parallel with char combustion or gasification are inferred by comparing on an Arrhenius plot the timescale of fragmentation and heterogeneous reactions for a larger array of operating conditions. The figure reveals that for high reaction temperatures, more reactive coals, larger particles size, gasification reactions can have an important role and maybe enhance porosity and percolative fragmentation. © 2020 Elsevier Ltd
view abstract doi: 10.1016/j.fuel.2020.117145 2020 • 364 Effect of Spray Parameters in a Spray Flame Reactor During FexOy Nanoparticles Synthesis
Carvajal, L. and Buitrago-Sierra, R. and Santamaría, A. and Angel, S. and Wiggers, H. and Gallego, J.
Journal of Thermal Spray Technology 29 368-383 (2020)Abstract: Synthesis and characterization of FexOy nanoparticles were carried out in order to study reaction parameters influence in a spray flame reactor. FexOy powders were prepared with three different precursors aiming to understand how the reactor conditions, dispersion gas flow, and precursor solution flow affect morphology, shape, particle size distribution, crystalline phases, and residue content of the obtained materials. Thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy (TEM), x-ray diffraction (XRD), and Raman spectroscopy were employed to characterize the materials. In addition, magnetic behavior of the obtained samples was evaluated. It was found that the evaluated parameters influenced the residue contents obtaining weight changes from 10 to 35%. Particle size distribution centers also showed differences between 17 and 24 nm. By XRD, Raman, and TEM, the presence of hematite (a-Fe2O3), maghemite (γ-Fe2O3), and magnetite (Fe3O4) was evidenced and explained based on the gas and liquid content in the flame. Additionally, the saturation magnetization was measured for selected samples, obtaining values between 26 and 32 emu g−1. These magnetic measurements were correlated with the crystalline phase composition and particle size distributions. Graphic Abstract: [Figure not available: see fulltext.] © 2020, ASM International.
view abstract doi: 10.1007/s11666-020-00991-1 2020 • 363 Effective size separation of laser-generated, surfactant-free nanoparticles by continuous centrifugation
Kohsakowski, S. and Seiser, F. and Wiederrecht, J.-P. and Reichenberger, S. and Vinnay, T. and Barcikowski, S. and Marzun, G.
Nanotechnology 31 (2020)High-power, nanosecond, pulsed-laser ablation in liquids enables the continuous synthesis of highly pure colloidal nanoparticles (NPs) at an application-relevant scale. The gained mass-weighted particle size distribution is however often reported to be broad, requiring post treatment like centrifugation to remove undesired particle size fractions. To date, available centrifugation techniques are generally discontinuous, limiting the throughput and hindering economic upscaling. Hence, throughout this paper, a scalable, continuously operating centrifugation of laser-generated platinum NPs in a tubular bowl centrifuge is reported for the first time. To that end, using a 121 W ns-laser, the continuous production of a colloidal suspension of NPs, yet with broad particle size distribution has been employed, yielding productivities of 1-2 g h-1 for gold, silver, and platinum. The power-specific productivities (Au: 18 mg h-1 W-1, Pt: 13 mg h-1 W-1, Ag: 8 mg h-1 W-1, Ni: 6 mg h-1 W-1) are far higher than reported before. Subsequent downstream integration of a continuously operating tubular bowl centrifuge was successfully achieved for Pt NPs allowing the removal of undesired particle size with high throughput. By means of a systematic study of relevant centrifugation parameters involved, effective size optimization and respective size sharpness parameters for a maximum Pt NP diameter of 10 nm are reported. The results of the experimental centrifugation of laser-generated Pt NPs were in excellent agreement with the theoretically calculated cut-off diameter. After centrifugation with optimized parameters (residence time of 5 min; g-force of 38,454 g), the polydispersity indices of the Pt NPs size distributions were reduced by a factor of six, and high monodispersity was observed. © 2019 IOP Publishing Ltd.
view abstract doi: 10.1088/1361-6528/ab55bd 2020 • 362 Ejector-based nanoparticle sampling from pressures down to 20 mbar
Rosenberger, T. and Neises, J. and Kiesler, D. and Kruis, F.E.
Journal of Aerosol Science 144 (2020)The application of standard online instrumentation, such as scanning mobility particle sizer (SMPS), centrifugal particle mass analyzer or aerosol particle mass analyzer (CPMA/APM), and electrical low-pressure impactor (ELPI+) to low-pressure processes is only possible with extensive modification of the devices and extensive calibrations. A low-pressure ejector is a suitable device to transfer aerosol nanoparticles from low-pressure regions to atmospheric pressure and allows the direct use of standard online instrumentation. In this work, a commercial low-pressure ejector is investigated in the pressure range from 20–180 mbar with fully-sintered and size-selected nanoparticles (15–80 nm) in order to extend the application range of online instruments to low-pressure processes and open up a new variety of analysis methods. Results are compared to our previous work which was limited to pressures above 120 mbar. A change in particle size during the measurements for fully-sintered silver particles was not observed. A particle dilution factor between 60–6500 was found. High particle losses in the ejector for large particle sizes are compensated by a lower gas dilution factor. © 2020 Elsevier Ltd
view abstract doi: 10.1016/j.jaerosci.2020.105531 2020 • 361 Evaluation of essential powder properties through complementary particle size analysis methods for laser powder bed fusion of polymers
Sommereyns, A. and Hupfeld, T. and Gökce, B. and Barcikowski, S. and Schmidt, M.
Procedia CIRP 94 116-121 (2020)The resolution of complex parts produced by laser powder bed fusion of polymers (PBF-LB/P) is defined significantly by the shape and size distribution of the feedstock powder. Its analysis is usually performed by optical measurement systems such as laser diffraction or image analysis. In this study, the most relevant particle size parameters will be extracted from a set of different measuring methods, as well as the Hausner ratio and finally discussed regarding safe and successful processability. Extracted data include the sphericity, fine fraction, volume- and number-weighted diameter distributions, and statistical significance analysis, including comparison of PA12 and carbon-black-additivated PA12. The presented results should give researchers a first impression about the suitability of polymer powders for PBF-LB/P, based on powder feedstock characterization. © 2020 The Authors. Published by Elsevier B.V.
view abstract doi: 10.1016/j.procir.2020.09.023 2020 • 360 Experimental analysis of wood pellet degradation during pneumatic conveying processes
Jägers, J. and Wirtz, S. and Scherer, V. and Behr, M.
Powder Technology 359 282-291 (2020)The size reduction of wood pellets during pneumatic transport in a laboratory test rig is investigated. For the quantification of pellet breakage and attrition, the length distribution of each bulk sample is measured in combination with the gravimetrical determination of the amount of fines before and after every conveying step. In laboratory tests a variation of pipe elements (bend radii, couplings, pipe reducer or cyclone separator), air volume and product mass flows and pellet quality is investigated. Additionally, particle velocities are determined with a stereoscopic high-speed camera set. Results demonstrate the strong dependence of wood pellet degradation on operating conditions and selection of pipe components. Increasing air volume flow and, thus, higher particle velocities induce particle size reduction, whereas increasing pellet mass flow has the opposite effect, although the influence is weak. Increasing pipe length or decreasing bend radius leads to progressive formation of fines. © 2019 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2019.10.004 2020 • 359 Experimental and numerical study on the influence of equivalence ratio on key intermediates and silica nanoparticles in flame synthesis
Karakaya, Y. and Janbazi, H. and Wlokas, I. and Levish, A. and Winterer, M. and Kasper, T.
Proceedings of the Combustion Institute (2020)Tetramethylsilane is a precursor often used for the production of flame-synthesized silica nanoparticles or coatings. This study investigates the chemical reaction mechanism of tetramethylsilane in a series of H 2 /O 2 /Ar low-pressure (p = 30 mbar) flames from fuel-lean to slightly fuel-rich flame conditions (ϕ= 0.8, 1.0 and 1.2). Mole fraction profiles are obtained by molecular-beam mass spectrometry. The experimental data are compared to simulations using a recently published reaction mechanism. The present study reveals the influence of the flame composition on the depletion of the precursor TMS, the formation of its main carbon-containing products (e.g. CO 2 and CO) and the main silicon-containing intermediates (e.g. Si(CH 3) 3 (CH 2)OO), Si(OH) 4, SiO 2, Si 4 O 10 H 4) appearing along the routes of particle formation. TEM images of synthesized particles reveal that the nanoparticles obtained from the gas-phase synthesis are spheres with a low degree of agglomeration. The particle size distribution appears to be dependent on the equivalence ratio of the synthesis flames and the changes can tentatively be traced to different particle formation pathways. The data set provided in this work can serve a basis for improvements to the reaction mechanisms of the Si/C/H/O system that are urgently needed to improve particle synthesis processes. © 2020 The Combustion Institute. Published by Elsevier Inc.
view abstract doi: 10.1016/j.proci.2020.06.096 2020 • 358 Gas atomization and laser additive manufacturing of nitrogen-alloyed martensitic stainless steel
Boes, J. and Röttger, A. and Theisen, W. and Cui, C. and Uhlenwinkel, V. and Schulz, A. and Zoch, H.-W. and Stern, F. and Tenkamp, J. and Walther, F.
Additive Manufacturing 34 (2020)Nitrogen as an alloying element can improve the corrosion resistance and the mechanical properties of stainless steels. Therefore, nitrogen-alloyed martensitic stainless steels, such as X30CrMoN151, have been developed in recent decades and conventional processing of this steel by casting or powder metallurgy is well understood. However, only very few attempts to process nitrogen-alloyed martensitically hardenable stainless steels containing more than 0.2 mass-% of carbon by laser powder bed fusion (L-PBF) have been reported so far. In this study, X30CrMoN15-1 steel powder has been produced from quasi nitrogen-free X30CrMo15-1 steel by gas atomization using N2 as the process gas to introduce nitrogen into the steel. The gas-atomized powder was characterized in terms of nitrogen content, particle size distribution, particle morphology, and flow properties. The powder was then processed by L-PBF under an N2 gas atmosphere, and microstructural investigations were performed on the L-PBF-built samples using scanning electron microscopy and X-ray computed tomography. Additionally, a first impression of the mechanical properties of the L-PBF-built steel in the as-built and quenched and tempered condition was obtained by means of fatigue tests. It was shown that a nitrogen content of 0.16 mass-% could be introduced into the steel during gas atomization. The resulting powder was successfully processed by means of L-PBF, and specimens with a high density were produced. During fatigue testing, a large amount of retained austenite in the as-built condition resulted in a greater damage tolerance of the specimens compared to the heat-treated condition. © 2020 Elsevier B.V.
view abstract doi: 10.1016/j.addma.2020.101379 2020 • 357 Genetic immunization against hepatitis B virus with calcium phosphate nanoparticles in vitro and in vivo
Rojas-Sánchez, L. and Zhang, E. and Sokolova, V. and Zhong, M. and Yan, H. and Lu, M. and Li, Q. and Yan, H. and Epple, M.
Acta Biomaterialia 110 254-265 (2020)Calcium phosphate nanoparticles were loaded with plasmid DNA and toll-like receptor ligands (TLR), i.e. CpG or flagellin, to activate antigen-presenting cells (APCs) like dendritic cells (DCs). The functionalized nanoparticles were studied in vitro on HeLa, C2C12 and BHK-21 cell lines, focusing on the expression of two specific proteins. EGFP-DNA, encoding for enhanced green fluorescent protein (EGFP), was used as a model plasmid to optimize the transfection efficiency in vitro by fluorescence microscopy and flow cytometry. Calcium phosphate nanoparticles loaded with TLR ligands and plasmid DNA encoding for the hepatitis B virus surface antigen (pHBsAg) were evaluated by in vitro and in vivo immunization experiments to identify a possible candidate for a prophylactic hepatitis B virus (HBV) vaccine. The nanoparticles induced a strong expression of HBsAg in the three cell lines. In splenocytes, the expression of the co-stimulatory molecules CD80 and CD86 was enhanced. After intramuscular injection in mice, the nanoparticles induced the expression of HBsAg, the antigen-specific T cell response, and the antigen-specific antibody response (IgG1). Statement of Significance: Hepatitis B is one of the most frequent viral infections worldwide. For preventive immunization, nanoparticles can be used which carry both an adjuvant (a stimulatory molecule) and DNA encoding for a viral antigen. After administration of such nanoparticles to cells, they are taken up by cells where the DNA is transcribed into the viral antigen (a protein). This viral antigen is inducing a virus-specific immune response. This was shown both by in vitro cell culture as well as by an extensive in vivo study in mice. © 2020 Acta Materialia Inc.
view abstract doi: 10.1016/j.actbio.2020.04.021 2020 • 356 Hard X-ray-based techniques for structural investigations of CO2methanation catalysts prepared by MOF decomposition
Prinz, N. and Schwensow, L. and Wendholt, S. and Jentys, A. and Bauer, M. and Kleist, W. and Zobel, M.
Nanoscale 12 15800-15813 (2020)Thermal decomposition of metal-organic framework (MOF) precursors is a recent method to create well-dispersed metal centers within active catalyst materials with enhanced stability, as required for dynamic operation conditions in light of challenges caused by the renewable energy supply. Here, we use a hard X-ray-based toolbox of pair distribution function (PDF) and X-ray absorption spectroscopy (XAS) analysis combined with X-ray diffraction and catalytic activity tests to investigate structure-activity correlations of methanation catalysts obtained by thermal decomposition of a Ni(BDC)(PNO) MOF precursor. Increasing the decomposition temperature from 350 to 500 °C resulted in Nifcc nanoparticles with increasing particle sizes, alongside a decrease in Ni2+ species and strain-induced peak broadening. For lower temperatures and inert atmosphere, Ni3C and NiO phases co-existed. A graphitic shell stabilized the Ni particles. Compared to an inert atmosphere, reducing conditions led to larger particles and a faster decomposition of the MOF precursor. Catalytic studies revealed that the decomposition at an intermediate temperature of 375 °C in 5% H2/He is the best set of parameters to obtain high specific surface areas while maintaining particle sizes that feature many active Ni centers for the formation of CH4. This journal is © The Royal Society of Chemistry.
view abstract doi: 10.1039/d0nr01750g 2020 • 355 Image-based size analysis of agglomerated and partially sintered particles via convolutional neural networks
Frei, M. and Kruis, F.E.
Powder Technology 360 324-336 (2020)There is a high demand for fully automated methods for the analysis of primary particle size distributions of agglomerated, sintered or occluded primary particles, due to their impact on material properties. Therefore, a novel, deep learning-based, method for the detection of such primary particles was proposed and tested, which renders a manual tuning of analysis parameters unnecessary. As a specialty, the training of the utilized convolutional neural networks was carried out using only synthetic images, thereby avoiding the laborious task of manual annotation and increasing the ground truth quality. Nevertheless, the proposed method performs excellent on real world samples of sintered silica nanoparticles with various sintering degrees and varying image conditions. In a direct comparison, the proposed method clearly outperforms two state-of-the-art methods for automated image-based particle size analysis (Hough transformation and the ImageJ ParticleSizer plug-in), thereby attaining human-like performance. © 2019 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2019.10.020 2020 • 354 Insights into the Formation, Chemical Stability, and Activity of Transient NiyP@NiO x Core-Shell Heterostructures for the Oxygen Evolution Reaction
Wilde, P. and Dieckhöfer, S. and Quast, T. and Xiang, W. and Bhatt, A. and Chen, Y.-T. and Seisel, S. and Barwe, S. and Andronescu, C. and Li, T. and Schuhmann, W. and Masa, J.
ACS Applied Energy Materials 3 2304-2309 (2020)NiyP emerged as a highly active precatalyst for the alkaline oxygen evolution reaction where structural changes play a crucial role for its catalytic performance. We probed the chemical stability of NiyP in 1 M KOH at 80 °C and examined how exposure up to 168 h affects its structure and catalytic performance. We observed selective P-leaching and formation of NiyP/NiOx core-shell heterostructures, where shell thickness increases with ageing time, which is detrimental for the activity. By tuning the particle size, we demonstrate that prevention of complete catalyst oxidation is essential to preserve the outstanding electrochemical performance of NiyP in alkaline media. © 2020 American Chemical Society.
view abstract doi: 10.1021/acsaem.9b02481 2020 • 353 On the agglomeration tendency of carbonaceous fuels in fluidized beds
Urciuolo, M. and Solimene, R. and Ammendola, P. and Krusch, S. and Scherer, V. and Salatino, P. and Chirone, R. and Senneca, O.
Fuel 277 (2020)Single particle pyrolysis and combustion experiments have been carried out in a lab scale fluidized bed reactor at temperatures of 600–850 °C. The behavior of three different fuels is compared: a bituminous coal (Auguste Victoria), a typical bitumen used in the cement industry, a carbon rich solid waste from the refinery industry, characterized by a very high content of metals. The bituminous coal and the refinery waste particles, during the pyrolysis stage, produce interesting carbon-sand aggregates. The outer shell of these aggregates is constituted by quartz sand particles embedded in a carbon matrix. The aggregates are hollow inside. The size of the cavity is comparable with that of the original coal particles, while the outer shell is larger. The increase of particle size due to aggregate formation slows down the combustion rate. For bitumen, no carbon-sand aggregates are observed. The relations between the fuel properties and aggregates formation are discussed, in particular the chemical composition and the pyrolysis kinetics are examined. It is concluded that heavy/tarry species formed in the early pyrolysis stages are most likely responsible for the capture of the sand particles and formation of aggregates. © 2020 Elsevier Ltd
view abstract doi: 10.1016/j.fuel.2020.118187 2020 • 352 On the reversible deactivation of cobalt ferrite spinel nanoparticles applied in selective 2-propanol oxidation
Anke, S. and Falk, T. and Bendt, G. and Sinev, I. and Hävecker, M. and Antoni, H. and Zegkinoglou, I. and Jeon, H. and Knop-Gericke, A. and Schlögl, R. and Roldan Cuenya, B. and Schulz, S. and Muhler, M.
Journal of Catalysis 382 57-68 (2020)CoFe2O4 nanoparticles (NPs) were synthesized by using a colloidal one-pot synthesis method based on the decomposition of metal acetylacetonates in the presence of oleyl amine. The characterization by X-ray diffraction, transmission electron microscopy and N2 physisorption revealed non-porous spinel phase CoFe2O4 NPs with an average particle size of 4 nm. The unsupported metal oxide NPs were applied in the selective oxidation of 2-propanol in a continuously operated fixed-bed reactor under quasi steady-state conditions using a heating rate of 0.5 k min−1. 2-Propanol was found to be oxidatively dehydrogenated over CoFe2O4 yielding acetone and H2O with high selectivity. Only to a minor extent dehydration to propene and total oxidation to CO2 was observed at higher temperatures. The detected low-temperature reaction pathway with maxima at 430 and 510 K was inhibited after the initial 2-propanol oxidation up to 573 K, but an oxidative treatment in O2 or N2O atmosphere led to full regeneration. No correlation between the desorbing amount or the surface oxygen species investigated by O2 temperature-programmed desorption experiments and the low-temperature activity was observed. The amounts of evolving CO2 during the TPO experiments indicate deactivation due to formation of carbonaceous species. Inhibition experiments with pre-adsorbed reaction intermediates and infrared spectroscopy identified acetate species as reversible poison, whereas carbonates are rather spectators. In addition, carbon deposition was detected by X-ray photoelectron spectroscopy, which also revealed a minor influence of cobalt reduction during the deactivation process as confirmed by X-ray absorption spectroscopy studies. © 2019 Elsevier Inc.
view abstract doi: 10.1016/j.jcat.2019.12.007 2020 • 351 One-step synthesis of carbon-supported electrocatalysts
Tigges, S. and Wöhrl, N. and Radev, I. and Hagemann, U. and Heidelmann, M. and Nguyen, T.B. and Gorelkov, S. and Schulz, S. and Lorke, A.
Beilstein Journal of Nanotechnology 11 1419-1431 (2020)Cost-efficiency, durability, and reliability of catalysts, as well as their operational lifetime, are the main challenges in chemical energy conversion. Here, we present a novel, one-step approach for the synthesis of Pt/C hybrid material by plasma-enhanced chemical vapor deposition (PE-CVD). The platinum loading, degree of oxidation, and the very narrow particle size distribution are precisely adjusted in the Pt/C hybrid material due to the simultaneous deposition of platinum and carbon during the process. The as-synthesized Pt/C hybrid materials are promising electrocatalysts for use in fuel cell applications as they show significantly improved electrochemical long-term stability compared to the industrial standard HiSPEC 4000. The PE-CVD process is furthermore expected to be extendable to the general deposition of metal-containing carbon materials from other commercially available metal acetylacetonate precursors. © 2020 Tigges et al.; licensee Beilstein-Institut.
view abstract doi: 10.3762/BJNANO.11.126 2020 • 350 Origin of Laser-Induced Colloidal Gold Surface Oxidation and Charge Density, and Its Role in Oxidation Catalysis
Ziefuß, A.R. and Haxhiaj, I. and Müller, S. and Gharib, M. and Gridina, O. and Rehbock, C. and Chakraborty, I. and Peng, B. and Muhler, M. and Parak, W.J. and Barcikowski, S. and Reichenberger, S.
Journal of Physical Chemistry C 124 20981-20990 (2020)Laser fragmentation in liquids (LFL) allows the synthesis of fully inorganic, ultrasmall gold nanoparticles, usAu NPs (<3 nm). Although the general method is well established, there is a lack of understanding the chemical processes that are triggered by the laser pulses, which may dictate the surface properties that are highly important in heterogeneous oxidation catalytic reactions. We observed the formation of radical oxygen species during LFL, which suggested that LFL is a physicochemical process that leads to particle size reductions and initiates oxidative processes. When the ionic strength in the nanoenvironment was increased, the oxidation of the first atomic layer saturated at 50%, whereby the surface charge density increases continuously. We found a correlation between the surface charge density after synthesis of colloidal nanoparticles and its behavior in catalysis. The properties of the laser-generated nanoparticles in the colloidal state appear to have predetermined the catalytic performance. We found that a smaller surface charge density of the usAu NPs was beneficial for the catalytic activity in CO and ethanol oxidation, while their peroxidase-like activity was affected less. The catalytic activity was 2 times higher for samples prepared by chloride-free LFL after ozone pretreatment compared to samples prepared in pure water. Copyright © 2020 American Chemical Society.
view abstract doi: 10.1021/acs.jpcc.0c06257 2020 • 349 Reassessing the rationale behind herbicide biosensors: The case of a photosystem II/redox polymer-based bioelectrodefs
Wang, P. and Zhao, F. and Hartmann, V. and Nowaczyk, M.M. and Ruff, A. and Schuhmann, W. and Conzuelo, F.
Bioelectrochemistry 136 (2020)Interfacing photosynthetic protein complexes with electrodes is frequently used for the identification of electron transfer mechanisms and the fabrication of biosensors. Binding of herbicide compounds to the terminal plastoquinone QB at photosystem II (PSII) causes disruption of electron flow that is associated with a diminished performance of the associated biodevice. Thus, the principle of electron transport inhibition at PSII can be used for herbicide detection and has inspired the fabrication of several biosensors for this purpose. However, the biosensor performance may reveal a more complex behavior than generally expected. As we present here for a photobioelectrode constituted by PSII embedded in a redox polymer matrix, the effect caused by inhibitors does not only impact the electron transfer from PSII but also the properties of the polymer film used for immobilization and electrical wiring of the protein complexes. Incorporation of phenolic inhibitors into the polymer film surprisingly translates into enhanced photocurrents and, in particular cases, in a higher stability of the overall electrode architecture. The achieved results stress the importance to evaluate first the possible influence of analytes of interest on the biosensor architecture as a whole and provide important insights for consideration in future design of bioelectrochemical devices. © 2020
view abstract doi: 10.1016/j.bioelechem.2020.107597 2020 • 348 Scale-dependent particle diffusivity and apparent viscosity in polymer solutions as probed by dynamic magnetic nanorheology
Hess, M. and Gratz, M. and Remmer, H. and Webers, S. and Landers, J. and Borin, D. and Ludwig, F. and Wende, H. and Odenbach, S. and Tschöpe, A. and Schmidt, A.M.
Soft Matter 16 7562-7575 (2020)In several upcoming rheological approaches, including methods of micro- and nanorheology, the measurement geometry is of critical impact on the interpretation of the results. The relative size of the probe objects employed (as compared to the intrinsic length scales of the sample to be investigated) becomes of crucial importance, and there is increasing interest to investigate the dynamic processes and mobility in nanostructured materials. A combination of different rheological approaches based on the rotation of magnetically blocked nanoprobes is used to systematically investigate the size-dependent diffusion behavior in aqueous poly(ethylene glycol) (PEG) solutions with special attention paid to the relation of probe size to characteristic length scales within the polymer solutions. We employ two types of probe particles: nickel rods of hydrodynamic length Lh between 200 nm and 650 nm, and cobalt ferrite spheres with diameter dh between 13 nm and 23 nm, and examine the influence of particle size and shape on the nanorheological information obtained in model polymer solutions based on two related, dynamic-magnetic approaches. The results confirm that as long as the investigated solutions are not entangled, and the particles are much larger than the macromolecular correlation length, a good accordance between macroscopic and nanoscopic results, whereas a strong size-dependent response is observed in cases where the particles are of similar size or smaller than the radius of gyration Rg or the correlation length ξ of the polymer solution. This journal is © The Royal Society of Chemistry.
view abstract doi: 10.1039/c9sm00747d 2020 • 347 Selective cyclohexene oxidation with O2, H2O2and: Tert -butyl hydroperoxide over spray-flame synthesized LaCo1- xFexO3nanoparticles
Büker, J. and Alkan, B. and Fu, Q. and Xia, W. and Schulwitz, J. and Waffel, D. and Falk, T. and Schulz, C. and Wiggers, H. and Muhler, M. and Peng, B.
Catalysis Science and Technology 10 5196-5206 (2020)The elimination of waste and by-product generation and reduced dependence on hazardous chemicals are the key steps towards environmentally sustainable chemical transformations. Heterogeneously catalysed oxidation of cyclohexene with environmentally friendly oxidizing agents such as O2, H2O2 and tert-butyl hydroperoxide (TBHP) has great potential to replace existing processes using stoichiometric oxidants. A series of spray-flame synthesised nanoparticulate LaCo1-xFexO3 catalysts was employed for cyclohexene oxidation, and the comparative results showed that TBHP led to the highest initial activity and allylic selectivity, but O2 resulted in higher conversion for longer reaction times. Furthermore, the influence of Fe substitution was studied, which did not show any beneficial synergistic effects. LaCoO3 was found to be the optimum catalyst for cyclohexene oxidation with O2, following first-order reaction kinetics with an apparent activation energy of 57 kJ mol-1. The catalyst showed good reusability due to its highly stable particle size, morphology and perovskite structure. 7-Oxabicyclo[4.1.0]heptan-2-one was identified to be formed by the oxidation of 2-cyclohexene-1-one with 2-cyclohexene-1-hydroperoxide. © 2020 The Royal Society of Chemistry.
view abstract doi: 10.1039/d0cy00906g 2020 • 346 Silver clusters shape determination from in-situ XANES data
Timoshenko, J. and Roese, S. and Hövel, H. and Frenkel, A.I.
Radiation Physics and Chemistry 175 (2020)Knowledge of nanoparticle size, shape and morphology and of their in-situ transformations is crucial for establishing structure-properties relationship in nanosized materials that find applications, e.g., in plasmonic devices and heterogenous catalysis. Here we demonstrate that this information can be extracted reliably from in-situ X-ray absorption near edge structure (XANES) data, by combining ab-initio XANES simulations and machine learning (artificial neural network (NN)) approaches. Here we use NN-XANES method to extract information about the size, shape and interatomic distances in silver clusters, and to monitor their changes during the temperature-controlled particle aggregation. © 2019 Elsevier Ltd
view abstract doi: 10.1016/j.radphyschem.2018.11.003 2020 • 345 Spray-flame synthesis of La(Fe, Co)O3 nano-perovskites from metal nitrates
Angel, S. and Neises, J. and Dreyer, M. and Friedel Ortega, K. and Behrens, M. and Wang, Y. and Arandiyan, H. and Schulz, C. and Wiggers, H.
AIChE Journal 66 (2020)Nano-sized perovskites were synthesized in a spray flame from nitrate precursors dissolved in ethanol and in ethanol/2-ethylhexanoic acid (2-EHA) mixtures. Experiments with ethanol led to a broad particle-size distribution and to the formation of undesired phases such as La2CoO4, La2O3, and Co3O4. The addition of 2-EHA can initiate micro explosions of the burning droplets and has been systematically investigated toward the formation of single-phase, high-surface-area LaCoO3 and LaFeO3 with a narrow size distribution. To investigate the effect of 2-EHA, temperature-dependent changes of the chemical composition of the precursor solutions were analyzed with ATR-FTIR between 23 and 70°C. In all cases, the formation of esters was identified while in the solutions containing iron, additional formation of carboxylates was observed. The synthesized materials were characterized by BET SSA, XRD, SAED and EDX-TEM and their catalytic activity was analyzed, reaching 50% CO conversion at temperatures below 160 and 300°C for LaCoO3 and LaFeO3, respectively. © 2019 The Authors. AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers.
view abstract doi: 10.1002/aic.16748 2020 • 344 Spray-flame synthesis of LaMO3 (M = Mn, Fe, Co) perovskite nanomaterials: Effect of spray droplet size and esterification on particle size distribution
Angel, S. and Schneider, F. and Apazeller, S. and Kaziur-Cegla, W. and Schmidt, T.C. and Schulz, C. and Wiggers, H.
Proceedings of the Combustion Institute (2020)Perovskite nanomaterials such as LaMnO3, LaFeO3, and LaCoO3 were synthesized in a spray flame from metal nitrates dissolved in combustible liquids. The addition of low-boiling solvents such as 2-ethylhexanoic acid (2-EHA) to the ethanol-based solutions supports the formation of phase-pure particles with unimodal particle-size distribution in the 10-nm range attributed to enhanced evaporation through micro-explosions. Nevertheless, in many cases, a second particle mode with sizes of a few hundred nanometers is formed. In this paper, we investigate two possible reasons for the appearance of large particles. Firstly, we analyze the effect of the oxygen dispersion gas flow applied in the two-fluid nozzle on the droplet size distributions of burning sprays using phase Doppler anemometry. We identified that an increase of the dispersion gas flow significantly decreases the number concentration of large droplets (>30 μm), which causes a significant increase of the BET surface area of as-synthesized LaMnO3 and LaCoO3 with increasing dispersion gas flow from 60 m2/g (5 slm dispersion gas) to 100 m2/g (8 slm). Secondly, the esterification in the mixture of solvents towards ethyl-2-ethylhexanoate, which is associated with the release of water as a byproduct, was analyzed by GC/MS. The ester concentration in the iron-containing solution was found to be up to nine times higher than in cobalt or manganese precursor solutions. Simultaneously, the produced LaFeO3 materials show lower BET surface areas and the increasing dispersion gas flow has a minor effect on this material than on the cobalt and manganese perovskite cases. We attribute this to the fact that water formed during esterification forces the hydrolysis of iron nitrate and the formation of large particles within the droplets. © 2020 The Combustion Institute.
view abstract doi: 10.1016/j.proci.2020.07.116 2020 • 343 Synergistic Effect of Molybdenum and Tungsten in Highly Mixed Carbide Nanoparticles as Effective Catalysts in the Hydrogen Evolution Reaction under Alkaline and Acidic Conditions
Fu, Q. and Peng, B. and Masa, J. and Chen, Y.-T. and Xia, W. and Schuhmann, W. and Muhler, M.
ChemElectroChem 7 983-988 (2020)Monometallic Mo and W carbides as well as highly mixed (Mo,W) carbides with various Mo/W ratios were synthesized directly on oxygen-functionalized carbon nanotubes (OCNTs), and used as noble-metal-free electrocatalysts in the hydrogen evolution reaction (HER) under both acidic and alkaline conditions. A purely orthorhombic structure was found in both monometallic and mixed carbide samples by X-ray diffraction. Transmission electron microscopy images showed that the carbide particles were highly dispersed on the OCNTs with well-controlled particle size. The homogeneous distribution of Mo and W in the carbides was confirmed by elemental mapping. (Mo,W)2C/OCNT with a Mo/W ratio of 3 : 1 showed the lowest overpotential to reach a current density of 10 mA/cm2 (87 mV in 0.1 M KOH and 92 mV in 0.5 M H2SO4), and the smallest Tafel slope of 34 mV/dec. Long-term stability under both alkaline and acidic conditions was demonstrated for 24 h. Our results revealed that an optimal amount of W in the mixed carbide can significantly improve its performance in the HER following the Tafel reaction pathway, most likely due to the weakened Mo−Hads bond. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
view abstract doi: 10.1002/celc.202000047 2020 • 342 Synthesis and characterization of PLGA/HAP scaffolds with DNA-functionalised calcium phosphate nanoparticles for bone tissue engineering
Sokolova, V. and Kostka, K. and Shalumon, K.T. and Prymak, O. and Chen, J.-P. and Epple, M.
Journal of Materials Science: Materials in Medicine 31 (2020)Porous scaffolds of poly(lactide-co-glycolide) (PLGA; 85:15) and nano-hydroxyapatite (nHAP) were prepared by an emulsion-precipitation procedure from uniform PLGA–nHAP spheres (150–250 µm diameter). These spheres were then thermally sintered at 83 °C to porous scaffolds that can serve for bone tissue engineering or for bone substitution. The base materials PLGA and nHAP and the PLGA–nHAP scaffolds were extensively characterized by X-ray powder diffraction, infrared spectroscopy, thermogravimetry, differential scanning calorimetry, and scanning electron microscopy. The scaffold porosity was about 50 vol% as determined by relating mass and volume of the scaffolds, together with the computed density of the solid phase (PLGA–nHAP). The cultivation of HeLa cells demonstrated their high cytocompatibility. In combination with DNA-loaded calcium phosphate nanoparticles, they showed a good activity of gene transfection with enhanced green fluorescent protein (EGFP) as model protein. This is expected enhance bone growth around an implanted scaffold or inside a scaffold for tissue engineering. [Figure not available: see fulltext.] © 2020, The Author(s).
view abstract doi: 10.1007/s10856-020-06442-1 2020 • 341 The Influence of the Distribution Function of Ferroelectric Nanoparticles Sizes on Their Electrocaloric and Pyroelectric Properties
Shevliakova, H.V. and Morozovska, A.N. and Morozosky, N.V. and Svechnikov, G.S. and Shvartsman, V.V.
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 67 2445-2453 (2020)We consider a model of a nanocomposite based on noninteracting spherical single-domain ferroelectric nanoparticles (NPs) of various sizes embedded in a dielectric matrix. The size distribution function of these NPs is selected as a part of the truncated Gaussian distribution from minimum to maximum radius. For such nanocomposites, we calculate the dependences of the reversible part of the electric polarization, the electrocaloric (EC) temperature change, and the dielectric permittivity on the external electric field, which have the characteristic form of hysteresis loops. We then analyze the change in the shape of the hysteresis loops relative to the particle size distribution parameters. We demonstrate that the remanent polarization, coercive field, dielectric permittivity maximums, and maximums and minimums of the EC temperature change depend most strongly on the most probable radius, moderately on the dispersion, and have the weakest dependence on the maximum radius of the NP. We calculate and analyze the dependences of pyroelectric figures of merit on the average radius of the NPs in the composite. The dependences confirm the presence of a phase transition induced by the size of the NPs, which is characterized by the presence of a maxima near the critical average radius of the particles, the value of which increases with an increasing dispersion of the distribution function. © 1986-2012 IEEE.
view abstract doi: 10.1109/TUFFC.2020.3004740 2019 • 340 Application of Raman spectroscopy to the flotation process of fluorite
Lewandowski, B. and Said, B.B. and Ulbricht, M. and Krekel, G.
Minerals Engineering 135 129-138 (2019)Exact knowledge of the content of the various components in a flotation system is critical in both product analysis and process control. In the present work, FT Raman spectroscopy was successfully applied to an industrial fluorite flotation system for quantification of calcium fluoride (CaF 2 ). In a first step, an artificial model system consisting of CaF 2 , barium sulphate and silica was set up to test feasibility of FT Raman spectroscopy and to generate a calibration curve. An empirical model was developed, which incorporates effects of particle size on Raman shift and peak area, so that a CaF 2 quantification is feasible independent of particle size. Conversely, the empirical model provides information about the approximate particle size in the analysed sample. A cross-validation using X-ray fluorescence spectroscopy showed excellent quantification of CaF 2 in seven industrial fluorite samples with CaF 2 weight fraction in a range from 7% to 98% with absolute differences of less than 5%. In a first laboratory batch-flotation experiment, the CaF 2 content of the froth product could be quantified successfully providing additional information about the approximate median particle size of the concentrate, making FT Raman spectroscopy superior to commonly applied X-ray fluorescence spectroscopy. © 2019 Elsevier Ltd
view abstract doi: 10.1016/j.mineng.2019.02.038 2019 • 339 Calcium phosphate nanoparticle-mediated transfection in 2D and 3D mono- and co-culture cell models
Sokolova, V. and Rojas-Sánchez, L. and Białas, N. and Schulze, N. and Epple, M.
Acta Biomaterialia 84 391-401 (2019)The transfer of nucleic acids into living cells, i.e. transfection, is a major technique in current molecular biology and medicine. As nucleic acids alone are not able to penetrate the cell membrane, an efficient carrier is needed. Calcium phosphate nanoparticles can serve as carrier due to their biocompatibility, biodegradability and high affinity to nucleic acids like DNA or RNA. Their application was extended here from two-dimensional (2D) to three-dimensional (3D) cell culture models, including co-cultures. Compared to 2D monolayer cell cultures, a 3D culture system represents a more realistic spatial, biochemical and cellular environment. The uptake of fluorescent calcium phosphate nanoparticles (diameter 40–70 nm; cationic) was studied in 2D and 3D cell culture models by confocal laser scanning microscopy. The transfection of eGFP by calcium phosphate nanoparticles was compared in 2D and 3D cell culture, including co-cultures of green fluorescing HeLa-eGFP cells and MG-63 cells in 2D and in 3D models with the red fluorescent protein mCherry. This permitted a cell-specific assessment of the local transfection efficiency. In general, the penetration of nanoparticles into the spheroids was significantly higher than that of a model oligonucleotide carried by Lipofectamine. The transfection efficiency was comparable in 3D cell cultures with 2D cell cultures, but it occurred preferentially at the surface of the spheroids, following the uptake pathway of the nanoparticles. Statement of significance: Three-dimensional cell culture models can serve as a bridge between the in-vitro cell cultures and the in-vivo situation, especially when mass transfer effects have to be considered. This is the case for nanoparticles where the incubation effect in a two-dimensional cell culture strongly differs from a three-dimensional cell culture or a living tissue. We have compared the uptake of nanoparticles and a subsequent transfection of fluorescent proteins in two-dimensional and three-dimensional cell culture models. An elegant model to investigate the transfection in co-cultures was developed using HeLa-eGFP cells (green fluorescent) together with MG-63 cells (non-fluorescent) that were transfected with the red-fluorescing protein mCherry. Thereby, the transfection of both cell types in the co-culture was easily distinguished. © 2018 Acta Materialia Inc.
view abstract doi: 10.1016/j.actbio.2018.11.051 2019 • 338 Control of Metal–Organic Framework Crystallization by Metastable Intermediate Pre-equilibrium Species
Yeung, H.H.M. and Sapnik, A.F. and Massingberd-Mundy, F. and Gaultois, M.W. and Wu, Y. and Fraser, D.A.X. and Henke, S. and Pallach, R. and Heidenreich, N. and Magdysyuk, O.V. and Vo, N.T. and Goodwin, A.L.
Angewandte Chemie - International Edition 58 566-571 (2019)There is an increasing amount of interest in metal–organic frameworks (MOFs) for a variety of applications, from gas sensing and separations to electronics and catalysis. However, the mechanisms by which they crystallize remain poorly understood. Herein, an important new insight into MOF formation is reported. It is shown that, prior to network assembly, crystallization intermediates in the canonical ZIF-8 system exist in a dynamic pre-equilibrium, which depends on the reactant concentrations and the progress of reaction. Concentration can, therefore, be used as a synthetic handle to directly control particle size, with potential implications for industrial scale-up and gas sorption applications. These findings enable the rationalization of apparent contradictions between previous studies of ZIF-8 and opens up new opportunities for the control of crystallization in network solids more generally. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract doi: 10.1002/anie.201810039 2019 • 337 Development of a high flow rate aerodynamic lens system for inclusion of nanoparticles into growing PVD films to form nanocomposite thin films
Kiesler, D. and Bastuck, T. and Kennedy, M.K. and Kruis, F.E.
Aerosol Science and Technology 53 630-646 (2019)Hard coatings for wear protection of tools, bearings, and sliding parts play an important role in industrial manufacturing. Nanocomposite coatings are being used in this context to improve the mechanical properties. The technology applied therefore is often based on physical vapor deposition (PVD), in which the different materials are co-deposited. In these processes it is not possible to control the properties of the disperse phase and continuous phase independently. Here, we present a technology which combines aerosol technology with thin film technology to produce nanocomposite coatings directly, which gives us full control over both phases. It is based on an upscaled three-stage aerodynamic lens, which allows to bring nanoparticles from an atmospheric-pressure aerosol reactor into a PVD vacuum chamber operating at low pressure (2 Pa). This requires the use of a higher mass flow rate than conventionally used in aerodynamic lenses, so that a rational upscaling strategy for designing an aerodynamic lens for larger mass flow rates is proposed. Here, an array consisting of eight parallel three-stage aerodynamic lenses having each a mass flow rate of 0.6 slm using argon and 0.71 slm using nitrogen is built and optimized, assisted by CFD and numerical trajectory analysis. The transfer efficiency has been investigated numerically and experimentally. It is possible to transfer 80% of the particles with only 1.3% of the gas into the deposition chamber. A number of coatings consisting of titanium carbonitride nanoparticles embedded in a PVD chromium oxynitride film with varying nanoparticle content were produced. Electron microscopy shows the successful incorporation of the nanoparticles in the thin film. A reduction in film crystallite size with increasing nanoparticle content was found. A reverse Hall–Petch behavior was observed. Copyright © 2019 American Association for Aerosol Research. © 2019, © 2019 American Association for Aerosol Research.
view abstract doi: 10.1080/02786826.2019.1587149 2019 • 336 Electrostatic precipitation of submicron particles in a molten carrier
Dobrowolski, A. and Pieloth, D. and Wiggers, H. and Thommes, M.
Pharmaceutics 11 (2019)Recently, submicron particles have been discussed as a means to increase the bioavailability of poorly water-soluble drugs. Separation of these small particles is done with both fibre and membrane filters, as well as electrostatic precipitators. A major disadvantage of an electrostatic precipitator (ESP) is the agglomerate formation on the precipitation electrode. These agglomerates frequently show low bioavailability, due to the decreased specific surface area and poor wettability. In this work, a new melt electrostatic precipitator was developed and tested to convert submicron particles into a solid dispersion in order to increase the bioavailability of active pharmaceutical ingredients. The submicron particles were generated by spray drying and transferred to the ESP, where the collection electrode is covered with a melt, which served as matrix after solidification. The newly developed melt electrostatic precipitator was able to collect isolated naproxen particles in a molten carrier. A solid naproxen xylitol dispersion was prepared, which showed a reduction of the dissolution time by 82%, and a release of 80% of the total drug, compared to the physical mixture. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.
view abstract doi: 10.3390/pharmaceutics11060276 2019 • 335 Engineering atomic-level complexity in high-entropy and complex concentrated alloys
Oh, H.S. and Kim, S.J. and Odbadrakh, K. and Ryu, W.H. and Yoon, K.N. and Mu, S. and Körmann, F. and Ikeda, Y. and Tasan, C.C. and Raabe, D. and Egami, T. and Park, E.S.
Nature Communications 10 (2019)Quantitative and well-targeted design of modern alloys is extremely challenging due to their immense compositional space. When considering only 50 elements for compositional blending the number of possible alloys is practically infinite, as is the associated unexplored property realm. In this paper, we present a simple property-targeted quantitative design approach for atomic-level complexity in complex concentrated and high-entropy alloys, based on quantum-mechanically derived atomic-level pressure approximation. It allows identification of the best suited element mix for high solid-solution strengthening using the simple electronegativity difference among the constituent elements. This approach can be used for designing alloys with customized properties, such as a simple binary NiV solid solution whose yield strength exceeds that of the Cantor high-entropy alloy by nearly a factor of two. This study provides general design rules that enable effective utilization of atomic level information to reduce the immense degrees of freedom in compositional space without sacrificing physics-related plausibility. © 2019, The Author(s).
view abstract doi: 10.1038/s41467-019-10012-7 2019 • 334 Evolution of the Ligand Shell Around Small ZnO Nanoparticles During the Exchange of Acetate by Catechol: A Small Angle Scattering Study
Schindler, T. and Lin, W. and Schmutzler, T. and Lindner, P. and Peukert, W. and Segets, D. and Unruh, T.
ChemNanoMat 5 116-123 (2019)The core-shell structure of colloids surrounded by ligands is of great importance for their later application as it can significantly alter the chemical and physical properties of the nanoparticles (NPs). A combination of small angle X-ray and neutron scattering (SAXS/SANS) in the native solution with additional ex situ measurements (titration-UV) was applied to study the NP/ligand interface of ZnO NPs after functionalization with catechol derivatives. Based on SAXS data, it was found that within the multimodal particle size distribution the fraction of agglomerates is shifted to smaller sizes and nearly disappeared upon the binding of ethyl 3,4-dihydroxybenzoate (CAT) molecules. This is ascribed to improved stabilization at the primary particle level by CAT molecules. By combining the neutron scattering contrast with the input of bound CAT molecules from a previously developed titration-UV method, the heterogeneous composition of the ligand shell became accessible for the first time. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract doi: 10.1002/cnma.201800465 2019 • 333 Fragmentation of pulverized coal in a laminar drop tube reactor: Experiments and model
Senneca, O. and Heuer, S. and Bareschino, P. and Urciuolo, M. and Pepe, F. and Schiemann, M. and Chirone, R. and Scherer, V.
Proceedings of the Combustion Institute 37 2849-2855 (2019)Fragmentation during pulverized coal particles conversion shifts the particle size distribution of the fuel towards smaller particle sizes, affecting both conversion rates and heat release. After pyrolysis of a high volatiles Colombian coal in CO2 atmosphere in a drop tube reactor at 1573 K, solid carbonaceous particles of different size, from 100 μm of the particle feed down to the nanometric size, have been observed. A fragmentation model has been used to predict the fate of Colombian coal particles under the experimental conditions of the drop tube experiment and predict the particle size distribution (PSD). Model and experimental results are in very good agreement and indicate that in the DTR experiment the coal underwent almost complete pyrolysis and that fragmentation generated a 36 wt% population of particles with size close to 30 μm. The close match between the PSDs obtained from experiments and from the fragmentation model is an important novelty. It demonstrates that fragmentation occurs not only under fluidized bed conditions but also under the conditions of pulverized coal combustion. Experimentalists are warned against the fact that the fine particulate sampled at the outlet of laminar flow reactors and boilers is not always composed of soot only. Char fragments can be misidentified as soot. The implementation of fragmentation submodels in pulverized fuel combustion and gasification codes is highly recommended. © 2018 The Combustion Institute.
view abstract doi: 10.1016/j.proci.2018.08.057 2019 • 332 High-surface-area corundum by mechanochemically induced phase transformation of boehmite
Amrute, A.P. and Łodziana, Z. and Schreyer, H. and Weidenthaler, C. and Schüth, F.
Science 366 485-489 (2019)In its nanoparticulate form, corundum (a-Al2O3) could lead to several applications. However, its production into nanoparticles (NPs) is greatly hampered by the high activation energy barrier for its formation from cubic close-packed oxides and the sporadic nature of its nucleation. We report a simple synthesis of nanometer-sized a-Al2O3 (particle diameter ~13 nm, surface areas ~140 m2 g-1) by the mechanochemical dehydration of boehmite (g-AlOOH) at room temperature. This transformation is accompanied by severe microstructural rearrangements and might involve the formation of rare mineral phases, diaspore and tohdite, as intermediates. Thermodynamic calculations indicate that this transformation is driven by the shift in stability from boehmite to a-Al2O3 caused by milling impacts on the surface energy. Structural water in boehmite plays a crucial role in generating and stabilizing a-Al2O3 NPs. © 2019 American Association for the Advancement of Science. All rights reserved.
view abstract doi: 10.1126/science.aaw9377 2019 • 331 How the re-irradiation of a single ablation spot affects cavitation bubble dynamics and nanoparticles properties in laser ablation in liquids
Letzel, A. and Santoro, M. and Frohleiks, J. and Ziefuß, A.R. and Reich, S. and Plech, A. and Fazio, E. and Neri, F. and Barcikowski, S. and Gökce, B.
Applied Surface Science 473 828-837 (2019)Fundamental theoretical and experimental studies on the formation of nanoparticles and cavitation during laser synthesis of colloids usually employ single-pulse conditions, whereas studies of the properties of nanoparticles naturally require prolonged ablation. We explored how a defined number of pulses changes a silver target's surface geometry and thereby the dynamics of the laser-induced cavitation bubble and the resulting properties of the nanoparticles. The shape of the cavitation bubble transforms from hemispherical to almost spherical. The indirectly calculated mass concentration in the cavitation bubble follows a decay with the number of laser pulses. Surprisingly, the ablated mass does not set the volume of the extended cavitation bubble, as one would expect, because of the linear dependency of both the volume of the bubble and the ablation mass per pulse on the laser fluence. No influence of the altered cavitation bubble on the nanoparticles was identified. Instead, clear evidence of a high share of silver nanoclusters (d < 3 nm) with improved instrumentation (ultracentrifuge) was found in all samples at our low concentration conditions. The influence of these reactive species on the final particle size was found to be much larger than the cavitation bubble variations caused by prolonged surface ablation. In addition, no correlation was observed between the size of the primary particles (∼8 nm) and the mass concentration in the cavitation bubble. © 2018
view abstract doi: 10.1016/j.apsusc.2018.12.025 2019 • 330 Influence of etching-pretreatment on nano-grained WC-Co surfaces and properties of PVD/HVOF duplex coatings
Tillmann, W. and Hagen, L. and Stangier, D. and Krabiell, M. and Schröder, P. and Tiller, J. and Krumm, C. and Sternemann, C. and Paulus, M. and Elbers, M.
Surface and Coatings Technology 374 32-43 (2019)The deposition of coatings by means of Physical Vapor Deposition (PVD)is an established process to enhance the lifetime and performance of carbide bulk tools. Although the effect of surface pretreatments on conventional WC-Co surfaces is well known, this investigation examines for the first time, how different surface pretreatments affect the surface integrity of thermally sprayed WC-Co substrates prior a subsequent PVD layer deposition and its resulting properties. Therefore, a WC-12Co feedstock with an average WC particle size of 100 nm was thermally sprayed on AISI M3 steel substrates using High Velocity Oxy-Fuel (HVOF)technique. Hereinafter, the HVOF sprayed WC-Co coatings were grounded and polished, thus serving as substrates for further surface pretreatments and the deposition of a CrAlN PVD hard coating by means of magnetron sputtering. To evaluate the influence of various surface pretreatments on the HVOF sprayed WC-Co coatings, several sequences such as heating, inert gas ion etching, metal ion etching, and High Power Impulse Magnetron Sputtering (HIPIMS)-etching were carried out. With respect to the subsequent PVD layer deposition, the results show that the pretreatment does neither affect the hardness nor Young's modulus of the CrAlN top layer. Yet, different effects on the WC-Co surface and PVD coating adhesion are observed. Inert gas ion etching leads to a faster removal of the carbides than of the Co-binder matrix. In contrast, metal ion etching provides a “micro-blasting” effect and removes the binder matrix as verified by Atomic Force Microscope (AFM)measurements. As a result, a decrease of the compressive residual stress state and an increase of the surface free energy are observed. With respect to HIPIMS-etching, a Cr-nanolayer was applied onto the WC-Co surface, which enhances the adhesion of the CrAlN top layer. Nevertheless, HRC Rockwell adhesion and scratch tests reveal a superior adhesion for samples pretreated with the metal ion etching. © 2019 Elsevier B.V.
view abstract doi: 10.1016/j.surfcoat.2019.05.054 2019 • 329 Influence of flow alterations on bacteria retention during microfiltration
Helling, A. and Grote, C. and Büning, D. and Ulbricht, M. and Wessling, M. and Polakovic, M. and Thom, V.
Journal of Membrane Science 575 147-159 (2019)Microfiltration membranes retain bacteria predominantly by size-exclusion. However, some empirical data points towards the fact, that alterations in flow rate as well as changes in the quality of adhesive interactions between the membrane surface and the bacteria can affect their retention. For parvo virus retaining normal flow virus-filters, systematic investigations have been undertaken to characterize the impact of flow alterations as well as modulations of particle-membrane interactions on virus particle retention. For depth filters used, e.g., for the clarification of fermentation broths, it is well known that alterations in flow rate typically lead to elevated levels of turbidity. This work adopts the acquired knowledge from virus- and depth-filters and investigates their applicability for bacteria retention by microfiltration membranes. It presents particle retention data for mycoplasma and Gram-negative and Gram-positive bacteria. Single layer flat sheet PES model microfiltration membranes with maximum pore sizes varying from 0.3 to 1.5 µm and an overall low retention were used in order to easily detect and differentiate their retention properties for the different particle species. The event of particle breakthrough is elucidated depending on the adsorptive character of the membrane surface, the pore size, and changes in flow rate including the interruption of flow. Moreover, this work investigates how the chemical and physical solution properties influence bacterial retention. These properties include the temperature of the fluid, the presence of a surfactant, the salt concentration and the pH. Flow interruptions using B. diminuta were also applied to commercially available PES sterilizing-grade microfiltration membranes showing no bacterial breakthrough. © 2019 Elsevier B.V.
view abstract doi: 10.1016/j.memsci.2019.01.021 2019 • 328 Investigation of HVOF-ID spraying with WC-CoCr-155 μm feedstock powder
Tillmann, W. and Schaak, C. and Hagen, L. and Dildrop, M.
IOP Conference Series: Materials Science and Engineering 480 (2019)High velocity oxygen fuel (HVOF) spraying of WC-Co(Cr) with different chemical compositions, different powder size fractions, and different mean carbide sizes is a well-established research field for outer diameter (OD) applications. These coatings are typically applied as wear protective layers for different types of industries. Current demands for internal diameter (ID) coatings lead to a great interest in HVOF-ID spraying. This field of application necessitates a special spray gun equipment and spray powders with particle size fractions smaller than 20 μm. At the same time, the process control concerning both the spray gun configuration and the use of fine powders leads to new challenges which differ from those of OD HVOF spraying. In this study, HVOF-ID spraying using a WC-CoCr 86-10-4 (-155 μm) feedstock with a mean WC particle size of 400 nm is investigated with respect to the resulting coating properties. A statistical design of experiments (DoE) is utilized to enable a systematic analysis of various process parameter settings along with their interaction on the microstructural characteristics as well as the deposition efficiency (DE). Based on the results, a desirability-based multi-criteria optimization is carried out in order to produce adequate coating properties. The obtained knowledge about the spray system enables to realize dense WC-CoCr coatings with a porosity of approximately 1 %. © Published under licence by IOP Publishing Ltd.
view abstract doi: 10.1088/1757-899X/480/1/012008 2019 • 327 Modular Pd/Zeolite Composites Demonstrating the Key Role of Support Hydrophobic/Hydrophilic Character in Methane Catalytic Combustion
Losch, P. and Huang, W. and Vozniuk, O. and Goodman, E.D. and Schmidt, W. and Cargnello, M.
ACS Catalysis 9 4742-4753 (2019)Complete catalytic oxidation of methane in the presence of steam at low temperatures (T < 400 °C) is a crucial reaction for emission control, yet it presents profound challenges. The activation of the strong C-H bond of methane at low temperature is difficult, and the water present in any realistic application poisons the active surface and promotes sintering of Pd particles during the reaction. Finding materials that can deliver high reaction rates while being more resistant to the presence of water is imperative for advancing several technological applications of natural gas-based systems. However, methods to fairly compare the activity of Pd catalysts (the most active metal for methane combustion) are needed in order to perform useful structure-property relationship studies. Here, we report a method to study how zeolite hydrophobicity affects the activity of Pd nanoparticles in the reaction, which led to a significant improvement in the water resistance. Mesoporous zeolites were synthesized starting from commercially available microporous zeolites. In this way, a variety of hierarchically porous zeolites, with different hydrophobic/hydrophilic character, were prepared. Preformed colloidal Pd nanoparticles could be deposited within mesostructured zeolites. This approach enabled the systematic study of key parameters such as zeolite framework, Al content, and the Pd loading while maintaining the same Pd particle size and structure for all the samples. Detailed catalytic studies revealed an optimum hydrophobic/hydrophilic character, and a promising steam-resistant catalyst, namely, 3.2 nm Pd particles supported on mesoporous zeolite beta or USY with a Si/Al ratio of 40, emerged from this multiparametric study with a T50 of 355 °C and T90 of 375 °C (where T50 and T90 are temperature values at which the samples reach 50% and 90% methane conversion, respectively) in steam-containing reaction conditions. Finally, we verified that the designed catalysts were stable by in-depth postcatalysis characterization and operando diffuse-reflectance infrared Fourier-transform spectroscopy (DRIFTS) analyses confirming that water adsorbs less strongly on the active PdO surface due to interaction with the zeolite acid sites. This method can be of general use to study how zeolite supports affect the reactivity of supported metals in several catalytic applications. © 2019 American Chemical Society.
view abstract doi: 10.1021/acscatal.9b00596 2019 • 326 Non-monotonic effect of additive particle size on the glass transition in polymers
Zirdehi, E.M. and Varnik, F.
Journal of Chemical Physics 150 (2019)Effect of small additive molecules on the structural relaxation of polymer melts is investigated via molecular dynamics simulations. At a constant external pressure and a fixed number concentration of added molecules, the variation of the particle diameter leads to a non-monotonic change of the relaxation dynamics of the polymer melt. For non-entangled chains, this effect is rationalized in terms of an enhanced added-particle-dynamics which competes with a weaker coupling strength upon decreasing the particle size. Interestingly, cooling simulations reveal a non-monotonic effect on the glass transition temperature also for entangled chains, where the effect of additives on polymer dynamics is more intricate. This observation underlines the importance of monomer-scale packing effects on the glass transition in polymers. In view of this fact, size-adaptive thermosensitive core-shell colloids would be a promising candidate route to explore this phenomenon experimentally. © 2019 Author(s).
view abstract doi: 10.1063/1.5063476 2019 • 325 Numerical Study on Particle–Gas Interaction Close to the Substrates in Thermal Spray Processes with High-Kinetic and Low-Pressure Conditions
Journal of Thermal Spray Technology 28 27-39 (2019)In thermal spray processes, the interaction between the gas jet and the particulate feedstock can affect the coating build-up mechanisms considerably. In particular under high-kinetic and low-pressure conditions, small particles are subjected to rapid deflection and velocity changes close to the substrate. In this work, numerical studies were carried out to investigate the interaction between gas and particles in the substrate boundary layers (BL). Typical conditions for suspension plasma spraying (SPS), plasma spray-physical vapor deposition (PS-PVD), and aerosol deposition (AD) were taken as a basis. Particular importance was attached to the consideration of rarefaction and compressibility effects on the drag force. Typical Stokes numbers for the different thermal spray processes were calculated and compared. Possible effects on the resulting coating build-up mechanisms and microstructure formation are discussed. The results show that just for larger particles in the SPS process the laminar flow attached to the particles begins to separate so that the drag coefficients have to be corrected. Furthermore, slip effects occur in all the investigated processes and must be considered. The comparison of calculated Stokes numbers with critical values shows that there is a disposition to form columnar microstructures or stacking effects depending on the particle size for PS-PVD and SPS, but not for AD. © 2018, ASM International.
view abstract doi: 10.1007/s11666-018-0810-3 2019 • 324 Perforating Freestanding Molybdenum Disulfide Monolayers with Highly Charged Ions
Kozubek, R. and Tripathi, M. and Ghorbani-Asl, M. and Kretschmer, S. and Madauß, L. and Pollmann, E. and O'Brien, M. and McEvoy, N. and Ludacka, U. and Susi, T. and Duesberg, G.S. and Wilhelm, R.A. and Krasheninnikov, A.V. and Ko...
Journal of Physical Chemistry Letters 10 904-910 (2019)Porous single-layer molybdenum disulfide (MoS 2 ) is a promising material for applications such as DNA sequencing and water desalination. In this work, we introduce irradiation with highly charged ions (HCIs) as a new technique to fabricate well-defined pores in MoS 2 . Surprisingly, we find a linear increase of the pore creation efficiency over a broad range of potential energies. Comparison to atomistic simulations reveals the critical role of energy deposition from the ion to the material through electronic excitation in the defect creation process and suggests an enrichment in molybdenum in the vicinity of the pore edges at least for ions with low potential energies. Analysis of the irradiated samples with atomic resolution scanning transmission electron microscopy reveals a clear dependence of the pore size on the potential energy of the projectiles, establishing irradiation with highly charged ions as an effective method to create pores with narrow size distributions and radii between ca. 0.3 and 3 nm. © 2019 American Chemical Society.
view abstract doi: 10.1021/acs.jpclett.8b03666 2019 • 323 Perspective of Surfactant-Free Colloidal Nanoparticles in Heterogeneous Catalysis
Reichenberger, S. and Marzun, G. and Muhler, M. and Barcikowski, S.
ChemCatChem 11 4489-4518 (2019)Due to material gaps and synthesis-related cross-correlations in heterogeneous catalysis, chemists and physicists are constantly motivated to develop novel catalyst preparation methods for independent control of morphology, size, and composition. Within this article, advances, opportunities, and the current limits of laser-based catalyst preparation technique, as well as synergies with conventional methods will be reviewed in terms of purity, particle size, morphology, composition, and nanoparticle-support interaction. It will be shown, that the surfactant-free particles represent ideal model materials to validate kinetic models and conduct parametric activity studies by independent adjustment of functional properties like nanoparticle size, composition, and load. Consequently, the importance of transient plasma dynamics tailoring nanoparticle formation will be pointed out, comparing experimental studies with own calculations and novel simulations taken from literature. Finally, perspectives of surfactant-free colloidal nanoparticles for unrevealing active sites in heterogeneous catalysts are presented. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract doi: 10.1002/cctc.201900666 2019 • 322 Platinum nanoparticles supported on reduced graphene oxide prepared in situ by a continuous one-step laser process
Haxhiaj, I. and Tigges, S. and Firla, D. and Zhang, X. and Hagemann, U. and Kondo, T. and Nakamura, J. and Marzun, G. and Barcikowski, S.
Applied Surface Science 469 811-820 (2019)A large research emphasis is still placed on improvement of production routes of nanosized materials with enhanced catalytic properties. Here we developed a continuous process for generation of platinum (Pt) nanoparticles supported on reduced graphene oxide (rGO) in situ via pulsed laser ablation in liquid (PLAL) dispersion of rGO. This in situ PLAL technique is a single step procedure that allows the synthesis of heterogeneous catalysts with a simultaneous control of particle size and mass loading. By this method, Pt particles with mean particle diameters around 2.5 nm and in a regime of 3–4 nm have been produced in ethanol and saline water, respectively, and adsorbed on rGO with up to 50 wt%. Both inorganic and organic solvents used during in situ synthesis lead to production of CO tolerant Pt/rGO catalysts, which are relevant for fuel cell applications due to the remarkably low CO desorption temperatures around 65–80 °C. © 2018 Elsevier B.V.
view abstract doi: 10.1016/j.apsusc.2018.10.257 2019 • 321 Scalable classification of nanoparticles: A proof of principle for process design
Menter, C. and Segets, D.
Advanced Powder Technology 30 2801-2811 (2019)Nanoparticles like quantum confined ZnS semiconductor nanocrystals, exhibit unique structure-property relationships. Narrow particle size distributions (PSDs) become one of the most important factors to tailor product performance. Size selective precipitation has already been proven to be an effective post processing strategy for ZnS nanoparticles. It is based on the titration of a poor liquid into a stable dispersion, which leads to the preferred flocculation of larger particles. Afterwards, these flocks must be separated from the continuous phase. While on lab scale the formed flocks can be easily separated by centrifugation from the fine fraction, for larger scale production using continuous processes, new concepts are urgently needed. Herein we developed a filtration process for flock removal that allows the handling of larger quantities. For process design, we first investigated the flock properties in order to know how stable the generated flocks are and how the flock properties can be controlled. Then, we replaced the classical flock separation by centrifugation through separation by surface filtration under the constraint that the underlying separation efficiency was not affected. By the future use of properly controlled, alternating filtration modules, our work opens the door for establishing an urgently needed, scalable post-processing for sub-10 nm nanoparticles. © 2019 Society of Powder Technology Japan
view abstract doi: 10.1016/j.apt.2019.08.027 2019 • 320 Scale-up of the rounding process in pelletization by extrusion-spheronization
Evers, M. and Weis, D. and Antonyuk, S. and Thommes, M.
Pharmaceutical Development and Technology 24 1014-1020 (2019)Previously described scaling models for the spheronization process of wet extrudates are incomplete, often concluding with an adjustment of the plate speed according to the spheronizer diameter, but neglecting to give guidelines on the adjustment of the load or the process duration. In this work, existing scaling models were extended to include the load and the process time. By analyzing the final particle size and shape distributions as well as the rounding kinetics for various loads and plate speeds in spheronizers with plate diameters of 0.12 m, 0.25 m and 0.38 m, the found scaling model was validated. The peripheral speed was found to be the main influence on the rounding kinetic, while the load and the plate diameter only showed minor influence. Higher peripheral speeds, higher loads and a larger spheronizer diameter led to an increase in rounding kinetic, allowing for shorter residence times and increased throughput. However, lower peripheral speed, lower loads and lower plate diameters led to particles of increased sphericity. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.
view abstract doi: 10.1080/10837450.2019.1621900 2019 • 319 Sensitive and selective detection of Cu2+ ions based on fluorescent Ag nanoparticles synthesized by R-phycoerythrin from marine algae Porphyra yezoensis
Xu, Y. and Hou, Y. and Wang, Y. and Wang, Y. and Li, T. and Song, C. and Wei, N. and Wang, Q.
Ecotoxicology and Environmental Safety 168 356-362 (2019)In this study, using a natural and green protein R-phycoerythrin (R-PE) extracted from marine Porphyra yezoensis as the stabilizer and reducer, silver nanoparticles (AgNPs) were synthesized. Based on this, a highly sensitive and selective method for the detection of Cu2+ ions was developed using R-PE-AgNPs as fluorescent probe. The interactions between R-PE-AgNPs and Cu2+ ions were systematically characterized by fluorescence spectroscopy, transmission electron microscopy (TEM), elemental mapping and Fourier transform infrared (FTIR). It was found that Cu2+ ions could cause aggregation of the R-PE-AgNPs, accompanied by the greatly increased particle size. Importantly, the method offered a wide linear detection range from 0 μM to 100.0 μM with a detection limit of 0.0190 μM. Moreover, the proposed method was successfully applied to analyze Cu2+ ions in tap water and lake water samples, acquiring satisfactory recovery between 91.6% and 102.2%. Such a green, fast and cost-effective fluorimetric method of the R-PE-AgNPs probe has great potential for tracing Cu2+ ions in diverse aqueous media. © 2018 Elsevier Inc.
view abstract doi: 10.1016/j.ecoenv.2018.10.102 2019 • 318 Size effects on rotational particle diffusion in complex fluids as probed by Magnetic Particle Nanorheology
Hess, M. and Roeben, E. and Rochels, P. and Zylla, M. and Webers, S. and Wende, H. and Schmidt, A.M.
Physical Chemistry Chemical Physics 21 26525-26539 (2019)Rheological approaches based on micro- or nanoscopic probe objects are of interest due to the low volume requirement, the option of spatially resolved probing, and the minimal-invasive nature often connected to such probes. For the study of microstructured systems or biological environments, such methods show potential for investigating the local, size-dependent diffusivity and particle-matrix interactions. For the latter, the relative length scale of the used probes compared to the size of the structural units of the matrix becomes relevant. In this study, a rotational-dynamic approach based on Magnetic Particle Nanorheology (MPN) is used to extract size- and frequency-dependent nanorheological properties by using an otherwise well-established polymer model system. We use magnetically blocked CoFe2O4 nanoparticles as tracers and systematically vary their hydrodynamic size by coating them with a silica shell. On the polymer side, we employ aqueous solutions of poly(ethylene glycol) (PEG) by varying molar mass M and volume fraction ϕ. The complex Brownian relaxation behavior of the tracer particles in solutions of systematically varied composition is investigated by means of AC susceptometry (ACS), and the results provide access to frequency dependent rheological properties. The size-dependent particle diffusivity is evaluated based on theoretical descriptions and macroscopic measurements. The results allow the classification of the investigated compositions into three regimes, taking into account the probe particle size and the length scales of the polymer solution. While a fuzzy cross-over is indicated between the well-known macroscopic behavior and structurally dominated spectra, where the hydrodynamic radius is equal to the radius of gyration of the polymer (rh ∼ Rg), the frequency-related scaling behavior is dominated by the correlation length ξ respectively by the tube diameter a in entangled solutions for rh < Rg. This journal is © the Owner Societies.
view abstract doi: 10.1039/c9cp04083h 2019 • 317 Solution NMR Spectroscopy with Isotope-Labeled Cysteine ( 13 C and 15 N) Reveals the Surface Structure of l -Cysteine-Coated Ultrasmall Gold Nanoparticles (1.8 nm)
Ruks, T. and Beuck, C. and Schaller, T. and Niemeyer, F. and Zähres, M. and Loza, K. and Heggen, M. and Hagemann, U. and Mayer, C. and Bayer, P. and Epple, M.
Langmuir 35 767-778 (2019)Ultrasmall gold nanoparticles with a diameter of 1.8 nm were synthesized by reduction of tetrachloroauric acid with sodium borohydride in the presence of l-cysteine, with natural isotope abundance as well as 13 C-labeled and 15 N-labeled. The particle diameter was determined by high-resolution transmission electron microscopy and differential centrifugal sedimentation. X-ray photoelectron spectroscopy confirmed the presence of metallic gold with only a few percent of oxidized Au(+I) species. The surface structure and the coordination environment of the cysteine ligands on the ultrasmall gold nanoparticles were studied by a variety of homo- and heteronuclear NMR spectroscopic techniques including 1 H- 13 C-heteronuclear single-quantum coherence and 13 C- 13 C-INADEQUATE. Further information on the binding situation (including the absence of residual or detached l-cysteine in the solution) and on the nanoparticle diameter (indicating the well-dispersed state) was obtained by diffusion-ordered spectroscopy ( 1 H-, 13 C-, and 1 H- 13 C-DOSY). Three coordination environments of l-cysteine on the gold surface were identified that were ascribed to different crystallographic sites, supported by geometric considerations of the nanoparticle ultrastructure. The particle size data and the NMR-spectroscopic analysis gave a particle composition of about Au 174 (cysteine) 67 . © 2018 American Chemical Society.
view abstract doi: 10.1021/acs.langmuir.8b03840 2019 • 316 Solution NMR Spectroscopy with Isotope-Labeled Cysteine (13C and 15N) Reveals the Surface Structure of l -Cysteine-Coated Ultrasmall Gold Nanoparticles (1.8 nm)
Ruks, T. and Beuck, C. and Schaller, T. and Niemeyer, F. and Zähres, M. and Loza, K. and Heggen, M. and Hagemann, U. and Mayer, C. and Bayer, P. and Epple, M.
Langmuir 35 767-778 (2019)Ultrasmall gold nanoparticles with a diameter of 1.8 nm were synthesized by reduction of tetrachloroauric acid with sodium borohydride in the presence of l-cysteine, with natural isotope abundance as well as 13C-labeled and 15N-labeled. The particle diameter was determined by high-resolution transmission electron microscopy and differential centrifugal sedimentation. X-ray photoelectron spectroscopy confirmed the presence of metallic gold with only a few percent of oxidized Au(+I) species. The surface structure and the coordination environment of the cysteine ligands on the ultrasmall gold nanoparticles were studied by a variety of homo- and heteronuclear NMR spectroscopic techniques including 1H-13C-heteronuclear single-quantum coherence and 13C-13C-INADEQUATE. Further information on the binding situation (including the absence of residual or detached l-cysteine in the solution) and on the nanoparticle diameter (indicating the well-dispersed state) was obtained by diffusion-ordered spectroscopy (1H-, 13C-, and 1H-13C-DOSY). Three coordination environments of l-cysteine on the gold surface were identified that were ascribed to different crystallographic sites, supported by geometric considerations of the nanoparticle ultrastructure. The particle size data and the NMR-spectroscopic analysis gave a particle composition of about Au174(cysteine)67. © 2018 American Chemical Society.
view abstract doi: 10.1021/acs.langmuir.8b03840 2019 • 315 Structures of carbonaceous nanoparticles formed in various pyrolysis systems
Jander, H. and Borchers, C. and Böhm, H. and Emelianov, A. and Schulz, C.
Carbon 150 244-258 (2019)In the pyrolysis of different hydrocarbon/carbon suboxid fuels formation of carbon particles with the special view to their structures was examined. For this, the following three very different pyrolysis systems were investigated experimentally i)a pyrolysis reactor, ii)a shock tube and iii)a plasma reactor with respect to the influence of varying reaction parameters on the carbonaceous nanoparticles. The particles formed in these reaction systems were studied in view of their morphology and state of crystallization by use of electron microscopy (Philips CM30)at low- and high resolution combined with micro-diffraction measurements. As to be seen at low resolution of the transmission electron microscopy studies, the particle sizes in the pyrolysis reactor and shock tube do not differ significantly, but distinguished considerably from those particle sizes obtained in the plasma reactor. While the particles obtained in the pyrolysis reactor and shock-tube had particle diameters of about d≈ 30 nm, the particles in the plasma reactor consisted of fluffy-like units, and their sizes were about d≈ 4 nm. The various carbon layers consisted of different polyaromatic hydrocarbon units with variable sizes arranged to diverse states in the course of graphitization. © 2019 Elsevier Ltd
view abstract doi: 10.1016/j.carbon.2019.02.034 2019 • 314 Synergism between Specific Halide Anions and pH Effects during Nanosecond Laser Fragmentation of Ligand-Free Gold Nanoparticles
Ziefuß, A.R. and Barcikowski, S. and Rehbock, C.
Langmuir (2019)Gold nanoclusters (AuNCs) with diameters smaller than 3 nm are an emerging field of research because they possess interesting optical properties, such as photoluminescence. However, to date, it is still difficult to distinguish whether these properties originate from the cores of the nanoparticles or from the adsorbates on their surfaces. Hence, there is a high demand for ligand-free, ultra-small particles because they make it possible to study ligand and core effects separately. Pulsed laser fragmentation in liquids (LFL) is a convenient route for the synthesis of ligand-free AuNCs. The influence of physical parameters, such as melting and evaporation, on the LFL process is well understood both theoretically and experimentally. However, the impact of the chemical composition of the medium during LFL, which critically affects the particle formation process, has been less well examined. Therefore, in this work, we elucidate the extent to which the ionic strength, the pH value, and the nature of the halide anion that is present, that is, F-, Cl-, Br-, or I-, influence the particle size distribution of the LFL product and the mean yield of small particles (<3 nm) of the product. We showed that the yield of small particles can be enhanced by the synergism between pH and specific ion effects, which probably is attributable to the adsorption of specific anions. In addition, our findings indicated that anion-based stabilization depends critically on the type of anion. A direct Hofmeister effect was observed for anions in the neutral pH regime, whereas an indirect Hofmeister series was reported in alkaline solution, which probably was due to the more hydrophilic surfaces of the AuNCs that were formed. © 2019 American Chemical Society.
view abstract doi: 10.1021/acs.langmuir.9b00418 2019 • 313 Synthesis of Mixed AuZn Nanoparticles by Spark Discharge Technique
Kala, S. and Kruis, F.E.
MRS Advances 4 1621-1629 (2019)In this study, feasibility of spark discharge technique to generate mixed metal nanoparticles is demonstrated. Two immiscible metals Au and Zn are selected to prepare AuZn mixed nanoparticles. Ignition of spark between Au and Zn electrodes under normal pressure, in the presence of carrier gas, leads to formation of mixed nanoparticles by condensation and nucleation. Online particle size-distribution is monitored by a scanning mobility particle sizer on changing carrier gas flow rate and capacitor charging current during co-sparking between Au and Zn electrodes. The technique provides flexibility to generate binary mixture of AuZn nanoparticles in the size range of 10-80 nm. Distribution of Au and Zn in the prepared mixed nanoparticles is mapped by scanning electron microscopy and high resolution electron microscopy. © Materials Research Society 2019.
view abstract doi: 10.1557/adv.2019.221 2019 • 312 Synthesis of silicon nanoparticles in a pilot-plant-scale microwave plasma reactor: Impact of flow rates and precursor concentration on the nanoparticle size and aggregation
Kunze, F. and Kuns, S. and Spree, M. and Hülser, T. and Schulz, C. and Wiggers, H. and Schnurre, S.M.
Powder Technology 342 880-886 (2019)This work is devoted to scale-up the microwave plasma synthesis of silicon nanoparticles from gaseous precursor monosilane (SiH4), previously investigated in lab-scale processes, to the pilot-plant-scale with production rates up to 200 g/h. The aim is to ensure reproducible, long-term operation of the reactor through gas-dynamic stabilization of the reacting flow and to control particle size and morphology via the gas flow velocity and the precursor concentration. Based on a newly designed nozzle, the lab-scale approach of stabilizing the plasma flow via a tangential sheath gas flow and an axial precursor gas flow was successfully transferred to the pilot-plant scale. At precursor concentrations up to 16 vol% of SiH4 diluted in argon and hydrogen, the as-synthesized particles have similar characteristics compared to those from lab-scale reactors. They are spherical, crystalline, mostly soft-agglomerated, and show a log-normal size distribution with a geometric standard deviation around 1.45 as expected for self-preserving aerosol size-distributions. In contrast to lab-scale experiments, an increase in SiH4 concentration up to 48 vol% does not lead to further growth of isolated primary particles but promotes aggregate formation from smaller primary particles. This is attributed to massive initial nucleation of very small particles due to strong supersaturation and their subsequent strong aggregation while suppressing complete coalescence due to the limited residence time at high temperature. © 2018 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2018.10.042 2019 • 311 X-ray powder diffraction to analyse bimetallic core-shell nanoparticles (gold and palladium; 7-8 nm)
Rostek, A. and Loza, K. and Heggen, M. and Epple, M.
RSC Advances 9 26628-26636 (2019)A comparative X-ray powder diffraction study on poly(N-vinyl pyrrolidone) (PVP)-stabilized palladium and gold nanoparticles and bimetallic Pd-Au nanoparticles (both types of core-shell nanostructures) was performed. The average diameter of Au and Pd nanoparticles was 5 to 6 nm. The two types of core-shell particles had a core diameter of 5 to 6 nm and an overall diameter of 7 to 8 nm, i.e. a shell thickness of 1 to 2 nm. X-ray powder diffraction on a laboratory instrument was able to distinguish between a physical mixture of gold and palladium nanoparticles and bimetallic core-shell nanoparticles. It was also possible to separate the core from the shell in both kinds of bimetallic core-shell nanoparticles due to the different domain size and because it was known which metal was in the core and which was in the shell. The spherical particles were synthesized by reduction with glucose in aqueous media. After purification by multiple centrifugation steps, the particles were characterized with respect to their structural, colloid-chemical, and spectroscopic properties, i.e. particle size, morphology, and internal elemental distribution. Dynamic light scattering (DLS), differential centrifugal sedimentation (DCS), atomic absorption spectroscopy (AAS), ultraviolet-visible spectroscopy (UV-vis), high-angle annular dark field imaging (HAADF), and energy-dispersed X-ray spectroscopy (EDX) were applied for particle characterization. This journal is © The Royal Society of Chemistry.
view abstract doi: 10.1039/c9ra05117a 2018 • 310 18F-Radiolabeling and in Vivo Analysis of SiFA-Derivatized Polymeric Core-Shell Nanoparticles
Berke, S. and Kampmann, A.-L. and Wuest, M. and Bailey, J.J. and Glowacki, B. and Wuest, F. and Jurkschat, K. and Weberskirch, R. and Schirrmacher, R.
Bioconjugate Chemistry 29 89-95 (2018)Nanoparticles represent the most widely studied drug delivery systems targeting cancer. Polymeric nanoparticles can be easily generated through a microemulsion polymerization. Herein, the synthesis, radiolabeling, and in vivo evaluation of nanoparticles (NPs) functionalized by an organosilicon fluoride acceptor (SiFA) are reported which can be radiolabeled without further chemical modifications. Four nanoparticles in the sub-100 nm range with distinct hydrodynamic diameters of 20 nm (NP1), 33 nm (NP2), 45 nm (NP3), and 72 nm (NP4), respectively, were synthesized under size-controlled conditions. The SiFA-labeling building block acted as an initiator for the polymerization of polymer P1. The nanoparticles were radiolabeled with fluorine-18 (18F) through simple isotopic exchange (IE) and analyzed in vivo in a murine mammary tumor model (EMT6). The facile 18F radiolabeling SiFA methodology, performed in ethanol under mild reaction conditions, gave radiochemical yields (RCYs) of 19-26% and specific activities (SA) of 0.2-0.3 GBq/mg. Based on preclinical PET analysis, the tumor uptake and clearance profiles were analyzed depending on particle size. The nanoparticle size of 33 nm showed the highest tumor accumulation of SUVmean 0.97 (= 4.4%ID/g) after 4 h p.i. through passive diffusion based on the Enhanced Permeability and Retention (EPR) effect. Overall, this approach exhibits a simple, robust, and reliable synthesis of 18F radiolabeled polymeric nanoparticles with a favorable in vivo evaluation profile. This approach represents a straightforward synthetically accessible alternative to produce radiolabeled nanoparticles without any further surface modification to attach a radioisotope. © 2017 American Chemical Society.
view abstract doi: 10.1021/acs.bioconjchem.7b00630 2018 • 309 A systematic electron microscopic study on the uptake of barium sulphate nano-, submicro-, microparticles by bone marrow-derived phagocytosing cells
Sokolova, V. and Loza, K. and Knuschke, T. and Heinen-Weiler, J. and Jastrow, H. and Hasenberg, M. and Buer, J. and Westendorf, A.M. and Gunzer, M. and Epple, M.
Acta Biomaterialia 80 352-363 (2018)Nanoparticles can act as transporters for synthetic molecules and biomolecules into cells, also in immunology. Antigen-presenting cells like dendritic cells are important targets for immunotherapy in nanomedicine. Therefore, we have used primary murine bone marrow-derived phagocytosing cells (bmPCs), i.e. dendritic cells and macrophages, to study their interaction with spherical barium sulphate particles of different size (40 nm, 420 nm, and 1 µm) and to follow their uptake pathway. Barium sulphate is chemically and biologically inert (no dissolution, no catalytic effects), i.e. we can separate the particle uptake effect from potential biological reactions. The colloidal stabilization of the nanoparticles was achieved by a layer of carboxymethylcellulose (CMC) which is biologically inert and gives the particles a negative zeta potential (i.e. charge). The particles were made fluorescent by conjugating 6-aminofluoresceine to CMC. Their uptake was visualized by flow cytometry, confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and correlative light and electron microscopy (CLEM). Barium sulphate particles of all sizes were readily taken up by dendritic cells and even more by macrophages, with the uptake increasing with time and particle concentration. They were mainly localized inside phagosomes, heterophagosomes, and in the case of nanoparticles also in the nearby cytosol. No particles were found in the nucleus. In nanomedicine, inorganic nanoparticles from the nanometer to the micrometer size are therefore well suited as transporters of biomolecules, including antigens, into dendritic cells and macrophages. The presented model system may also serve to describe the aseptic loosening of endoprostheses caused by abrasive wear of inert particles and the subsequent cell reaction, a question which relates to the field of nanotoxicology. Statement of Significance: The interaction of particles and cells is at the heart of nanomedicine and nanotoxicology, including abrasive wear from endoprostheses. It also comprises the immunological reaction to different kinds of nanomaterials, triggered by an immune response, e.g. by antigen-presenting cells. However, it is often difficult to separate the particle effect from a chemical or biochemical reaction to particles or their cargo. We show how chemically inert barium sulphate particles with three different sizes (nano, sub-micro, and micro) interact with relevant immune cells (primary dendritic cells and macrophages). Particles of all three sizes are readily taken up into both cell types by phagocytosis, but the uptake by macrophages is significantly more prominent than that by dendritic cells. The cells take up particles until they are virtually stuffed, but without direct adverse effect. The uptake increases with time and particle concentration. Thus, we have an ideal model system to follow particles into and inside cells without the side effect of a chemical particle effect, e.g. by degradation or ion release. © 2018 Acta Materialia Inc.
view abstract doi: 10.1016/j.actbio.2018.09.026 2018 • 308 Cold gas spraying of Ti-48Al-2Cr-2Nb intermetallic for jet engine applications
Bakan, E. and Mauer, G. and Sohn, Y.J. and Schwedt, A. and Rackel, M.W. and Riedlberger, F. and Pyczak, F. and Peters, J.O. and Mecklenburg, M. and Gartner, T.M. and Vaßen, R.
Surface and Coatings Technology (2018)The present article describes aspects of the cold gas spray processability of the intermetallic Ti-48Al-2Cr-2Nb (at. %) alloy, which is employed as a structural material in gas turbine engines. The effects of processing parameters, namely, gas pressure, gas temperature, spray distance, as well as the gas atomized feedstock particle size (d50 = 30 and 42 μm, respectively) and phase composition on deposition, were investigated. The results showed that when the highest available gas pressure (40 bar) and temperature (950 °C) were combined with a short spray distance (20 mm), well-adhering coatings could be deposited regardless of the investigated particle size. However, the maximum coating thickness could be achieved was about 30 μm with a deposition efficiency of 1%. Phase composition of the gas atomized feedstock was investigated with HT-XRD and according to the findings, heat treatment of the feedstock under vacuum was carried out. With this treatment, non-equilibrium, disordered α phase of the atomized powder was transformed into an α α2 and γ phase mixture. At the same time, an increase in the hardness and oxygen content of the powder was detected. Swipe test performed with the heat treated powder revealed no improvement in terms of deposition, in fact, the number of adhering particles on the substrate was decreased in comparison with that of the untreated powder. © 2018 Elsevier B.V.
view abstract doi: 10.1016/j.surfcoat.2018.11.092 2018 • 307 Conditions for nucleation and growth in the substrate boundary layer at plasma spray-physical vapor deposition (PS-PVD)
Mauer, G. and Vaßen, R.
Surface and Coatings Technology (2018)Plasma spray-physical vapor deposition (PS-PVD) is a novel coating process based on plasma spraying. In contrast to conventional methods, deposition can come off not only from liquid splats but also from vapor phase. Moreover, there is the suggestion that also nano-sized clusters can be formed by homogeneous nucleation and contribute to deposition. In this work, the conditions for nucleation and growth of such nano-sized particles in the plasma flow around the substrate under PS-PVD conditions were investigated. A boundary layer kinetics model was coupled to an approach for homogeneous nucleation from supersaturated vapors and primary particle growth by condensation as well as secondary particle formation by coagulation. The results confirm the importance of the boundary layer on the substrate. However, since these particles are relatively small, their contribution to coating deposition is limited. Furthermore, microstructure or crystallographic orientations are unlikely to be affected by this cluster deposition. © 2018 Elsevier B.V.
view abstract doi: 10.1016/j.surfcoat.2018.06.086 2018 • 306 Depositing laser-generated nanoparticles on powders for additive manufacturing of oxide dispersed strengthened alloy parts via laser metal deposition
Streubel, R. and Wilms, M.B. and Doñate-Buendía, C. and Weisheit, A. and Barcikowski, S. and Schleifenbaum, J.H. and Gökce, B.
Japanese Journal of Applied Physics 57 (2018)We present a novel route for the adsorption of pulsed laser-dispersed nanoparticles onto metal powders in aqueous solution without using any binders or surfactants. By electrostatic interaction, we deposit Y2O3 nanoparticles onto iron-chromium based powders and obtain a high dispersion of nano-sized particles on the metallic powders. Within the additively manufactured component, we show that the particle spacing of the oxide inclusion can be adjusted by the initial mass fraction of the adsorbed Y2O3 particles on the micropowder. Thus, our procedure constitutes a robust route for additive manufacturing of oxide dispersion-strengthened alloys via oxide nanoparticles supported on steel micropowders. © 2018 The Japan Society of Applied Physics.
view abstract doi: 10.7567/JJAP.57.040310 2018 • 305 Determination of pore size gradients of virus filtration membranes using gold nanoparticles and their relation to fouling with protein containing feed streams
Kosiol, P. and Müller, M.T. and Schneider, B. and Hansmann, B. and Thom, V. and Ulbricht, M.
Journal of Membrane Science 548 598-608 (2018)Virus filtration membranes contribute to the virus safety of biopharmaceutical drugs due to their capability to retain virus particles mainly based on size-exclusion mechanisms. Typical product molecules like monoclonal antibodies with 9–12 nm in hydrodynamic diameter have to be transmitted by >95% while small viruses, e.g. parvoviridae (B19, MVM, PPV) with a diameter of 18–26 nm, have to be retained by at least 99.99%. Therefore, membrane fouling caused by product aggregates, which are similar in size compared to the viruses that have to be retained, is a common observation. Minimal membrane fouling is a requirement for economical processes and is influenced by both the membrane surface chemistry and the membrane structure, particularly with regard to the pore size gradient (PSG). In this work, virus filtration membranes were challenged with gold nanoparticles (GNPs) in order to determine PSGs for a wide range of different commercial and non-commercial parvovirus retentive membranes differing in structure, material and surface chemistry. GNP adsorption to the membrane material was suppressed by the use of an anionic surfactant, allowing to gain insights into size-exclusion properties of the membranes. Membrane performance with regard to fouling was further investigated by determination of protein mass throughputs up-to a defined membrane flux decay using solutions containing intravenous immunoglobulin (IVIG) as model protein. Additionally, the fouling mechanism of IVIG was investigated and confirmed to be caused by trace amounts of species larger than IVIG monomers and dimers, which were already present in the feed. The fouling results are discussed in relationship to the determined PSGs, since the porous support structure of virus filtration membranes can act as a depth pre-filter protecting the separation-active layer from particulate foulants. © 2017 Elsevier B.V.
view abstract doi: 10.1016/j.memsci.2017.11.048 2018 • 304 Ejector-based sampling from low-pressure aerosol reactors
Rosenberger, T. and Münzer, A. and Kiesler, D. and Wiggers, H. and Kruis, F.E.
Journal of Aerosol Science 123 105-115 (2018)Online measurements of nanoparticles are necessary when rapid information about the particle size and mass distribution is needed. Currently, the application of online measurement techniques with commonly used instruments such as SMPS, CPMA and ELPI+ is not possible at low-pressure conditions. In this work, a commercial vacuum ejector is used as a simple tool to transfer nanoparticles from a low-pressure region to atmospheric pressure. The vacuum ejector is investigated for different process pressures between 120 and 170 mbar to measure size-selected aerosols in the range from 10 to 100 nm. It was found that the sampling with the vacuum ejector does not change the particle size. The gas and particle dilution factors as well as the particle losses are determined, so that quantitative measurements of the aerosol size distribution can be obtained. Additionally, the applicability of the vacuum ejector is tested during particle synthesis in a low-pressure microwave plasma reactor with a combination of online instrumentation. The direct transfer of the aerosol to atmospheric pressure allows real-time measurements. The primary particle size, mass mobility exponent and effective density are calculated exemplary based on parallel online ELPI+, SMPS and CPMA measurements and are compared to offline TEM analysis. © 2018 Elsevier Ltd
view abstract doi: 10.1016/j.jaerosci.2018.06.003 2018 • 303 Experimental analysis of the flow conditions in spiral jet mills via non-invasive optical methods
Luczak, B. and Müller, R. and Ulbricht, M. and Schultz, H.J.
Powder Technology 325 161-166 (2018)Although most of the parameters affecting spiral jet milling have already been studied, there are no investigations of several parameters and their effects on the flow conditions over the entire cross-section inside the spiral jet mill via non-invasive methods. In order to vary several geometrical and operative parameters and to determine the flow conditions inside the jet mill, a new type of experimental spiral jet mill apparatus was designed and constructed. It has an almost entire optical accessibility and its highly modular construction enables a very convenient variation of the geometric parameters. This paper describes the new type of mill apparatus and preliminary experimental results concerning the flow conditions inside the spiral jet mill as well as grinding effects under different conditions on particle size distributions of barium sulphate micro particles. © 2017 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2017.10.048 2018 • 302 Fully automated primary particle size analysis of agglomerates on transmission electron microscopy images via artificial neural networks
Frei, M. and Kruis, F.E.
Powder Technology 332 120-130 (2018)There is a high demand for fully automated methods for the analysis of primary particle size distributions of agglomerates on transmission electron microscopy images. Therefore, a novel method, based on the utilization of artificial neural networks, was proposed, implemented and validated. The training of the artificial neural networks requires large quantities (up to several hundreds of thousands) of transmission electron microscopy images of agglomerates consisting of primary particles with known sizes. Since the manual evaluation of such large amounts of transmission electron microscopy images is not feasible, a synthesis of lifelike transmission electron microscopy images as training data was implemented. The proposed method can compete with state-of-the-art automated imaging particle size methods like the Hough transformation, ultimate erosion and watershed transformation and is in some cases even able to outperform these methods. It is however still outperformed by the manual analysis. © 2018 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2018.03.032 2018 • 301 In situ atomic-scale observation of oxidation and decomposition processes in nanocrystalline alloys
Guo, J. and Haberfehlner, G. and Rosalie, J. and Li, L. and Duarte, M.J. and Kothleitner, G. and Dehm, G. and He, Y. and Pippan, R. and Zhang, Z.
Nature Communications 9 (2018)Oxygen contamination is a problem which inevitably occurs during severe plastic deformation of metallic powders by exposure to air. Although this contamination can change the morphology and properties of the consolidated materials, there is a lack of detailed information about the behavior of oxygen in nanocrystalline alloys. In this study, aberration-corrected high-resolution transmission electron microscopy and associated techniques are used to investigate the behavior of oxygen during in situ heating of highly strained Cu-Fe alloys. Contrary to expectations, oxide formation occurs prior to the decomposition of the metastable Cu-Fe solid solution. This oxide formation commences at relatively low temperatures, generating nanosized clusters of firstly CuO and later Fe2O3. The orientation relationship between these clusters and the matrix differs from that observed in conventional steels. These findings provide a direct observation of oxide formation in single-phase Cu-Fe composites and offer a pathway for the design of nanocrystalline materials strengthened by oxide dispersions. © 2018 The Author(s).
view abstract doi: 10.1038/s41467-018-03288-8 2018 • 300 Influence of controlled functionalization of mesoporous silica nanoparticles as tailored fillers for thin-film nanocomposite membranes on desalination performance
Abdelsamad, A.M.A. and Khalil, A.S.G. and Ulbricht, M.
Journal of Membrane Science 563 149-161 (2018)Thin film nanocomposite (TFN) membranes comprising of controlled functionalized mesoporous silica nanoparticles (MSN) blended in the polyamide (PA) barrier layer were prepared via interfacial polymerization of m-phenylenediamine and trimesoyl chloride on a porous polyethersulfone support membrane. MSN were synthesized by sol-gel process and then functionalized with octadecyltrichlorosilane (OTS) using post-grafting method. The nitrogen adsorption measurements demonstrated that the hydrophobic alkyl chains of OTS can be grafted onto the internal pores of MSN or just be located on the external particle surface, depending on the functionalization procedure and the OTS concentration. The functionalized nanoparticles with a diameter of about 80 nm were thereafter easily dispersed in the organic phase during the interfacial polymerization. Evaluation of membranes’ performance was based on water and ethanol permeability measurements, in addition to salt rejection from aqueous solutions. The results indicated that the functionalization of the external surface of MSN only, without extension to the interior pores surface, significantly increased both water and ethanol permeabilities. Contrarily, the surface modification of the MSN internal pores only increased the permeability of ethanol and reduced the water permeability, mainly due to the hydrophobicity of OTS. The influence of nanoparticles loading, as well as the concentration of OTS and thus the extent of MSN functionalization on the separation performance of TFN membranes were also investigated. TFN membranes prepared using the optimized MSN functionalization and loading yielded up to 63% higher water permeability compared to the reference thin film composite membrane without sacrificing the membrane selectivity. This work clearly emphasizes the direct relationship between the internal pores of MSN as functional nanofiller in the PA barrier layer and increasing or decreasing the water permeability of resulting TFN membranes. © 2018 Elsevier B.V.
view abstract doi: 10.1016/j.memsci.2018.05.043 2018 • 299 Influence of Feedstock Powder Modification by Heat Treatments on the Properties of APS-Sprayed Al2O3-40% TiO2 Coatings
Berger, L.-M. and Sempf, K. and Sohn, Y.J. and Vaßen, R.
Journal of Thermal Spray Technology 27 654-666 (2018)The formation and decomposition of aluminum titanate (Al2TiO5, tialite) in feedstock powders and coatings of the binary Al2O3-TiO2 system are so far poorly understood. A commercial fused and crushed Al2O3-40%TiO2 powder was selected as the feedstock for the experimental series presented in this paper, as the composition is close to that of Al2TiO5. Part of that powder was heat-treated in air at 1150 and 1500 °C in order to modify the phase composition, while not influencing the particle size distribution and processability. The powders were analyzed by thermal analysis, XRD and FESEM including EDS of metallographically prepared cross sections. Only a maximum content of about 45 wt.% Al2TiO5 was possible to obtain with the heat treatment at 1500 °C due to inhomogeneous distribution of Al and Ti in the original powder. Coatings were prepared by plasma spraying using a TriplexPro-210 (Oerlikon Metco) with Ar-H2 and Ar-He plasma gas mixtures at plasma power levels of 41 and 48 kW. Coatings were studied by XRD, SEM including EDS linescans of metallographically prepared cross sections, and microhardness HV1. With the exception of the powder heat-treated at 1500 °C an Al2TiO5-Ti3O5 (tialite–anosovite) solid solution Al2−xTi1+xO5 instead of Al2TiO5 existed in the initial powder and the coatings. © 2018, ASM International.
view abstract doi: 10.1007/s11666-018-0716-0 2018 • 298 Kinetic study of gold nanoparticles synthesized in the presence of chitosan and citric acid
Simeonova, S. and Georgiev, P. and Exner, K.S. and Mihaylov, L. and Nihtianova, D. and Koynov, K. and Balashev, K.
Colloids and Surfaces A: Physicochemical and Engineering Aspects 557 106-115 (2018)In this work colloidal gold nanoparticles (GNPs) are prepared using a citrate-reduction route, in which citric acid serves as reductive agent for the gold precursor HAuCl4. We demonstrate that a temperature variation on the one hand enables to tune the reaction rate of GNP formation and on the other hand allows modifying the morphology of the resulting metal nanoparticles. The use of chitosan, a biocompatible and biodegradable polymer with a multitude of functional amino and hydroxyl groups, facilitates the simultaneous synthesis and surface modification of GNPs in one pot. The resulting GNPs, which are stabilized by a network of chitosan and ß-ketoglutaric acid units, are characterized by UV–vis spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM) as well as fluorescence correlation spectroscopy (FCS) and reveal an average diameter of about 10 nm at the end of the synthesis. The kinetics of GNP formation is studied by calculating activation parameters based on UV–vis and AFM data such as the apparent activation energy, entropy and free energy applying the concept of the Finke-Watzky model and harmonic transition state theory. © 2018 Elsevier B.V.
view abstract doi: 10.1016/j.colsurfa.2018.02.045 2018 • 297 Laser Fragmentation of Colloidal Gold Nanoparticles with High-Intensity Nanosecond Pulses is Driven by a Single-Step Fragmentation Mechanism with a Defined Educt Particle-Size Threshold
Ziefuß, A.R. and Reichenberger, S. and Rehbock, C. and Chakraborty, I. and Gharib, M. and Parak, W.J. and Barcikowski, S.
Journal of Physical Chemistry C 122 22125-22136 (2018)Laser-inducd fragmentation is a promising tool for controlling the particle size of ligand-free colloidal nanoparticles and to synthesize ligand-free gold nanoclusters. However, because the underlying mechanisms are not fully understood, increasing the yield of this process remains challenging. In this work, we examine the pulsed laser fragmentation of gold nanoparticles in liquid under statistical single-pulse conditions with high-fluence nanosecond pulses and correlate them with the educt particle size, number of pulses, and laser fluence. We conclusively prove that the fragmentation process of gold nanoparticles is a one-pulse and one-step event, which yields monomodal particles of 10 nm down to 2.8 +/- 0.1 nm when exceeding a pulse peak power of 1.6 × 1012 W/m2 and when all educt particles are larger than 13.4 nm. This size threshold for quantitative fragmentation fits well with the size limit of 13.1 nm calculated with respect to the evaporation-heat-energy balance. Furthermore, we found strong evidence that the number of irradiation cycles, varied within the regime of one to four laser pulses/colloid volume, can be used to tune the surface chemistry and surface charge of the resulting nanoparticles in an aqueous medium. © 2018 American Chemical Society.
view abstract doi: 10.1021/acs.jpcc.8b04374 2018 • 296 On-surface nickel porphyrin mimics the reactive center of an enzyme cofactor
Zamborlini, G. and Jugovac, M. and Cossaro, A. and Verdini, A. and Floreano, L. and Lüftner, D. and Puschnig, P. and Feyer, V. and Schneider, C.M.
Chemical Communications 54 13423-13426 (2018)Metal-containing enzyme cofactors achieve their unusual reactivity by stabilizing uncommon metal oxidation states with structurally complex ligands. In particular, the specific cofactor promoting both methanogenesis and anaerobic methane oxidation is a porphyrinoid chelated to a nickel(i) atom via a multi-step biosynthetic path, where nickel reduction is achieved through extensive molecular hydrogenation. Here, we demonstrate an alternative route to porphyrin reduction by charge transfer from a selected copper substrate to commercially available 5,10,15,20-tetraphenyl-porphyrin nickel(ii). X-ray absorption measurements at the Ni L3-edge unequivocally show that NiTPP species adsorbed on Cu(100) are stabilized in the highly reactive Ni(i) oxidation state by electron transfer to the molecular orbitals. Our approach highlights how some fundamental properties of synthetically inaccessible biological cofactors may be reproduced by hybridization of simple metalloporphyrins with metal surfaces, with implications towards novel approaches to heterogenous catalysis. © 2018 The Royal Society of Chemistry.
view abstract doi: 10.1039/c8cc06739b 2018 • 295 Parameter free quantitative analysis of atom probe data by correlation functions: Application to the precipitation in Al-Zn-Mg-Cu
Zhao, H. and Gault, B. and Ponge, D. and Raabe, D. and De Geuser, F.
Scripta Materialia 154 106-110 (2018)Atom probe tomography enables precise quantification of the composition of second phase particles from their early stages, leading to improved understanding of the thermodynamic and kinetic mechanisms of phase formation and quantify structure-property relationships. Here we demonstrate how approaches developed for small-angle scattering can be adapted to atom probe tomography. By exploiting nearest-neighbor distributions and radial distribution function, we introduce a parameter free methodology to efficiently extract information such as particle size, composition, volume fraction, number density and inter-particle distance. We demonstrate the strength of this approach in the analysis of a precipitation-hardened model Al-Zn-Mg-Cu high-strength lightweight alloy. © 2018 Elsevier Ltd
view abstract doi: 10.1016/j.scriptamat.2018.05.024 2018 • 294 Preparation of spray dried submicron particles: Part A – Particle generation by aerosol conditioning
Strob, R. and Dobrowolski, A. and Schaldach, G. and Walzel, P. and Thommes, M.
International Journal of Pharmaceutics 548 423-430 (2018)The preparation of submicron-sized particles is relevant in chemical, food and pharmaceutical applications. In pharmaceutics, spray dried submicron-sized particles (0.1–1 µm) can increase the dissolution rate as well as the solubility of poorly water-soluble drugs. Since the particle size during spray drying is mainly influenced by the droplet size, the preparation of uniform droplets smaller than 3 µm is of particular interest. In this work, a two-fluid nozzle was combined with a cyclone droplet separator. Droplets larger than the cut-off size were separated with a cyclone droplet separator and returned to the liquid feed. The aerosol at the outlet of the droplet separator was subsequently dried. The drop size of the conditioned aerosol was small, d50,3=2 µm, and independent of the liquid-to-gas mass flow ratio and the viscosity of the liquid feed. Thus it only depended on the characteristics of the separator. Finally, the dried particles were spherical in shape and in the submicron-sized range. © 2018 Elsevier B.V.
view abstract doi: 10.1016/j.ijpharm.2018.06.067 2018 • 293 Preparation of spray dried submicron particles: Part B – Particle recovery by electrostatic precipitation
Dobrowolski, A. and Strob, R. and Nietfeld, J. and Pieloth, D. and Wiggers, H. and Thommes, M.
International Journal of Pharmaceutics 548 237-243 (2018)The low bioavailability of poorly water-soluble drugs is currently one of the major focuses of pharmaceutical research. One strategy currently being investigated to overcome this limitation is to decrease the particle size of the active pharmaceutical ingredients (API). An innovative process for this is spray drying with spray conditioning, which can produce submicron particles. One challenge resulting from this process is the recovery of these dispersed particles from a gas flow. Electrostatic precipitation is a common technique for air purification purposes, but an adapted electrostatic precipitator (ESP) design is necessary to achieve high collection efficiencies. The ESP design in this work uses the precipitation method of Penney filters which separates charging and collection into two stages. The ESP dimensions depend on various assumptions and simplifications. Several experiments were conducted to assess the performance of the ESP and characterize its behaviour in long-term tests. The crucial parameters in the charging process are the residence time as well as the operating voltage. These constraints were examined to enhance the collection efficiency. Based on these tests it was possible to determine a suitable charging length as well as the dimensions of the collection stage. In conclusion, an ESP customized for collecting particles in the range of 0.1–1 µm was designed, built and tested, and collection efficiencies higher than 99% were achieved for submicron particle size distributions. For a robust process continuous cleaning of the charging stage is necessary. © 2018 Elsevier B.V.
view abstract doi: 10.1016/j.ijpharm.2018.06.069 2018 • 292 Primary particle diameter differentiation and bimodality identification by five analytical methods using gold nanoparticle size distributions synthesized by pulsed laser ablation in liquids
Letzel, A. and Gökce, B. and Menzel, A. and Plech, A. and Barcikowski, S.
Applied Surface Science 435 743-751 (2018)For a known material, the size distribution of a nanoparticle colloid is a crucial parameter that defines its properties. However, measured size distributions are not easy to interpret as one has to consider weighting (e.g. by light absorption, scattering intensity, volume, surface, number) and the way size information was gained. The radius of a suspended nanoparticle can be given as e.g. sphere equivalent, hydrodynamic, Feret or radius of gyration. In this study, gold nanoparticles in water are synthesized by pulsed-laser ablation (LAL) and fragmentation (LFL) in liquids and characterized by various techniques (scanning transmission electron microscopy (STEM), small-angle X-ray scattering (SAXS), analytical disc centrifugation (ADC), dynamic light scattering (DLS) and UV–vis spectroscopy with Mie-Gans Theory) to study the comparability of different analytical techniques and determine the method that is preferable for a given task related to laser-generated nanoparticles. In particular, laser-generated colloids are known to be bimodal and/or polydisperse, but bimodality is sometimes not analytically resolved in literature. In addition, frequently reported small size shifts of the primary particle mode around 10 nm needs evaluation of its statistical significance related to the analytical method. Closely related to earlier studies on SAXS, different colloids in defined proportions are mixed and their size as a function of the nominal mixing ratio is analyzed. It is found that the derived particle size is independent of the nominal mixing ratio if the colloid size fractions do not overlap considerably. Conversely, the obtained size for colloids with overlapping size fractions strongly depends on the nominal mixing ratio since most methods cannot distinguish between such fractions. Overall, SAXS and ADC are very accurate methods for particle size analysis. Further, the ability of different methods to determine the nominal mixing ratio of sizes fractions is studied experimentally. © 2017 Elsevier B.V.
view abstract doi: 10.1016/j.apsusc.2017.11.130 2018 • 291 Quantitative evaluation of nanoparticle classification by size-exclusion chromatography
Süß, S. and Metzger, C. and Damm, C. and Segets, D. and Peukert, W.
Powder Technology 339 264-272 (2018)Although few attempts for classification of nanoparticles (NPs) in labscale do exist, the transfer to industrial applications is still challenging. One promising separation method, which is already established for biological molecules, is chromatography. Herein, we study the classification of differently sized gold NPs (AuNPs) by size-exclusion chromatography (SEC). First, we investigated the interactions of AuNPs with potential stationary phases in order to identify a suitable material for the chromatographic process where irreversible NP adhesion is excluded. Then, we demonstrate the high reproducibility of our SEC experiments by multiple sample injections that lead to constant peak areas. In particular, we show the size-dependent elution behavior of AuNP mixtures resulting in bimodal elution peaks, where size separation was confirmed by inline measured UV/Vis spectra. Finally, NP classification results by using a fraction collector are characterized by retention time, mass balances and size-dependent separation efficiencies. The adjustment of the particle size distributions (PSDs) is demonstrated by changing the switching time of the fraction collector. Our study evidences the high potential of SEC for preparative and continuous separation of NPs. © 2018 The Authors
view abstract doi: 10.1016/j.powtec.2018.08.008 2018 • 290 Retention mechanisms of 1.7 nm ZnS quantum dots and sub-20 nm Au nanoparticles in ultrafiltration membranes
Lee, H. and Segets, D. and Süß, S. and Peukert, W. and Chen, S.-C. and Pui, D.Y.H.
Journal of Membrane Science 567 58-67 (2018)Membrane processes are considered to be a very effective and promising method for drinking water and wastewater treatments. However, particle removal mechanisms have not been fully elucidated due to complex surface interactions between colloids and membranes, especially for very small colloidal particles. In this study, a series of systematic filtration tests for eight different types of membrane filters, having nominal pore sizes from 0.005 to 0.1 µm, against 1.7 nm ZnS quantum dots (QDs) and 5, 10 and 20 nm Au nanoparticles (NPs) was performed to understand their retention mechanisms, including rejection in front of the filter surface and adsorption inside the filter. By comparing rejection, adsorption and recovery, it was found that the predominant retention mechanisms for retaining small NPs varied from filter to filter. For instance, electrostatic repulsion played a significant role for the rejection of NPs, i.e. impeding them entering the membrane pores in most membranes. In comparison, the Nylon membrane had a significant adsorption retention ability for Au NPs due to electrostatic attraction. Besides, it was found that filtration flow rate, or flux, was also an important parameter for the final retention because the enhanced hydrodynamic drag could trigger the detachment of deposited NPs or press NPs flowing through the superficial entrance leading to penetration. Tests of 10 nm Au NP retention using five different membranes with the same nominal pore size of 0.1 µm showed large variation of NP retention efficiencies demonstrating that pore size should not be used as the only criterion for rating filter performance, especially for small NPs. Our results provide not only detailed insights into the retention mechanisms of various membranes but also suggestions on how to select membrane filters for different filtration purposes. © 2018 Elsevier B.V.
view abstract doi: 10.1016/j.memsci.2018.09.033 2018 • 289 Scaling-up metal nanoparticle production by transferred arc discharge
Stein, M. and Kruis, F.E.
Advanced Powder Technology 29 3138-3144 (2018)The number of applications and products containing metal nanomaterials has significantly increased over the past years. In order to address the upcoming demand for metal nanoparticles, new scale-up strategies are required. The scale-up of nanoparticle synthesis, especially for metals, is however very challenging. This study reports about a production facility with a new scale-up approach for pure metal nanoparticles. The scale-up approach is the parallelization of multiple transferred arcs in one reactor, which were previously individually optimized. Furthermore, a novel filtration and bagging system is introduced, which is designed to handle pyrophoric metal nanoparticles. It is shown that the production rate of the process scales linearly with the number of transferred arcs, while the particle size stays on the nanoscale. © 2018 The Society of Powder Technology Japan
view abstract doi: 10.1016/j.apt.2018.08.016 2018 • 288 The influence of hydrogen and methane on the growth of carbon particles during acetylene pyrolysis in a burnt-gas flow reactor
Peukert, S. and Sallom, A. and Emelianov, A. and Endres, T. and Fikri, M. and Böhm, H. and Jander, H. and Eremin, A. and Schulz, C.
Proceedings of the Combustion Institute (2018)The growth of carbon particles was studied in heated flows of a burnt-gas flow reactor containing mixtures of N2/C2H2, and N2/C2H2 with addition of H2 or CH4 surrounded by a rich C2H4/air flame. Soot particle sizes and volume fractions were measured by laser-induced incandescence (LII) between 50 and 130 mm above the nozzle exit. The measurements indicate a soot-inhibiting effect of adding H2 to the C2H2/N2 flow on both, particle sizes and soot volume fractions. The effect of CH4 addition to the C2H2/N2 flows was ambivalent, depending on the methane-to-acetylene ratio. At gas mixtures with N2:CH4:C2H2 = 0.42:0.35:0.23 and 0.39:0.32:0.29 by volume at fixed total flow rates, the measured soot volume fractions were substantially increased in presence of CH4, while the mean diameters of the particles were slightly decreased. Gas temperatures were measured by a generalized line-reversal method with Abel transformation. Temperatures of the surrounding C2H4/air flame were around 1600 K, and temperatures of the inner flows, where soot formation was measured, were between 1550 and 1630 K. Plug-flow reactor calculations provided a qualitative understanding of the influence of CH4 on the soot particle growth. © 2018.
view abstract doi: 10.1016/j.proci.2018.05.049 2018 • 287 Transient DEM-CFD simulation of solid and fluid flow in a three dimensional blast furnace model
Bambauer, F. and Wirtz, S. and Scherer, V. and Bartusch, H.
Powder Technology 334 53-64 (2018)A numerical investigation of gas and solid flow as well as the liquid accumulation in a scaled Blast Furnace (BF) model was carried out using the discrete element method (DEM) coupled with computational fluid dynamics (CFD). This three dimensional simulation considers the interaction of the solid flow of a layered burden column with the counter flowing process gas. The influence of the cohesive zone is modeled by a material dependent permeability, the molten iron and the slag are considered as one additional liquid phase in the hearth. The method used is compared with a two dimensional numerical slot model presented in former publications by Zhou et al. and then applied to a different three dimensional setup. The comparison of the models exhibits considerable differences concerning the general multiphase flow behaviour. Moreover, it is shown that three dimensional models are required to correctly resolve the actual spatial flow structure and its influence on the shape of the coke free region in the hearth. Finally, the three dimensional model is used to show the influence of the liquid discharge on the stress distribution along the walls. © 2017 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2018.04.062 2018 • 286 Ultrafine and fine particle number and surface area concentrations and daily cause-specific mortality in the Ruhr area, Germany, 2009–2014
Hennig, F. and Quass, U. and Hellack, B. and Küpper, M. and Kuhlbusch, T.A.J. and Stafoggia, M. and Hoffmann, B.
Environmental Health Perspectives 126 (2018)BACKGROUND: Although epidemiologic studies have shown associations between particle mass and daily mortality, evidence on other particle metrics is weak. OBJECTIVES: We investigated associations of size-specific particle number concentration (PNC) and lung-deposited particle surface area concentration (PSC) with cause-specific daily mortality in contrast to PM10. METHODS: We used time-series data (March 2009–December 2014) on daily natural, cardiovascular, and respiratory mortality (NM, CVM, RM) of three adjacent cities in the Ruhr Area, Germany. Size-specific PNC (electric mobility diameter of 13.3–750 nm), PSC, and PM10 were measured at an urban background monitoring site. In single- and multipollutant Poisson regression models, we estimated percentage change (95% confidence interval) [% (95% CI)] in mortality per interquartile range (IQR) in exposure at single-day (0–7) and aggregated lags (0–1, 2–3, 4–7), accounting for time trend, temperature, humidity, day of week, holidays, period of seasonal population decrease, and influenza. RESULTS: PNC100–750 and PSC were highly correlated and had similar immediate (lag0–1) and delayed (lag4–7) associations with NM and CVM, for example, 1.12% (95% CI: 0.09, 2.33) and 1.56% (95% CI: 0.22, 2.92) higher NM with IQR increases in PNC100–750 at lag0–1 and lag4–7, respectfully, which were slightly stronger then associations with IQR increases in PM10. Positive associations between PNC and NM were strongest for accumulation mode particles (PNC 100–500 nm), and for larger UFPs (PNC 50–100 nm). Associations between NM and PNC<100 changed little after adjustment for O3 or PM10, but were more sensitive to adjustment for NO2. CONCLUSION: Size-specific PNC (50–500 nm) and lung-deposited PSC were associated with natural and cardiovascular mortality in the Ruhr Area. Although associations were similar to those estimated for an IQR increase in PM10, particle number size distributions can be linked to emission sources, and thus may be more informative for potential public health interventions. Moreover, PSC could be used as an alternative metric that integrates particle size distribution as well as deposition efficiency. © 2018, Public Health Services, US Dept of Health and Human Services. All rights reserved.
view abstract doi: 10.1289/EHP2054 2018 • 285 Vacuum plasma spraying of functionally graded tungsten/EUROFER97 coatings for fusion applications
Vaßen, R. and Rauwald, K.-H. and Guillon, O. and Aktaa, J. and Weber, T. and Back, H.C. and Qu, D. and Gibmeier, J.
Fusion Engineering and Design 133 148-156 (2018)As structural materials for future fusion power plants, reduced activation ferritic martensitic steels as EUROFER97 can be used. Unfortunately, the interaction of the plasma with the steel would result in a limited lifetime, so protective layers are investigated. An excellent protective material is tungsten, as it shows unique properties with respect to low sputtering, high melting points and low activation. However, the mismatch of thermo-physical properties between tungsten and EUROFER97 can lead to large stress levels and even failure. A possible way to overcome this problem is the use of functionally graded material (FGM). The paper will describe the manufacture of these FGMs by vacuum plasma spraying and their characterization. First of all, two different feeding lines have been used to produce the coatings. A major problem lies in different melting points of tungsten and steel. So the particle size distribution has to be adjusted to achieve sufficient melting of both materials during the spray process. In a second step, the feeding rates were optimized to obtain the wanted amount of tungsten and steel phases in the graded structures. In a thermal spray process, the gradient cannot be made continuously, however it has to be applied in a step-wise manner. In this investigation, samples with 3 and 5 different concentrations (excluding the pure steel and tungsten part) have been produced. The microstructures of these layers have been investigated. In addition, hardness was measured and the residual stress state was determined by the hole drilling method. © 2018
view abstract doi: 10.1016/j.fusengdes.2018.06.006 2017 • 284 2D analysis of polydisperse core-shell nanoparticles using analytical ultracentrifugation
Walter, J. and Gorbet, G. and Akdas, T. and Segets, D. and Demeler, B. and Peukert, W.
Analyst 142 206-217 (2017)Accurate knowledge of the size, density and composition of nanoparticles (NPs) is of major importance for their applications. In this work the hydrodynamic characterization of polydisperse core-shell NPs by means of analytical ultracentrifugation (AUC) is addressed. AUC is one of the most accurate techniques for the characterization of NPs in the liquid phase because it can resolve particle size distributions (PSDs) with unrivaled resolution and detail. Small NPs have to be considered as core-shell systems when dispersed in a liquid since a solvation layer and a stabilizer shell will significantly contribute to the particle's hydrodynamic diameter and effective density. AUC measures the sedimentation and diffusion transport of the analytes, which are affected by the core-shell compositional properties. This work demonstrates that polydisperse and thus widely distributed NPs pose significant challenges for current state-of-the-art data evaluation methods. The existing methods either have insufficient resolution or do not correctly reproduce the core-shell properties. First, we investigate the performance of different data evaluation models by means of simulated data. Then, we propose a new methodology to address the core-shell properties of NPs. This method is based on the parametrically constrained spectrum analysis and offers complete access to the size and effective density of polydisperse NPs. Our study is complemented using experimental data derived for ZnO and CuInS2 NPs, which do not have a monodisperse PSD. For the first time, the size and effective density of such structures could be resolved with high resolution by means of a two-dimensional AUC analysis approach. © 2017 The Royal Society of Chemistry.
view abstract doi: 10.1039/c6an02236g 2017 • 283 3D-DEM-CFD simulation of heat and mass transfer, gas combustion and calcination in an intermittent operating lime shaft kiln
Krause, B. and Liedmann, B. and Wiese, J. and Bucher, P. and Wirtz, S. and Piringer, H. and Scherer, V.
International Journal of Thermal Sciences 117 121-135 (2017)This work presents DEM-CFD simulations of the transient processes occurring in an industrial scale PFR-kiln. DEM allows the numerical simulation of the moving and reacting limestone bed in the kiln and is coupled with a 3-dimensional CFD simulation describing the interstitial gas phase. A PFR-kiln consists of two vertical shafts and a connecting crossover channel. The two shafts periodically switch their function at regular intervals of about 15 min. While one shaft calcines the product in parallel flow with gas temperatures above 900 °C, the other preheats the stones in counter flow. The model has been applied to an industrial PFR-kiln of 18 m height. A realistic particle size distribution of the limestone with particles ranging from 50 to 90 mm has been set. Methane combustion provides the heat for calcination and is simulated by a two-step mechanism. Simulation results show a nearly uniform temperature distribution in the calcination zone but significant inner particle temperature gradients. The calcination degree depends on the particle location within the kiln and decreases towards the outer kiln walls. Measured and simulated temperatures are compared. Maximum temperature values as well as its characteristic oscillation induced by the periodic kiln operation could be reproduced by the simulation, especially keeping in mind the difficulties of thermocouple measurements under the harsh conditions in industrial reality. © 2017 Elsevier Masson SAS
view abstract doi: 10.1016/j.ijthermalsci.2017.03.017 2017 • 282 A single intraperitoneal injection of bovine fetuin-A attenuates bone resorption in a murine calvarial model of particle-induced osteolysis
Jablonski, H. and Polan, C. and Wedemeyer, C. and Hilken, G. and Schlepper, R. and Bachmann, H.S. and Grabellus, F. and Dudda, M. and Jäger, M. and Kauther, M.D.
Bone 105 262-268 (2017)Particle-induced osteolysis, which by definition is an aseptic inflammatory reaction to implant-derived wear debris eventually leading to local bone destruction, remains the major reason for long-term failure of orthopedic endoprostheses. Fetuin-A, a 66 kDa glycoprotein with diverse functions, is found to be enriched in bone. Besides being an important inhibitor of ectopic calcification, it has been described to influence the production of mediators of inflammation. Furthermore, a regulatory role in bone metabolism has been assigned. In the present study, the influence of a single dose of bovine fetuin-A, intraperitoneally injected in mice subjected to particle-induced osteolysis of the calvaria, was analyzed. Twenty-eight male C57BL/6 mice, twelve weeks of age, were randomly divided into four groups. Groups 2 and 4 were subjected to ultra-high molecular weight polyethylene (UHMWPE) particles placed on their calvariae while groups 1 and 3 were sham-operated. Furthermore, groups 3 and 4 received a single intraperitoneal injection of 20 mg bovine fetuin-A while groups 1 and 2 were treated with physiologic saline. After 14 days calvarial bone was qualitatively and quantitatively assessed using microcomputed tomography (μCT) and histomorphometrical approaches. Application of fetuin-A led to a reduction of particle-induced osteolysis in terms of visible osteolytic lesions and eroded bone surface. The reduction of bone thickness and bone volume, as elicited by UHMWPE, was alleviated by fetuin-A. In conclusion, fetuin-A was found to exert an anti-resorptive effect on particle-induced osteolysis in-vivo. Thus, fetuin-A could play a potentially osteoprotective role in the treatment of bone metabolic disorders. © 2017 Elsevier Inc.
view abstract doi: 10.1016/j.bone.2017.09.006 2017 • 281 A time-driven constant-number Monte Carlo method for the GPU-simulation of particle breakage based on weighted simulation particles
Kotalczyk, G. and Devi, J. and Kruis, F.E.
Powder Technology 317 417-429 (2017)Monte Carlo (MC) simulations based on weighted particles offer novel and more precise techniques for the solution of the population balance equation for particulate systems. A recent constant-number approach named stochastic weighted algorithm (SWA) (Lee et al. (2015), J. Comput. Phys. (303) 1–18) has been developed, which renders the breakage of a simulation particle by an alteration of its properties, without the creation of novel simulation particles. The theoretic justification of the general formulation for all possible SWAs is limited to binary breakage kernels. We present a novel approach for the derivation of the properties of the MC particles representing fragments, which is applicable for all sorts of breakage kernels. This general scheme encompasses the already introduced SWA schemes, especially a number-based (SWA1, named NBS in this paper) and volume-based (SWA2, named VBS in this paper) breakage scheme, and it makes novel formulations possible: the low volume scheme (LVS), which renders preferably lower fragment sizes, and the combination of LVS with the NBS (LVS-NBS) or VBS (LVS-VBS). The implementation of these breakage schemes in the context of a GPU-based time-driven method is presented and the gained results are validated by comparison with results of the analytic solutions of a homogeneous binary breakage kernel. It is found, that the SWA methods (NBS and VBS) are only able to render large particle sizes, and that LVS, NBS-LVS and VBS-LVS are able to render the whole spectrum of particle sizes. Smaller noise levels are found for VBS and specific VBS-LVS schemes, making both more suitable for prolonged simulations than the other presented methods. © 2017 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2017.05.002 2017 • 280 Automated synthesis of quantum dot nanocrystals by hot injection: Mixing induced self-focusing
Salaheldin, A.M. and Walter, J. and Herre, P. and Levchuk, I. and Jabbari, Y. and Kolle, J.M. and Brabec, C.J. and Peukert, W. and Segets, D.
Chemical Engineering Journal 320 232-243 (2017)The hot injection technique for the synthesis of quantum dots (QDs) is a well-established and widely used method in the lab. However, scale-up rules do not exist. One reason is that in particular the role of process parameters like mixing on particle formation is largely unknown, as systematic examination of the latter is impossible for the laborious and complex manual synthesis. Herein we studied the mixing induced self-focusing of particle size distributions (PSDs) of CdSe QDs using automation in combination with a defined stirrer geometry. Basis for our study is a platform that allows parallelization with inline temperature monitoring, defined injection rate, accurate sampling times as well as controlled stirring. Reproducibility in terms of optical product properties was analyzed by absorption and emission whereas reproducibility in terms of the PSD was verified by deconvolution of UV/Vis absorbance spectra and especially by analytical ultracentrifugation (AUC) complemented by transmission electron microscopy (TEM). In line with previous results, AUC confirmed that even QDs made by hot injection in an automated setup are polydisperse with multimodal size distributions. Finally, reproducibility in combination with early stage sampling and controlled mixing allowed us for the first time to analyze the influence of stirring on focusing and defocusing of PSDs, that has been expressed in terms of the evolution of the relative standard deviation (RSD). Our work paves the way to gain in-depth understanding of often forgotten process-structure relationships of colloidal nanoparticles which eventually is a first step in the direction of the development of scalable synthesis and reliable application of high-quality QDs in technical applications. © 2017 Elsevier B.V.
view abstract doi: 10.1016/j.cej.2017.02.154 2017 • 279 Boronic Acid Functionalized Photosensitizers: A Strategy To Target the Surface of Bacteria and Implement Active Agents in Polymer Coatings
Galstyan, A. and Schiller, R. and Dobrindt, U.
Angewandte Chemie - International Edition 56 10362-10366 (2017)Advanced methods for preventing and controlling hospital-acquired infections via eradication of free-floating bacteria and bacterial biofilms are of great interest. In this regard, the attractiveness of unconventional treatment modalities such as antimicrobial photodynamic therapy (aPDT) continues to grow. This study investigated a new and innovative strategy for targeting polysaccharides found on the bacterial cell envelope and the biofilm matrix using the boronic acid functionalized and highly effective photosensitizer (PS) silicon(IV) phthalocyanine. This strategy has been found to be successful in treating planktonic cultures and biofilms of Gram-negative E. coli. An additional advantage of boronic acid functionality is a possibility to anchor the tailor made PS to poly(vinyl alcohol) and to fabricate a self-disinfecting coating. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract doi: 10.1002/anie.201703398 2017 • 278 Changes within the stabilizing layer of ZnO nanoparticles upon washing
Schindler, T. and Schmutzler, T. and Schmiele, M. and Lin, W. and Segets, D. and Peukert, W. and Appavou, M.-S. and Kriele, A. and Gilles, R. and Unruh, T.
Journal of Colloid and Interface Science 504 356-362 (2017)ZnO nanoparticles (NPs) are highly relevant for various industrial applications, however, after synthesis of the NPs residual chemicals need to be removed from the colloidal raw product by washing, as they may influence the performance of the final device. In the present study we focus on the effect of washing by antisolvent flocculation with subsequent redispersion of the NPs on the stabilizing acetate shell. Purification of the ZnO nanoparticles is reported to be optimal with respect to zeta potential that has a maximum after one washing cycle. In this work, we will shed light on this observation using small angle X-ray and neutron scattering (SAXS, SANS) by demonstrating that after the first washing cycle the content of acetate in the ligand shell around the ZnO NPs increases. In detail, it was observed that the diffuse acetate shell shrinks to the size of a monolayer upon washing but the acetate content of this monolayer is higher than within the diffuse shell of the particles of the native dispersion. A second washing cycle reduces the acetate concentration within the stabilizing shell and the stability of the dispersion drops accordingly. After another (third) washing cycle strong agglomeration was observed for all investigated samples. © 2017 Elsevier Inc.
view abstract doi: 10.1016/j.jcis.2017.05.059 2017 • 277 Characterization of recycled TiC and its influence on the microstructural, tribological, and corrosion properties of a TiC-reinforced metal matrix composites
Mohr, A. and Röttger, A. and Theisen, W.
Journal of Composite Materials 51 3611-3621 (2017)Ferro-Titanit® is a metal matrix composite (MMC) with a high wear and corrosion resistance. It contains TiC as hard particles on account of their high hardness, good corrosion resistance, and low density. This wear- and corrosion-resistant material is amenable to machining in the soft-annealed state, which gives rise to chips containing a large amount of the expensive TiC hard particles. Due to the cost of TiC, there is great interest in recycling the TiC from these chips so that it can be reused in the production of further Ferro-Titanit® materials. In this study, the recycled TiC [(Ti,X)C] is investigated with regard to morphology, particle size, chemical composition, and phases, and the results were compared to industrially produced TiC. In the next step, the (Ti,X)C was reused in the production of new Ferro-Titanit®. The Ferro-Titanit® reinforced with (Ti,X)C was also characterized with respect to microstructure, wear behavior, and corrosion resistance. Our investigations identified a change in the chemical composition of the TiC as a result of diffusion processes and a decrease in TiC particle size with respect to the initial state. The change in morphology and size of TiC during the recycling process influences the microstructure and the material behavior of the MMC containing recycled TiC. © 2017, © The Author(s) 2017.
view abstract doi: 10.1177/0021998317692032 2017 • 276 Comparative ignition tests of coal under oxy-fuel conditions in a standardized laboratory test rig
Becker, A. and Schiemann, M. and Scherer, V. and Shaddix, C. and Haxter, D. and Mayer, J.
Fuel 208 127-136 (2017)Ignitability is important to characterize pulverized coal combustion, as it is directly related to flame stability. The current work describes a practical test rig for rapid laboratory analysis of pulverized coal cloud ignition properties. The system has been designed for conventional coal combustion conditions using air as the oxidant. In the current work, the measurement principle of the device is described and its adaption to and applicability for oxy-fuel combustion tests is demonstrated. Four coals with different rank were measured in air and in oxy-fuel atmospheres containing 20–35 vol% O2 in CO2. The major influencing factors for the investigated samples were found to be the coal rank and the gas-phase oxygen concentration, while a minor influence of particle size was observed. © 2017 Elsevier Ltd
view abstract doi: 10.1016/j.fuel.2017.06.129 2017 • 275 Continuous Synthesis of γ-Valerolactone in a Trickle-Bed Reactor over Supported Nickel Catalysts
Hengst, K. and Ligthart, D.A.J.M. and Doronkin, D.E. and Walter, K.M. and Kleist, W. and Hensen, E.J.M. and Grunwaldt, J.-D.
Industrial and Engineering Chemistry Research 56 2680-2689 (2017)Various Ni-based catalysts were tested in the continuous liquid phase hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) in a trickle-bed reactor using water as solvent with the aim to develop an economic and environmentally friendly way for the GVL synthesis. For this purpose, various synthesis methods were used to prepare Ni-based catalysts, which were first screened in batch reactors. Characterization by X-ray diffraction, temperature-programmed reduction, electron microscopy, hydrogen chemisorption, and X-ray absorption spectroscopy showed that slow precipitation using urea resulted in a good Ni dispersion. The dispersion also improved at lower Ni loading, and smaller Ni particles mostly showed an enhanced catalytic performance for the synthesis of GVL. 5 wt % Ni/Al2O3 prepared by wet impregnation showed the highest specific activity for the hydrogenation of LA to GVL (90% LA conversion and 75% GVL yield) featuring an average Ni particle size of 6 nm. Some deactivation of the catalysts was observed, probably due to transformation of γ-Al2O3 to boehmite and sintering of the Ni particles. In addition, reoxidation of Ni particles may additionally lead to deactivation as concluded by comparison with screening studies in batch reactors. (Graph Presented). © 2017 American Chemical Society.
view abstract doi: 10.1021/acs.iecr.6b03493 2017 • 274 Development of synthetic slag with marble waste and calcium aluminate agents for cast iron desulfurization
Grillo, F.F. and Coleti, J.L. and De Oliveira, J.R. and Junca, E. and Deike, R. and Espinosa, D.C.R.
Materials Research 20 1230-1237 (2017)The aim of this work was to study the use of slags to desulfurize cast iron. It was proposed to use alumina instead of fluorspar. In addition, marble waste was used instead of lime. Simulations applying Thermo-Calc® software were carried out in order to obtain the theoretical phases using thermodynamic data. Then, a comparison between theoretical data and experimental tests were performed. Cast iron was melted in induction furnace at 1550ºC. Slags composed mainly for CaO and Al2O3 were used to desulfurize cast iron. The results showed that the desulphurization reaction was favored when the liquid phase was increased. Furthermore, it was found that cast iron desulfurization occurs by top slag mechanism. Furthermore, the desulfurization tests showed a decrease up to 90.10% in the sulfur content to the mixture containing conventional lime and 87.25% to the mixture RMF15. The slags obtained from marble waste contained MgO, which it interfered negatively in the desulfurization yield. In addition, increasing the CaO particle diameter improved the desulfurization process. The desulphurization process more favored to particle size of 500-1000 µm.
view abstract doi: 10.1590/1980-5373-MR-2016-0834 2017 • 273 Diagnostics of Cold-Sprayed Particle Velocities Approaching Critical Deposition Conditions
Mauer, G. and Singh, R. and Rauwald, K.-H. and Schrüfer, S. and Wilson, S. and Vaßen, R.
Journal of Thermal Spray Technology 1-11 (2017)In cold spraying, the impact particle velocity plays a key role for successful deposition. It is well known that only those particles can achieve successful bonding which have an impact velocity exceeding a particular threshold. This critical velocity depends on the thermomechanical properties of the impacting particles at impacting temperature. The latter depends on the gas temperature in the torch but also on stand-off distance and gas pressure. In the past, some semiempirical approaches have been proposed to estimate particle impact and critical velocities. Besides that, there are a limited number of available studies on particle velocity measurements in cold spraying. In the present work, particle velocity measurements were performed using a cold spray meter, where a laser beam is used to illuminate the particles ensuring sufficiently detectable radiant signal intensities. Measurements were carried out for INCONEL® alloy 718-type powders with different particle sizes. These experimental investigations comprised mainly subcritical spray parameters for this material to have a closer look at the conditions of initial deposition. The critical velocities were identified by evaluating the deposition efficiencies and correlating them to the measured particle velocity distributions. In addition, the experimental results were compared with some values estimated by model calculations. © 2017 ASM International
view abstract doi: 10.1007/s11666-017-0596-8 2017 • 272 Enhanced Crystallization of Lysozyme Mediated by the Aggregation of Inorganic Seed Particles
Weichsel, U. and Segets, D. and Thajudeen, T. and Maier, E.-M. and Peukert, W.
Crystal Growth and Design 17 967-981 (2017)We show that aggregation plays a major role in seeded growth of protein crystals. The seeded batch approach provides the opportunity to set the starting conditions for protein crystallization by adding a defined amount of well-characterized seed particles. The experimental observations for tetragonal hen egg-white lysozyme (LSZ) confirm the concept of the oriented aggregation of larger building blocks to form a protein crystal. It was shown that the aggregation of the seed particles/bioconjugates is advantageous for the product quality in terms of larger and more defined LSZ crystals and in terms of accelerated reaction kinetics. We present a population balance (PB) model for the seeded batch crystallization of LSZ considering the aggregation of growth units to form protein crystals. For the modeling of crystal growth, evolving particle size distributions (PSDs) of agglomerating LSZ molecules were measured by dynamic light scattering (DLS). Moreover, the aggregation of seed particles in LSZ solutions under crystallization conditions was investigated by DLS. In line with our expectations, the number of seeds was found to be important as it strongly affects the collision frequency in the aggregation term of our PB model. Finally, the applied model gives trends of the supersaturation depletion curves and orders of magnitude of the measured CSDs in particle size correctly, ranging from only a few nanometers up to micrometer-sized particles/crystals. Thus, by the combination of PB modeling and experimentally determined crystallization parameters, insights into the crystal formation mechanism were obtained. To the best of our knowledge, this is the first attempt to model growth within a crystal population by an aggregation mechanism induced by seeding with foreign particles. © 2016 American Chemical Society.
view abstract doi: 10.1021/acs.cgd.6b01026 2017 • 271 Experimental and numerical study of a HMDSO-seeded premixed laminar low-pressure flame for SiO2 nanoparticle synthesis
Feroughi, O.M. and Deng, L. and Kluge, S. and Dreier, T. and Wiggers, H. and Wlokas, I. and Schulz, C.
Proceedings of the Combustion Institute 36 1045-1053 (2017)Silicon dioxide nanoparticles are generated in a lean hydrogen/oxygen flat flame doped with small amounts of hexamethyldisiloxane (HMDSO) stabilized by a water-cooled sintered bronze matrix. The burner is housed in an optically-accessible low-pressure (3kPa) chamber. Temperature fields were determined via multi-line laser-induced fluorescence (LIF) using added NO as target species. Gas-phase silicon oxide (SiO) was detected via laser-induced fluorescence (LIF) by exciting the weakly temperature-dependent rovibrational Q11(32) transition in the A-X (0,0) vibronic band system at 235.087nm. Semi-quantitative concentration profiles as a function of height-above-burner (HAB) were obtained after exploiting the measured temperature fields and correcting measured LIF intensities for the temperature-dependence of the ground-state population and collisional quenching using measured effective fluorescence lifetimes. Particle sizes were determined as a function of HAB via molecular-beam sampling with subsequent particle mass spectrometry (PMS). The experimental data were used to develop a simple kinetics model of HMDSO combustion and SiO2 particle precursor formation with subsequent nucleation and particle growth in the H2/O2 flame. The model was incorporated in a CFD simulation to account for facility effects that arise from modified flow fields and heat transfer between the flame and the reactor chamber. © 2016 Elsevier Ltd.
view abstract doi: 10.1016/j.proci.2016.07.131 2017 • 270 Experimental identification of unique angular dependent scattering behavior of nanoparticles
Yin, G. and Song, M. and Raja, W. and Andrae, P. and Schmid, M.
Journal of the European Optical Society 13 (2017)Background: Nanoparticles exhibit unique light scattering properties and are applied in many research fields. Methods: In this work, we perform angular resolved scattering measurements to study the scattering behaviour of random and periodic silver (Ag), and periodic polystyrene (PS) nanoparticles. Results: The random Ag nanoparticles, with a wide particle size distribution, are able to broadbandly scatter light into large angles. In contrast, both types of periodic nanoparticles are characterized by a strong scattering zone where scattering angles are increasing as the wavelength increases. Conclusions: Angular resolved scattering measurements enable experimentally revealing the particular scattering properties of different nanostructures. © 2017, The Author(s).
view abstract doi: 10.1186/s41476-017-0066-4 2017 • 269 Fabrication of Oxide Dispersion Strengthened Bond Coats with Low Al2O3 Content
Bergholz, J. and Pint, B.A. and Unocic, K.A. and Vaßen, R.
Journal of Thermal Spray Technology 1-12 (2017)Nanoscale oxide dispersions have long been used to increase the oxidation and wear resistance of alloys used as bond coatings in thermal barrier coatings. Their manufacturing via mechanical alloying is often accompanied by difficulties regarding their particle size, homogeneous distribution of the oxide dispersions inside the powder, involving considerable costs, due to cold welding of the powder during milling. A significant improvement in this process can be achieved by the use of process control agent (PCA) to achieve the critical balance between cold welding and fracturing, thereby enhancing the process efficiency. In this investigation, the influence of the organic additive stearic acid on the manufacturing process of Al2O3-doped CoNiCrAlY powder was investigated. Powders were fabricated via mechanical alloying at different milling times and PCA concentrations. The results showed a decrease in particle size, without hindering the homogeneous incorporation of the oxide dispersions. Two powders manufactured with 0.5 and 1.0 wt.% PCA were deposited by high velocity oxygen fuel (HVOF) spraying. Results showed that a higher content of elongated particles in the powder with the higher PCA content led to increased surface roughness, porosity and decreased coating thickness, with areas without embedded oxide particles. © 2017 ASM International
view abstract doi: 10.1007/s11666-017-0550-9 2017 • 268 High activity and negative apparent activation energy in low-temperature CO oxidation - Present on Au/Mg(OH)2, absent on Au/TiO2
Wang, Y. and Widmann, D. and Wittmann, M. and Lehnert, F. and Gu, D. and Schüth, F. and Behm, R.J.
Catalysis Science and Technology 7 4145-4161 (2017)Aiming at a better understanding of the unusual low-temperature CO oxidation reaction behavior on Au/Mg(OH)2 catalysts, we investigated this reaction mainly by combined kinetic and in situ IR spectroscopy measurements over a wide range of temperatures, from -90 °C to 200 °C. Catalysts with a very narrow Au particle size distribution were prepared by colloidal deposition. Kinetic measurements, performed under differential, dry reaction conditions at different constant temperatures, enabled the separation of thermal and deactivation effects. They revealed that the distinct reaction behavior, with an exceptionally high activity at temperatures below 0 °C and decreasing CO oxidation rates in the range between -50 °C and 30 °C, equivalent to a negative apparent activation energy, does not result from either deactivation effects or H2O trace impurities, but is an intrinsic feature of the reaction. An unusual temperature dependence was also observed for the tendency for deactivation, with a pronounced maximum at -20 °C, which mainly results from an accumulation of surface carbonate species blocking active reaction sites or access of adsorbed reactants to them. Similar measurements on Au/TiO2 catalysts revealed that the high activity of Au/Mg(OH)2 in the low-temperature range compared to Au/TiO2 is first of all due to the weaker interactions of Mg(OH)2 with CO2 compared to TiO2. This leads to an increasing tendency of CO2 product molecules to adsorb on the latter catalyst at reaction temperatures below 0 °C and hence to rapid 'self-poisoning' with CO2 desorption as the rate-limiting step. For Au/Mg(OH)2, CO2 desorption is much faster, allowing much higher rates in the continuous CO oxidation. Based on temporal analysis of products (TAP) reactor measurements, the decay of the reaction rates in the range -50 °C to +50 °C is tentatively attributed to a decreasing steady-state coverage of weakly bound molecularly adsorbed O2 with increasing temperature, while stable adsorbed active surface oxygen is negligible over the entire range of reaction temperatures investigated. The implications of these and earlier findings for the mechanistic understanding of the low-temperature CO oxidation on Au/Mg(OH)2 and support effects therein are discussed. © The Royal Society of Chemistry 2017.
view abstract doi: 10.1039/c7cy00722a 2017 • 267 High productive and continuous nanoparticle fabrication by laser ablation of a wire-target in a liquid jet
Kohsakowski, S. and Santagata, A. and Dell'Aglio, M. and de Giacomo, A. and Barcikowski, S. and Wagener, P. and Gökce, B.
Applied Surface Science 403 487-499 (2017)To scale-up pulsed laser ablation in liquids for nanoparticle synthesis, we combine two promising approaches, a wire-shaped target and a small liquid layer, in one setup. Using thin liquid layers a significant increase in nanoparticle productivity (up to 5 times) is obtained. This increase is attributed to the dynamics, shape of the cavitation bubble and the spring-board like behavior of the wires in the small liquid filament. It is found that despite the increase in productivity, the particle size is independent of the productivity-related ablation parameters such as repetition rate, liquid layer thickness and wire diameter. In addition to the cavitation bubble, further shielding effects have been related to both, the laser ablated material and the presence of generated small vapor bubbles. The obtained results show that this setup can provide a good strategy to realize a continuous and process-stable (particle size and quality) ablation process without the need of target replacement. © 2017 Elsevier B.V.
view abstract doi: 10.1016/j.apsusc.2017.01.077 2017 • 266 Impact of processing conditions and feedstock characteristics on thermally sprayed MCrAlY bondcoat properties
Mauer, G. and Sebold, D. and Vaßen, R. and Hejrani, E. and Naumenko, D. and Quadakkers, W.J.
Surface and Coatings Technology 318 114-121 (2017)One of the options to manufacture MCrAlY bondcoats (M. =Co, Ni) for thermal barrier coating systems is High Velocity Oxy-Fuel spraying (HVOF). In this work, particle diagnostics were applied to investigate the impact of processing conditions and feedstock characteristics on the relevant bondcoat properties. The results showed that compromises must be made on the oxygen/fuel ratio, spray distance, and particle size distribution to strike a balance between low oxidation and dense microstructures.These limitations initiated the development of the High Velocity Atmospheric Plasma Spray process (HV-APS) as a further alternative process. In this work, HV-APS process parameters were developed for a three cathode torch in combination with a 5. mm diameter high speed nozzle. A one-dimensional calculation of the expansion through this nozzle to atmospheric pressure yielded supersonic conditions with a Mach number of 1.84. The calculated plasma temperatures at the nozzle exit and in the expanded jet are 8400. K and slightly above 5200. K, respectively, which is low compared to conventional APS processes. A very fine powder with a median particle size of 18. μm was identified to be most suitable. Although the spray conditions were relatively cold, reasonable deposition efficiencies up to 61% and rather dense coatings were achieved using this feedstock. The as-sprayed porosity was ≈. 2% which was reduced by the subsequent vacuum heat treatment to <. 1%. The oxygen content determined by chemical analysis for a sample sprayed at a spray distance of 100. mm was 0.41. ±. 0.04. wt%.Moreover, reference samples were manufactured by Low Pressure Plasma Spraying (LPPS). The oxidation behavior was compared in isothermal and cyclic oxidation tests. The oxidation rates of the HV-APS coatings were found to be significantly lower than those of LPPS coatings. The thermally grown oxide scale showed less yttrium incorporation and better adherence in case of HV-APS. The latter is suggested to be related to a unique new distribution of Y-rich nano-sized oxide precipitates. The cyclic oxidation test confirmed the better oxidation resistance of the HV-APS coatings. © 2016 Elsevier B.V.
view abstract doi: 10.1016/j.surfcoat.2016.08.079 2017 • 265 Key parameters for the radiative emittance of ashes of solid fuels
Gorewoda, J. and Scherer, V.
Energy Procedia 120 181-188 (2017)The knowledge of the emittance of solid fuel ashes is important for the radiative energy balance in boilers and, hence, crucial for their design. This paper summarizes the most important effects on emittance based on own experiments and makes references to literature. Experimental results will be presented on the spectral emittance of typical minerals (SiO2, CaCO3, MgCO3, SrCO3, CaSO4, MgSO4, Fe2O3) contained in solid fuels ashes, extended by exemplary measurements on natural ashes (coal). The normal emittance is measured in a temperature range between 500 and 1000 °C in the wavelength range from 1.6 to 12 μm in a radiation test rig. The influence of physical surface structure and chemical-mineralogical composition on emittance is discussed. The results show that sizes of ash particles influences emittance. Emittance is increasing with particle size. Surface sintering as well as Fe in the ash also increases emittance. Surface fusion can either increase or decrease emittance based on ash composition. Sulfates and carbonates, typical for ashes under oxyfuel conditions, show characteristic spectral emittance bands. These bands vanish when the sulfates and carbonates being converted to the corresponding oxides at elevated temperatures. These characteristic bands can also be detected in natural ashes which consist of a variety of mineral components. © 2017 The Authors. Published by Elsevier Ltd.
view abstract doi: 10.1016/j.egypro.2017.07.163 2017 • 264 Land use regression modeling of oxidative potential of fine particles, NO2, PM2.5 mass and association to type two diabetes mellitus
Hellack, B. and Sugiri, D. and Schins, R.P.F. and Schikowski, T. and Krämer, U. and Kuhlbusch, T.A.J. and Hoffmann, B.
Atmospheric Environment 171 181-190 (2017)While land use regression models (LUR) are commonly used, e.g. for the prediction of spatially variable air pollutant mass concentrations, they are scarcely used for predicting the oxidative potential (OP), a suggested unifying predictor of health effects. Therefore a LUR model was developed to examine if long-term OP of fine particulate exposure can be reasonably predicted by LUR modeling and whether it is related to health effects in a study region comprised of urban and rural areas. Four 14-day sampling periods over 1 year at 40 sites in the western Ruhr Area and adjacent northern rural area, Germany, in 2002/2003 were conducted and annual Nitrogen Dioxide (NO2), fine particles (PM2.5), and OP were calculated. LUR models were developed to estimate spatially-resolved annual OP, NO2 and PM2.5 concentrations. The model performance was checked by leave-one-out cross validation (LOOCV) and cox regression was used to analyze the association of modeled residential OP and NO2 with incident type 2 diabetes mellitus (T2DM) in 1784 elderly women during a mean follow-up of 16 years (baseline 1985–1994). The measured OP and NO2 concentrations were moderately correlated (rSpearman 0.57). The LUR models explained 62% and 92% of the OP and NO2 variance (adjusted LOOCV R2 57% and 90%). PM10 emission from combustion in a 5000 m buffer was the most important predictor for OP and NO2. Modeled pollutants were highly correlated (rSpearman 0.87). Model quality for OP was sensitive to the inclusion of a single influential measurement site. For PM2.5 mass only an insufficient model with a low explained variance of 22% (adjusted R2) was developed so no health effects analyses were conducted with estimated PM2.5. Increases in OP and NO2 were associated with an increase in risk of T2DM by a hazard ratio of 1.38 (95% CI 1.06–1.80) and 1.39 (95% CI 1.07–1.81) per interquartile range of OP and NO2, respectively. We conclude that spatially-resolved OP can be predicted by LUR modeling, but future work is needed to investigate the possibility to increase OP model quality with refined predictors. © 2017 Elsevier Ltd
view abstract doi: 10.1016/j.atmosenv.2017.10.017 2017 • 263 Large eddy simulation of particle aggregation in turbulent jets
Pesmazoglou, I. and Kempf, A.M. and Navarro-Martinez, S.
Journal of Aerosol Science 111 1-17 (2017)Aggregation is an inter-particle process that involves a multitude of different physical and chemical mechanisms. Aggregation processes often occur within turbulent flows; for example in spray drying, soot formation, or nanoparticle formation. When the concentration of particles is very large, a direct simulation of individual particles is not possible and alternative approaches are needed. The present work follows the stochastic aggregation modelling based on a Lagrangian framework by Pesmazoglou, Kempf, and Navarro-Martinez (2016) and implements it in the Large Eddy Simulation context. The new coupled model is used to investigate particle aggregation in turbulent jets. Two cases are considered: an existent Direct Numerical Simulation of nanoparticle agglomeration in a planar jet and an experimental configuration of SiO2 nanoparticles in a round jet. The results show a good agreement in both cases, demonstrating the advantages of the Lagrangian framework to model agglomeration and it capacity to describe the full particle size distribution. © 2017 Elsevier Ltd
view abstract doi: 10.1016/j.jaerosci.2017.06.002 2017 • 262 Large eddy simulations of nanoparticle synthesis from flame spray pyrolysis
Rittler, A. and Deng, L. and Wlokas, I. and Kempf, A.M.
Proceedings of the Combustion Institute 36 1077-1087 (2017)Large eddy simulations of the nanoparticle synthesis from flame spray pyrolysis are presented. A standard reactor is investigated, with ethanol/hexamethyldisiloxane (HMDSO) mixture as spray/precursor composition and oxygen as dispersion gas for the production of silica nanoparticles. Spray evaporation, ignition and stabilisation of the flame are achieved by a premixed methane/oxygen pilot flame. The gas, spray and nanoparticle phases are modelled with Eulerian, Lagrangian and Eulerian approaches, respectively. A modified tabulated chemistry model, adapted from the premixed flamelet generated manifold approach (PFGM) with artificial flame thickening (ATF) is proposed, tested and applied for the system. The control variables are the element mass fractions of hydrogen and carbon together with a joint progress variable. The population balance equation of the nanoparticles is modelled in terms of number, volume and surface area concentration, its subfilter distribution is modelled with a delta function. The combustion of HMDSO and formation of silica particle monomers is described by a two-step global mechanism. The nucleation source term is tabulated as a function of the control variables. The submodels for spray and combustion are validated separately to compensate for the shortage in detailed experimental data for nanoparticle spray flames. Subsequently, simulation results for the particles are presented and discussed, in particular the polydisperse particle size distributions resulting from turbulence. © 2016 The Combustion Institute.
view abstract doi: 10.1016/j.proci.2016.08.005 2017 • 261 Liquid filtration of nanoparticles through track-etched membrane filters under unfavorable and different ionic strength conditions: Experiments and modeling
Lee, H. and Segets, D. and Süß, S. and Peukert, W. and Chen, S.-C. and Pui, D.Y.H.
Journal of Membrane Science 524 682-690 (2017)Nanoparticle deposition experiments under unfavorable conditions were conducted experimentally and theoretically. The 0.2 and 0.4 µm rated track-etched membrane filters were challenged with 60, 100, 147, 220, 350 and 494 nm polystyrene latex (PSL) particles with different ionic strengths ranging from 0.005 to 0.05 M. The capillary tube model, with replacing the viscosity of air to water, was used to estimate the initial efficiency, or the transport efficiency of the particles to the filter surface, which was corrected in a second step by allowing the detachment of the nanoparticles according to the sum of adhesive and hydrodynamic torques. The adhesive torques were derived from surface interactions accessed by the extended DLVO theory. Calculation results showed that the adhesive torque of a particle located in the calculated primary minimum was slightly larger than the hydrodynamic torque, resulting in particle deposition. However, experimental data clearly indicated that detachment occurred. This could only be explained by the presence of additional hydration forces, leading to a larger separation which became relevant at high ionic strengths. By including hydration into our theoretical framework, experiment and theory were in very good agreement under all different ionic strength conditions. The findings allow a basic understanding of surface interactions between nanoparticles and membranes in micro- and ultra-filtration applications for drinking water production, wastewater treatment and particle free water production in industries. © 2016 Elsevier B.V.
view abstract doi: 10.1016/j.memsci.2016.11.023 2017 • 260 Local photocurrent mapping and cell performance behaviour on a nanometre scale for monolithically interconnected Cu(In,Ga)Se2 solar cells
Haggui, M. and Reinhold, B. and Andrae, P. and Greiner, D. and Schmid, M. and Fumagalli, P.
Journal of Microscopy 268 66-72 (2017)The local efficiency of lamellar shaped Cu(In,Ga)Se2 solar cells has been investigated using scanning near-field optical microscopy (SNOM). Topographic and photocurrent measurements have been performed simultaneously with a 100 nm tip aperture. The lamellar shaped solar cell with monolithic interconnects (P scribe) has been investigated on a nanometre scale for the first time at different regions using SNOM. It was found that, the cell region between P1 and P2 significantly contributes to the solar cells overall photocurrent generation. The photocurrent produced depends locally on the sample topography and it is concluded that it is mainly due to roughness changes of the ZnO:Al/i-ZnO top electrode. Regions lying under large grains of ZnO produce significantly less current than regions under small granules. The observed photocurrent features were allocated primarily to the ZnO:Al/i-ZnO top electrode. They were found to be independent of the wavelength of the light used (532 nm and 633 nm). © 2017 The Authors Journal of Microscopy © 2017 Royal Microscopical Society
view abstract doi: 10.1111/jmi.12587 2017 • 259 Magnetic polaron on dangling-bond spins in CdSe colloidal nanocrystals
Biadala, L. and Shornikova, E.V. and Rodina, A.V. and Yakovlev, D.R. and Siebers, B. and Aubert, T. and Nasilowski, M. and Hens, Z. and Dubertret, B. and Efros, A.L. and Bayer, M.
Nature Nanotechnology 12 569-574 (2017)Non-magnetic colloidal nanostructures can demonstrate magnetic properties typical for diluted magnetic semiconductors because the spins of dangling bonds at their surface can act as the localized spins of magnetic ions. Here we report the observation of dangling-bond magnetic polarons (DBMPs) in 2.8-nm diameter CdSe colloidal nanocrystals (NCs). The DBMP binding energy of 7 meV is measured from the spectral shift of the emission lines under selective laser excitation. The polaron formation at low temperatures occurs by optical orientation of the dangling-bond spins (DBSs) that result from dangling-bond-assisted radiative recombination of spin-forbidden dark excitons. Modelling of the temperature dependence of the DBMP-binding energy and emission intensity shows that the DBMP is composed of a dark exciton and about 60 DBSs. The exchange integral of one DBS with the electron confined in the NC is ∼0.12 meV. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
view abstract doi: 10.1038/nnano.2017.22 2017 • 258 Mass spectrometric analysis of clusters and nanoparticles during the gas-phase synthesis of tungsten oxide
Kluge, S. and Wiggers, H. and Schulz, C.
Proceedings of the Combustion Institute 36 1037-1044 (2017)The combustion synthesis of nanoscale tungsten-oxide particles from tungsten hexafluoride is investigated in a low-pressure hydrogen/oxygen flat flame. The reactor is equipped with molecular-beam sampling of post-flame gases at variable height above burner (HAB). Main species of the flame, intermediate tungsten species, and tungsten-oxide clusters are studied with time-of-flight mass spectrometry (TOF-MS) as a function of HAB. Various WO x (OH) y are identified within the flame front. With increasing HAB, (WO3) n clusters with increasing cluster size appear in the burnt gases at the expense of the concentration of W1 species. Clusters with n =3-7 arise at 70mm HAB, followed by larger clusters at even larger heights. Clusters up to (WO3)38 were identified. The subsequent formation of nanoparticles is detected with particle mass spectrometry (PMS) and a quartz crystal microbalance (QCM) from 120mm HAB and the increasing particle size and mass flux have been determined. © 2016.
view abstract doi: 10.1016/j.proci.2016.06.165 2017 • 257 Nanoparticulate versus ionic silver: Behavior in the tank water, bioaccumulation, elimination and subcellular distribution in the freshwater mussel Dreissena polymorpha
Zimmermann, S. and Ruchter, N. and Loza, K. and Epple, M. and Sures, B.
Environmental Pollution 222 251-260 (2017)Zebra mussels (Dreissena polymorpha) were exposed to polyvinylpyrrolidone (PVP)-coated silver nanoparticles (AgNP; hydrodynamic diameter 80 nm; solid diameter 50 nm) to investigate the behavior of Ag in the tank water with respect to its uptake, bioaccumulation, elimination and subcellular distribution in the mussel soft tissue. Parallel experiments were performed with ionic Ag (AgNO3) to unravel possible differences between the metal forms. The recovery of the applied Ag concentration (500 μg/L) in the tank water was clearly affected by the metal source (AgNP < AgNO3) and water type (reconstituted water < tap water). Filtration (< 0.45 μm) of water samples showed different effects on the quantified metal concentration depending on the water type and Ag form. Ag accumulation in the mussel soft tissue was neither influenced by the metal source nor by the water type. Ag concentrations in the mussel soft tissue did not decrease during 14 days of depuration. For both metal forms the Ag distribution within different subcellular fractions, i.e. metal-rich granules (MRG), cellular debris, organelles, heat-sensitive proteins (HSP) and metallothionein-like proteins (MTLP), revealed time-dependent changes which can be referred to intracellular Ag translocation processes. The results provide clear evidence for the uptake of Ag by the mussel soft tissue in nanoparticulate as well as in ionic form. Thus, zebra mussels could be used as effective accumulation indicators for environmental monitoring of both Ag forms. © 2016 Elsevier Ltd.
view abstract doi: 10.1016/j.envpol.2016.12.048 2017 • 256 Normal Radiative Emittance of Coal Ash Sulfates in the Context of Oxyfuel Combustion
Gorewoda, J. and Scherer, V.
Energy and Fuels 31 4400-4406 (2017)Oxyfuel ashes are supposed to form more sulfates than ashes from air-fired systems. This can be caused by the increased SO2 concentrations due to intensive flue gas recirculation in oxyfuel systems. Therefore, we investigated the spectral emittance characteristics of typical mineral sulfates in coal ashes, namely Mg and Ca sulfates. The samples were prepared in powder form. Two particle size fractions were examined (x < 32 μm and 125 < x < 160 μm). The powders were investigated concerning their temperature-dependent normal emittance in a radiation test rig. Spectral measurements by a Fourier transform infrared spectrometer in the temperature range from 500 to 1000 °C were carried out. The results reveal that Ca and Mg sulfates show characteristic S-O absorption bands in the wavelength regions from 3 to 4 μm, from 4.5 to 6 μm, and from 8 to 9.5 μm. MgSO4 transforms to MgO at around 930 °C. The total emittance of the oxide is significantly reduced by Δε = 0.15 compared to the sulfate. The small size fractions MgSO4 and CaSO4 undergo sintering when being heated, which influences emittance. An increase of total emittance up to a value of Δε = 0.08 is detected for CaSO4. Finally, it is shown that emittance increases with particle size (Δε in total emittance approximately = 0.1). © 2017 American Chemical Society.
view abstract doi: 10.1021/acs.energyfuels.6b02866 2017 • 255 Resolved simulations of single char particle combustion in a laminar flow field
Farazi, S. and Sadr, M. and Kang, S. and Schiemann, M. and Vorobiev, N. and Scherer, V. and Pitsch, H.
Fuel 201 15-28 (2017)The aim of this work is to study spatially and chemically resolved particle combustion cases to understand chemical and laminar transport processes and to support model development. In the present study, the combustion process of a single char particle located in air or oxy-fuel atmosphere composed of oxygen, carbon dioxide, and steam is investigated. Char burnout is represented in highly resolved numerical simulations including a detailed description of the surface and the gas phase chemistry. At the solid-gas interface, heat and mass fluxes due to the surface reactions involving carbon oxidation and gasification are considered. The model is validated based on experimental results for char burnout phase in a flat flame burner. We perform a comprehensive set of fully resolved reactive 2-D simulations by varying particle size, relative velocity, diluent, and oxygen composition in the surrounding gas. The simulation results are discussed regarding the CO2 and N2 content of the atmosphere highlighting the effects of oxy-fuel combustion. Furthermore, the impact of the particle flow motion on the flame that forms around the char particle is investigated by varying relative Reynolds number with particle size and relative slip velocity. © 2016 Elsevier Ltd
view abstract doi: 10.1016/j.fuel.2016.11.011 2017 • 254 Sand-blasting treatment as a way to improve the adhesion strength of hydroxyapatite coating on titanium implant
Grubova, I. and Priamushko, T. and Surmeneva, M. and Korneva, O. and Epple, M. and Prymak, O. and Surmenev, R.
Journal of Physics: Conference Series 830 (2017)In the current study, the effect of corundum particle sizes (50 and 250-320 μm) used for sand-blasting on the structure, roughness, wettability, mechanical properties, and adhesion of radio frequency magnetron hydroxyapatite coating deposited on treated titanium substrate is studied. Morphology analysis revealed that pretreatment uniformly deforms the surface and induces the formation of pits, which size depends linearly on the grit size. The deposited coatings (Ca/P was in a range of 1.75-1.79) are homogeneous and repeat the relief of the substrate (mean roughness Ra is 1.9±0.1 (250-320 μm) and 0.8±0.1 μm (50 μm)). Texture coefficient calculations revealed the predominant (002) growth texture of hydroxyapatite coatings. The resistance of the coating to plastic deformation and the surface hardening were significantly higher for coatings formed on sand blasted with particle size of 50 μm. Scratch test have shown the significant improvement of wear resistance and lower friction coefficient of coatings for smoother samples. Dynamic contact angle measurements revealed the hydrophilic properties of the hydroxyapatite coating. Thus, sand-blasting of titanium with corundum powder having the size of 50 μm prior to the deposition of RF magnetron coating is recommended for the medical applications intended to improve the bonding between the substrate and coating.
view abstract doi: 10.1088/1742-6596/830/1/012109 2017 • 253 Shape memory micro-and nanowire libraries for the high-throughput investigation of scaling effects
Oellers, T. and König, D. and Kostka, A. and Xie, S. and Brugger, J. and Ludwig, Al.
ACS Combinatorial Science 19 574-584 (2017)The scaling behavior of Ti-Ni-Cu shape memory thin-film micro- and nanowires of different geometry is investigated with respect to its influence on the martensitic transformation properties. Two processes for the highthroughput fabrication of Ti-Ni-Cu micro- to nanoscale thin film wire libraries and the subsequent investigation of the transformation properties are reported. The libraries are fabricated with compositional and geometrical (wire width) variations to investigate the influence of these parameters on the transformation properties. Interesting behaviors were observed: Phase transformation temperatures change in the range from 1 to 72 °C (austenite finish, (Af), 13 to 66 °C (martensite start, Ms) and the thermal hysteresis from -3.5 to 20 K. It is shown that a vanishing hysteresis can be achieved for special combinations of sample geometry and composition. © 2017 American Chemical Society.
view abstract doi: 10.1021/acscombsci.7b00065 2017 • 252 Size Quenching during Laser Synthesis of Colloids Happens Already in the Vapor Phase of the Cavitation Bubble
Letzel, A. and Gökce, B. and Wagener, P. and Ibrahimkutty, S. and Menzel, A. and Plech, A. and Barcikowski, S.
Journal of Physical Chemistry C 121 5356-5365 (2017)Although nanoparticle synthesis by pulsed laser ablation in liquids (PLAL) is gaining wide applicability, the mechanism of particle formation, in particular size-quenching effects by dissolved anions, is not fully understood yet. It is well-known that the size of small primary particles (d ≤ 10 nm), secondary particles (spherical particles d > 10 nm), and agglomerates observed ex situ is effectively reduced by the addition of small amounts of monovalent electrolyte to the liquid prior to laser ablation. In this study, we focus on the particle formation and evolution inside the vapor filled cavitation bubble. This vapor phase is enriched with ions from the afore added electrolyte. By probing the cavitation bubbles' interior by means of small-angle X-ray scattering (SAXS), we are able to examine whether the size quenching reaction between nanoparticles and ions starts already during cavitation bubble confinement or if these reactions are subjected to the liquid phase. We find that particle size quenching occurs already within the first bubble oscillation (approximately 100 μs after laser impact), still inside the vapor phase. Thereby we demonstrate that nanoparticle-ion interactions during PLAL are in fact a gas phase phenomenon. These interactions include size reduction of both primary and secondary particles and a decreased abundance of the latter as shown by in situ SAXS and confirmed by ex situ particle analysis (e.g., static SAXS and TEM). (Figure Presented). © 2017 American Chemical Society.
view abstract doi: 10.1021/acs.jpcc.6b12554 2017 • 251 Size- and density-controlled deposition of Ag nanoparticle films by a novel low-temperature spray chemical vapour deposition method—research into mechanism, particle growth and optical simulation
Liu, Y. and Plate, P. and Hinrichs, V. and Köhler, T. and Song, M. and Manley, P. and Schmid, M. and Bartsch, P. and Fiechter, S. and Lux-Steiner, M.C. and Fischer, C.-H.
Journal of Nanoparticle Research 19 (2017)Ag nanoparticles have attracted interest for plasmonic absorption enhancement of solar cells. For this purpose, well-defined particle sizes and densities as well as very low deposition temperatures are required. Thus, we report here a new spray chemical vapour deposition method for producing Ag NP films with independent size and density control at substrate temperatures even below 100 °C, which is much lower than for many other techniques. This method can be used on different substrates to deposit Ag NP films. It is a reproducible, low-cost process which uses trimethylphosphine (hexafluoroacetylacetonato) silver as a precursor in alcoholic solution. By systematic variation of deposition parameters and classic experiments, mechanisms of particle growth and of deposition processes as well as the low decomposition temperature of the precursor could be explained. Using the 3D finite element method, absorption spectra of selected samples were simulated, which fitted well with the measured results. Hence, further applications of such Ag NP films for generating plasmonic near field can be predicted by the simulation. © 2017, Springer Science+Business Media Dordrecht.
view abstract doi: 10.1007/s11051-017-3834-6 2016 • 250 A review on lithium combustion
Schiemann, M. and Bergthorson, J. and Fischer, P. and Scherer, V. and Taroata, D. and Schmid, G.
Applied Energy 162 948-965 (2016)Lithium combustion has been studied for several decades, with a primary focus on safety issues, such as lithium fires resulting from spills in nuclear reactors. Several studies have also considered the use of lithium as a fuel within propellants, or within propulsion systems that burn lithium in the atmospheric "air" of other planets. Lithium safety has typically been investigated through combustion of molten pieces of lithium or within pool fires. For propulsion applications, experiments were carried out using packed beds of lithium particles.A novel approach that has recently been proposed is the use of lithium as a recyclable fuel, or energy carrier that can compactly store renewable energy. In this scheme, lithium is burned with air, or power-plant exhaust, to generate heat for thermal power systems when power is needed. The solid-phase combustion products would be collected and recycled, via electrolysis, back into elemental lithium when excess renewable power is available.This paper summarizes the existing knowledge on lithium combustion. It presents the available findings on lithium combustion for large single pieces of lithium, on pool fires, reaction in packed beds, as well as the combustion of sub-mm sized particles and droplets which are needed for the use of lithium as an energy carrier. The combustion reactions of lithium with O2, H2O, CO2 and N2 are discussed. Modelling of lithium-particle combustion is at the early stages of development and available results are discussed. © 2015.
view abstract doi: 10.1016/j.apenergy.2015.10.172 2016 • 249 An experimental study of ultrafiltration for sub-10nm quantum dots and sub-150 nm nanoparticles through PTFE membrane and Nuclepore filters
Chen, S.-C. and Segets, D. and Ling, T.-Y. and Peukert, W. and Pui, D.Y.H.
Journal of Membrane Science 497 153-161 (2016)Ultrafiltration techniques (pore size of membrane below 100nm) are widely used in chemical engineering, semiconductor, pharmaceutical, food and beverage industries. However, for small particles, which are more and more attracting interests, the pore size often does not correlate well with sieving characteristics of the ultra-membranes. This may cause serious issues during modeling and prediction of retention efficiencies. Herein, a series of liquid filtration experiments with unfavorable conditions were performed. PTFE membranes (50, 100nm) and Nuclepore filters (50, 400nm) were challenged with 1.7nm manganese doped ZnS and 6.6 nm ZnO quantum dots (QDs), 12.4, 34.4 and 50 nm Au and 150 nm SiO2 nanoparticles. For larger and medium sized particles, sieving and eventually pore blockage phenomena were observed. In comparison, for small QDs, a high initial retention efficiency (>0.4) in both filters was monitored, followed by a reduced efficiency with ongoing particle loading. This high initial retention of small nanoparticles was attributed to diffusion deposition rather than to sieving since the ratio of pore size to particle size was significantly high (up to 58). Our experimental results allow a basic understanding of the deposition mechanism of small nanoparticles (diffusion vs. sieving) in different filter structures. © 2015 Elsevier B.V.
view abstract doi: 10.1016/j.memsci.2015.09.022 2016 • 248 Analysis of particle size distributions of quantum dots: From theory to application
KONA Powder and Particle Journal 2016 48-62 (2016)Small, quantum-confined semiconductor nanoparticles, known as quantum dots (QDs) are highly important material systems due to their unique optoelectronic properties and their pronounced structure-property relationships. QD applications are seen in the emerging fields of thin films and solar cells. In this review, different characterization techniques for particle size distributions (PSDs) will be summarized with special emphasis on strategies developed and suggested in the past to derive data on the dispersity of a sample from optical absorbance spectra. The latter use the assumption of superimposed individual optical contributions according to the relative abundance of different sizes of a colloidal dispersion. In the second part, the high potential of detailed PSD analysis to get deeper insights of typical QD processes such as classification by size selective precipitation (SSP) will be demonstrated. This is expected to lead to an improved understanding of colloidal surface properties which is of major importance for the development of assumption-free interaction models. © 2016 Hosokawa Powder Technology Foundation.
view abstract doi: 10.14356/kona.2016012 2016 • 247 Barium sulfate micro- and nanoparticles as bioinert reference material in particle toxicology
Loza, K. and Föhring, I. and Bünger, J. and Westphal, G.A. and Köller, M. and Epple, M. and Sengstock, C.
Nanotoxicology 10 1492-1502 (2016)The inhalation of particles and their exposure to the bronchi and alveoli constitute a major public health risk. Chemical as well as particle-related properties are important factors for the biological response but are difficult to separate from each other. Barium sulfate is a completely inert chemical compound, therefore it is ideally suited to separate these two factors. The biological response of rat alveolar macrophages (NR8383) was analyzed after exposure to barium sulfate particles with three different diameters (40 nm, 270 nm, and 1.3 μm, respectively) for 24 h in vitro (particle concentrations from 12.5 to 200 μg mL− 1). The particles were colloidally stabilized as well as fluorescently-labeled by carboxymethylcellulose, conjugated with 6-aminofluorescein. All kinds of barium sulfate particles were efficiently taken up by NR8383 cells and found inside endo-lysosomes, but never in the cell nucleus. Neither an inflammatory nor a cytotoxic response was detected by the ability of dHL-60 and NR8383 cells to migrate towards a chemotactic gradient (conditioned media of NR8383 cells) and by the release of inflammatory mediators (CCL2, TNF-α, IL-6). The particles neither caused apoptosis (up to 200 μg mL− 1) nor necrosis (up to 100 μg mL− 1). As only adverse reaction, necrosis was found at a concentration of 200 μg mL− 1 of the largest barium sulfate particles (1.3 μm). Barium sulfate particles are ideally suited as bioinert control to study size-dependent effects such as uptake mechanisms of intracellular distributions of pure particles, especially in nanotoxicology. © 2016 Informa UK Limited, trading as Taylor & Francis Group.
view abstract doi: 10.1080/17435390.2016.1235740 2016 • 246 Barrierless growth of precursor-free, ultrafast laser-fragmented noble metal nanoparticles by colloidal atom clusters - A kinetic in situ study
Jendrzej, S. and Gökce, B. and Amendola, V. and Barcikowski, S.
Journal of Colloid and Interface Science 463 299-307 (2016)Unintended post-synthesis growth of noble metal colloids caused by excess amounts of reactants or highly reactive atom clusters represents a fundamental problem in colloidal chemistry, affecting product stability or purity. Hence, quantified kinetics could allow defining nanoparticle size determination in dependence of the time. Here, we investigate in situ the growth kinetics of ps pulsed laser-fragmented platinum nanoparticles in presence of naked atom clusters in water without any influence of reducing agents or surfactants. The nanoparticle growth is investigated for platinum covering a time scale of minutes to 50 days after nanoparticle generation, it is also supplemented by results obtained from gold and palladium. Since a minimum atom cluster concentration is exceeded, a significant growth is determined by time resolved UV/Vis spectroscopy, analytical disc centrifugation, zeta potential measurement and transmission electron microscopy. We suggest a decrease of atom cluster concentration over time, since nanoparticles grow at the expense of atom clusters. The growth mechanism during early phase (<1. day) of laser-synthesized colloid is kinetically modeled by rapid barrierless coalescence. The prolonged slow nanoparticle growth is kinetically modeled by a combination of coalescence and Lifshitz-Slyozov-Wagner kinetic for Ostwald ripening, validated experimentally by the temperature dependence of Pt nanoparticle size and growth quenching by Iodide anions. © 2015.
view abstract doi: 10.1016/j.jcis.2015.10.032 2016 • 245 Co3O4 Nanoparticles Supported on Mesoporous Carbon for Selective Transfer Hydrogenation of α,β-Unsaturated Aldehydes
Wang, G.-H. and Deng, X. and Gu, D. and Chen, K. and Tüysüz, H. and Spliethoff, B. and Bongard, H.-J. and Weidenthaler, C. and Schmidt, W. and Schüth, F.
Angewandte Chemie - International Edition 55 11101-11105 (2016)A simple and scalable method for synthesizing Co3O4nanoparticles supported on the framework of mesoporous carbon (MC) was developed. Benefiting from an ion-exchange process during the preparation, the cobalt precursor is introduced into a mesostructured polymer framework that results in Co3O4nanoparticles (ca. 3 nm) supported on MC (Co3O4/MC) with narrow particle size distribution and homogeneous dispersion after simple reduction/pyrolysis and mild oxidation steps. The as-obtained Co3O4/MC is a highly efficient catalyst for transfer hydrogenation of α,β-unsaturated aldehydes. Selectivities towards unsaturated alcohols are always higher than 95 % at full conversion. In addition, the Co3O4/MC shows high stability under the reaction conditions, it can be recycled at least six times without loss of activity. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract doi: 10.1002/anie.201604673 2016 • 244 Continuous synthesis of nanostructured silica based materials in a gas-liquid segmented flow tubular reactor
Knossalla, J. and Mezzavilla, S. and Schüth, F.
New Journal of Chemistry 40 4361-4366 (2016)A continuous synthesis of several spherical silica structures-by means of a gas-liquid segmented flow tubular reactor-is reported. Specifically, as proof of concept, we showed that 300-400 nm mesoporous core-shell spheres (SiO2@mSiO2), mesoporous spheres (mSiO2) as well gold-encapsulated spheres (Au@SiO2) can be effectively produced in a continuous manner in a tubular reactor. Thus, the successful conversion of classical batch methods to continuous processes opens new possibilities for the up-scaled synthesis of advanced nanostructured materials. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2016.
view abstract doi: 10.1039/c5nj03033a 2016 • 243 Deagglomeration testing of airborne nanoparticle agglomerates: Stability analysis under varied aerodynamic shear and relative humidity conditions
Ding, Y. and Stahlmecke, B. and Kaminski, H. and Jiang, Y. and Kuhlbusch, T.A.J. and Riediker, M.
Aerosol Science and Technology 50 1253-1263 (2016)Occupational exposure to nanomaterial aerosols poses potential health risks to workers at nanotechnology workplaces. Understanding the mechanical stability of airborne nanoparticle agglomerates under varied mechanical forces and environmental conditions is important for estimating their emission potential and the released particle size distributions, which in consequence alters their transport and human uptake probability. In this study, two aerosolization and deagglomeration systems were used to investigate the potential for deagglomeration of nanopowder aerosols with different surface hydrophilicity under a range of shear forces and relative humidity conditions. Critical orifices were employed to subject airborne agglomerates to the shear forces induced by a pressure drop. Increasing applied pressure drop was found to be associated with decreased mean particle size and increased particle number concentrations. Rising humidity decreased the deagglomeration tendency as expressed by larger modal particle sizes and lower number concentrations compared to dry conditions. Hydrophilic aerosols exhibited higher sensitivities to changes in humidity than hydrophobic particles. However, the test systems themselves also differed in generated particle number concentrations and size distributions, which in turn altered the responses of created aerosols to humidity changes. The results of the present study clearly demonstrate that (a) humidity control is essential for dustiness and deagglomeration testing, (b) that (industrial) deagglomeration, for example, for preparation of aerosol suspensions, can be manipulated by subjecting airborne particles to external energies, and (c) that the humidity of workplace air may be relevant when assessing occupational exposure to nanomaterial aerosols. Copyright © 2016 American Association for Aerosol Research © 2016 American Association for Aerosol Research.
view abstract doi: 10.1080/02786826.2016.1216072 2016 • 242 Detection of individual nanoparticle impacts using etched carbon nanoelectrodes
Clausmeyer, J. and Wilde, P. and Löffler, T. and Ventosa, E. and Tschulik, K. and Schuhmann, W.
Electrochemistry Communications 73 67-70 (2016)A rapid and reliable nanofabrication route produces electrodes with beneficial properties for electrochemistry based on stochastic nanoparticle collision events. Carbon nanoelectrodes are etched to expose conical carbon tips which present an increased surface area for the detection of nanoparticle impacts. The tuneable electrode size as well as the conical geometry allow to increase the observed particle impact frequency while maintaining low background noise. Moreover, anodic particle coulometry for the sizing of silver nanoparticles shows that the detected impacts are representative of the polydisperse particle population. © 2016
view abstract doi: 10.1016/j.elecom.2016.11.003 2016 • 241 Devolatilization and volatiles reaction of individual coal particles in the context of FGM tabulated chemistry
Knappstein, R. and Kuenne, G. and Ketelheun, A. and Köser, J. and Becker, L. and Heuer, S. and Schiemann, M. and Scherer, V. and Dreizler, A. and Sadiki, A. and Janicka, J.
Combustion and Flame 169 72-84 (2016)The method of Flamelet Generated Manifolds (FGM) is coupled with a coal devolatilization model to perform transient simulations of a well-defined single coal particle combustion experiment for the first time. The gas phase chemistry is mapped onto a three-dimensional manifold controlled by the mixture fraction, a reaction progress variable and the enthalpy. A simulation of an electrically heated inert pyrolysis reactor is performed in order to evaluate transferability and applicability of experimentally obtained devolatilization kinetic parameters to Large Eddy Simulation (LES) codes for combustion configurations. Finally, the FGM modeling approach is applied to a premixed flat flame configuration, in which the coal particles cross a laminar flame front and are exposed to the hot gases. Numerical results regarding the volatiles reaction are compared to experimental findings. Particle and gas phase states are studied. Overall, good agreement between numerical results and experimental findings regarding the volatiles ignition range could be observed. © 2016 The Combustion Institute.
view abstract doi: 10.1016/j.combustflame.2016.04.014 2016 • 240 Effect of Ni Content on Structural and Magnetic Properties of Li-Ni Ferrites Nanostructure Prepared by Hydrothermal Method
Al-Shakarchi, E.K. and Lafta, S.H. and Musa, A.M. and Farle, M. and Salikov, R.
Journal of Superconductivity and Novel Magnetism 29 923-929 (2016)Li-Ni ferrite with chemical formula Li0.5−0.5xNixFe2.5−0.5xO4 was prepared by hydrothermal method with different Ni contents (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0) using metal chlorides, ferrous sulfate and sodium hydroxide as oxidants. The hydrothermal treatment was accomplished at (155 ∘ C) for (3 h). The required analyses of XRD, FTIR, SEM, TEM, EDX and magnetic hysteresis loop were performed to characterize the complete behavior as a function of x. It was found that lattice constant has a small increase as x increased. Crystallite size had a minimum value of about 13 nm at x = 1.0 and maximum value of about 33 nm at x = 0.3. It was also found that XRD density increased as x was increased. The particle size distributions showed that the maximum value is around 22 nm. FTIR analysis showed the presence of two main peaks with some shifting. Nanospheres were the predominant particles beside the presence of low nanorod concentration. M-H loops had super paramagnetic shape. The coercivity had a minimum value at x = 0.5. The magnetic saturation had a maximum value at x = 0.3, and the initial susceptibility χi had a maximum value at x = 0.5. © 2015, Springer Science+Business Media New York.
view abstract doi: 10.1007/s10948-015-3334-9 2016 • 239 Electrophoretic deposition of ligand-free platinum nanoparticles on neural electrodes affects their impedance in vitro and in vivo with no negative effect on reactive gliosis
Angelov, S.D. and Koenen, S. and Jakobi, J. and Heissler, H.E. and Alam, M. and Schwabe, K. and Barcikowski, S. and Krauss, J.K.
Journal of Nanobiotechnology 14 (2016)Background: Electrodes for neural stimulation and recording are used for the treatment of neurological disorders. Their features critically depend on impedance and interaction with brain tissue. The effect of surface modification on electrode impedance was examined in vitro and in vivo after intracranial implantation in rats. Electrodes coated by electrophoretic deposition with platinum nanoparticles (NP; <10 and 50 nm) as well as uncoated references were implanted into the rat's subthalamic nucleus. After postoperative recovery, rats were electrostimulated for 3 weeks. Impedance was measured before implantation, after recovery and then weekly during stimulation. Finally, local field potential was recorded and tissue-to-implant reaction was immunohistochemically studied. Results: Coating with NP significantly increased electrode's impedance in vitro. Postoperatively, the impedance of all electrodes was temporarily further increased. This effect was lowest for the electrodes coated with particles <10 nm, which also showed the most stable impedance dynamics during stimulation for 3 weeks and the lowest total power of local field potential during neuronal activity recording. Histological analysis revealed that NP-coating did not affect glial reactions or neural cell-count. Conclusions: Coating with NP <10 nm may improve electrode's impedance stability without affecting biocompatibility. Increased impedance after NP-coating may improve neural recording due to better signal-to-noise ratio. © 2016 Angelov et al.
view abstract doi: 10.1186/s12951-015-0154-9 2016 • 238 Formation of Well-Defined Polymer Particles in the Sub-100 nm Size Range by Using Amphiphilic Block Copolymer Surfactants and a Microemulsion Approach
Kampmann, A.-L. and Luksin, M. and Pretzer, I. and Weberskirch, R.
Macromolecular Chemistry and Physics 217 1704-1711 (2016)Here, the formation of nanoparticles based on a microemulsion approach and the use of polymer surfactants are described. Therefore, two amphiphilic poly(2-oxazoline) block copolymers P1 and P2 with alkyne groups in their hydrophobic block have been synthesized by ring-opening, cationic polymerization. The polymers P1 and P2 are employed in a microemulsion process to stabilize the particle core by core cross-linking of 1,6-hexanediol diacrylate (HDDA) using either AIBN as azo-initiator or 2-propanethiol as a photo-initiator for the polymerization reaction. The results show that particle size can be controlled by sonication time, the hydrophilic–hydrophobic balance of the polymer surfactant, and the ratio of polymer surfactant versus HDDA giving access to water-soluble nanoparticles in a size range of 10–70 nm. (Figure presented.). © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract doi: 10.1002/macp.201600108 2016 • 237 Gene transfection of human mesenchymal stem cells with a nano-hydroxyapatite–collagen scaffold containing DNA-functionalized calcium phosphate nanoparticles
Tenkumo, T. and Vanegas Sáenz, J.R. and Takada, Y. and Takahashi, M. and Rotan, O. and Sokolova, V. and Epple, M. and Sasaki, K.
Genes to Cells 21 682-695 (2016)This study aimed to fabricate a growth factor-releasing biodegradable scaffold for tissue regeneration. We prepared multishell calcium phosphate (CaP) nanoparticles functionalized with DNA, polyethyleneimine (PEI), protamine and octa-arginine (R8) and compared their respective transfection activity and cell viability measures using human mesenchymal stem cells. DNA–protamine complexes improved the transfection efficiency of CaP nanoparticles with the exception of those functionalized with R8. These complexes also greatly reduced the cytotoxicity of PEI. In addition, we also fabricated DNA–protamine-functionalized CaP nanoparticle-loaded nano-hydroxyapatite–collagen scaffolds and investigated their gene transfection efficiencies. These experiments showed that the scaffolds were associated with moderate hMSC cell viability and were capable of releasing the BMP-2 protein into hMSCs following gene transfection. In particular, the scaffold loaded with protamine-containing CaP nanoparticles showed the highest cell viability and transfection efficiency in hMSCs; thus, it might be suitable to serve as an efficient growth factor-releasing scaffold. © 2016 Molecular Biology Society of Japan and John Wiley & Sons Australia, Ltd
view abstract doi: 10.1111/gtc.12374 2016 • 236 Granule size distributions after twin-screw granulation – Do not forget the feeding systems
Meier, R. and Thommes, M. and Rasenack, N. and Moll, K.-P. and Krumme, M. and Kleinebudde, P.
European Journal of Pharmaceutics and Biopharmaceutics 106 59-69 (2016)The aim of this study was to investigate the influence of qualitatively different powder feeder performances on resulting granule size distributions after twin-screw granulation of a highly drug loaded, hydrophobic mixture and a mannitol powder. It was shown that powder feeder related problems usually cannot be identified by trusting in the values given by the feeder. Therefore, a newly developed model for the evaluation of the performance of powder feeders was introduced and it was tried to connect this model to residence time distributions in twin-screw granulation processes. The influence of feeder performances on resulting granule size distributions varied, depending on the applied screw configuration and the used powder. Regarding the hydrophobic and highly drug loaded formulation, which was granulated at an L/S-ratio of 0.5, a pure conveying screw and a medium kneading configuration, consisting of 60° kneading blocks were negatively influenced by poor feeder settings. For optimal settings more narrow distributions could be obtained. For an extensive kneading configuration good and poor settings resulted in mono-modal granule size distributions but were differing in the overall size. Mannitol, a model substance for a liquid sensitive formulation was granulated at an L/S-ratio of 0.075. It was even more important to maintain optimal feeding as mannitol was highly affected by poor feeder performances. Even an extensive kneading configuration could not level the errors in powder feeder performance, resulting in qualitatively different granule size distributions. The results of this study demonstrate the importance of detailed knowledge about applied feeding systems to gain optimal performance in twin-screw granulation. © 2016 Elsevier B.V.
view abstract doi: 10.1016/j.ejpb.2016.05.011 2016 • 235 High temperature stability study of carbon supported high surface area catalysts—Expanding the boundaries of ex-situ diagnostics
Polymeros, G. and Baldizzone, C. and Geiger, S. and Grote, J.P. and Knossalla, J. and Mezzavilla, S. and Keeley, G.P. and Cherevko, S. and Zeradjanin, A.R. and Schüth, F. and Mayrhofer, K.J.J.
Electrochimica Acta 211 744-753 (2016)The performance of proton-exchange membrane fuel cells (PEMFCs) is defined by the equally important parameters of the intrinsic activity and stability of the electrocatalysts. This work focuses on the stability of carbon supported high surface area oxygen reduction reaction catalysts at potentials and temperatures similar to the operating conditions of PEMFCs. The catalysts used for this investigation consist of Pt nanoparticles of the same particle size supported on two types of carbon support having different textural properties, i.e., Vulcan and Hollow Graphitic Spheres (HGS). A broad toolbox of characterization techniques is utilized at 60 °C in order to resolve the contribution of the different degradation mechanisms, namely nanoparticle coalescence, metal dissolution and the corrosion of carbon support, to the total active surface area loss. The results obtained by investigating the impact of temperature, potential treatment and catalyst layer morphology on the aging behavior lead to a deeper understanding of the aging mechanisms and their interrelation at application-relevant conditions. Moreover, the previously reported improved performance of the Pt/HGS catalyst is confirmed also under higher temperatures. The experimental approach introduced in this work, highlights new challenges for high-temperature degradation investigations with supported PEMFC catalyst. © 2016 Elsevier Ltd
view abstract doi: 10.1016/j.electacta.2016.06.105 2016 • 234 Highly selective plasma-activated copper catalysts for carbon dioxide reduction to ethylene
Mistry, H. and Varela, A.S. and Bonifacio, C.S. and Zegkinoglou, I. and Sinev, I. and Choi, Y.-W. and Kisslinger, K. and Stach, E.A. and Yang, J.C. and Strasser, P. and Cuenya, B.R.
Nature Communications 7 (2016)There is an urgent need to develop technologies that use renewable energy to convert waste products such as carbon dioxide into hydrocarbon fuels. Carbon dioxide can be electrochemically reduced to hydrocarbons over copper catalysts, although higher efficiency is required. We have developed oxidized copper catalysts displaying lower overpotentials for carbon dioxide electroreduction and record selectivity towards ethylene (60%) through facile and tunable plasma treatments. Herein we provide insight into the improved performance of these catalysts by combining electrochemical measurements with microscopic and spectroscopic characterization techniques. Operando X-ray absorption spectroscopy and cross-sectional scanning transmission electron microscopy show that copper oxides are surprisingly resistant to reduction and copper+ species remain on the surface during the reaction. Our results demonstrate that the roughness of oxide-derived copper catalysts plays only a partial role in determining the catalytic performance, while the presence of copper+ is key for lowering the onset potential and enhancing ethylene selectivity.
view abstract doi: 10.1038/ncomms12123 2016 • 233 Influence of agglomeration and specific lung lining lipid/protein interaction on short-term inhalation toxicity
Wohlleben, W. and Driessen, M.D. and Raesch, S. and Schaefer, U.F. and Schulze, C. and Vacano, B.V. and Vennemann, A. and Wiemann, M. and Ruge, C.A. and Platsch, H. and Mues, S. and Ossig, R. and Tomm, J.M. and Schnekenburger, J. ...
Nanotoxicology 10 970-980 (2016)Abstract: Lung lining fluid is the first biological barrier nanoparticles (NPs) encounter during inhalation. As previous inhalation studies revealed considerable differences between surface functionalized NPs with respect to deposition and toxicity, our aim was to investigate the influence of lipid and/or protein binding on these processes. Thus, we analyzed a set of surface functionalized NPs including different SiO2 and ZrO2 in pure phospholipids, CuroSurfTM and purified native porcine pulmonary surfactant (nS). Lipid binding was surprisingly low for pure phospholipids and only few NPs attracted a minimal lipid corona. Additional presence of hydrophobic surfactant protein (SP) B in CuroSurfTM promoted lipid binding to NPs functionalized with Amino or PEG residues. The presence of the hydrophilic SP A in nS facilitated lipid binding to all NPs. In line with this the degree of lipid and protein affinities for different surface functionalized SiO2 NPs in nS followed the same order (SiO2 Phosphate ∼ unmodified SiO2 < SiO2 PEG < SiO2 Amino NPs). Agglomeration and biomolecule interaction of NPs in nS was mainly influenced by surface charge and hydrophobicity. Toxicological differences as observed in short-term inhalation studies (STIS) were mainly influenced by the core composition and/or surface reactivity of NPs. However, agglomeration in lipid media and lipid/protein affinity appeared to play a modulatory role on short-term inhalation toxicity. For instance, lipophilic NPs like ZrO2, which are interacting with nS to a higher extent, exhibited a far higher lung burden than their hydrophilic counterparts, which deserves further attention to predict or model effects of respirable NPs. © 2016 Informa UK Limited, trading as Taylor & Francis Group.
view abstract doi: 10.3109/17435390.2016.1155671 2016 • 232 Influence of carbonate decomposition on normal spectral radiative emittance in the context of oxyfuel combustion
Gorewoda, J. and Scherer, V.
Energy and Fuels 30 9752-9760 (2016)To investigate whether the radiative properties of carbonate rich ash layers in oxyfuel combustion systems might be influenced by the carbonate decomposition to the corresponding oxide, the emittance of Sr, Mg, and Ca carbonates is examined. In addition “synthetic coal ashes” were produced from mixtures of CaCO3 and SiO2 as well as Fe2O3 and SiO2. The mixture ratios of the minerals were varied. All samples were prepared from powders with known particle size fractions of x < 32 μm and 125 < 160 μm. The powders were investigated for their temperature-dependent normal emittance in a radiation test rig by FT-IR spectroscopy in the temperature range from 500 to 1000 °C. The results reveal that the phase transformation from the carbonate to the corresponding oxide has a significant influence on spectral emittance. Whereas the carbonates show characteristic peaks in spectral emittance around 4 μm which stem from the infrared active CO3 group, these peaks vanish after transformation to the oxide. For CaCO3, the most prominent carbonate in typical coal ashes, the emittance of the oxide is significantly lower than for the carbonate. Such a behavior in terms of total and spectral emittance has also been detected, for example, examining a Ca rich Rhenish lignite. Emittance increases with particle size for all samples. An enrichment of SiO2 with Fe2O3 leads to an increase in emittance. © 2016 American Chemical Society
view abstract doi: 10.1021/acs.energyfuels.6b01398 2016 • 231 Influence of temperature, pressure, and cooling rate during hot isostatic pressing on the microstructure of an SX Ni-base superalloy
Mujica Roncery, L. and Lopez-Galilea, I. and Ruttert, B. and Huth, S. and Theisen, W.
Materials and Design 97 544-552 (2016)This work investigates the application of hot isostatic pressing for heat treatment of the single-crystal Ni-base superalloy ERBO/1. Recent progress regarding incorporation of quenching within hot isostatic pressing enables heat treatments to be performed so that the microstructures can be frozen at a desired point. The influence of the temperature, pressure, and cooling method (quenching, natural convection, and slow cooling) as well as the cooling rate after solutioning-HIP treatment on pore densification and γ/. γ'-morphology was measured. Temperatures above γ'-solvus resulted in a greater efficiency of the porosity reduction. At super-solvus temperatures, pressures above 75. MPa are sufficient enough to annihilate the porosity. The cooling rate after HIP-solutioning treatment has a major influence on the γ'-particle size and shape. Quenching with 45-20. K/s at 100. MPa leads to high number density and monomodal distribution of γ'-particles with sizes around 140. nm. In contrast, slow cooling rate of 0.33. K/s leads to γ'-precipitate sizes of 720. nm. Moreover, an integrated heat treatment at 100. MPa, which consisted of solutioning and aging in the HIP, was successfully applied. It led to smaller γ'-particle sizes and narrower γ-channels compared to the conventionally heat-treated material and also almost no porosity. © 2016 Elsevier Ltd.
view abstract doi: 10.1016/j.matdes.2016.02.051 2016 • 230 Laser-based in situ embedding of metal nanoparticles into bioextruded alginate hydrogel tubes enhances human endothelial cell adhesion
Blaeser, A. and Million, N. and Campos, D.F.D. and Gamrad, L. and Köpf, M. and Rehbock, C. and Nachev, M. and Sures, B. and Barcikowski, S. and Fischer, H.
Nano Research 9 3407-3427 (2016)Alginate is a widely used hydrogel in tissue engineering owing to its simple and non-cytotoxic gelation process, ease of use, and abundance. However, unlike hydrogels derived from mammalian sources such as collagen, alginate does not contain cell adhesion ligands. Here, we present a novel laser ablation technique for the in situ embedding of gold and iron nanoparticles into hydrogels. We hypothesized that integration of metal nanoparticles in alginate could serve as an alternative material because of its chemical biofunctionalization ability (coupling of RGD ligands) to favor cell adhesion. Cytocompatibility and biofunctionality of the gels were assessed by cell culture experiments using fibroblasts and endothelial cells. Nanoparticles with an average particle size of 3 nm (gold) and 6 nm (iron) were generated and stably maintained in alginate for up to 6 months. Using an extrusion system, several centimeter-long alginate tubes with an outer diameter of approximately 3 mm and a wall thickness of approximately 150 μm were manufactured. Confocal microscopy revealed homogeneously distributed nanoparticle agglomerates over the entire tube volume. Endothelial cells seeded on iron-loaded gels showed significantly higher viability and an increased degree of spreading, and the number of attached cells was also elevated in comparison to the control and gold-loaded alginates. We conclude that laser-based in situ integration of iron nanoparticles (≤ 0.01 wt.%) in alginate is a straightforward method to generate composite materials that favor the adhesion of endothelial cells. In addition, we show that nanoparticle integration does not impair the alginate’s gelation and 3D biofabrication properties. [Figure not available: see fulltext.] © 2016, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.
view abstract doi: 10.1007/s12274-016-1218-3 2016 • 229 Metastable high-entropy dual-phase alloys overcome the strength-ductility trade-off
Li, Z. and Pradeep, K.G. and Deng, Y. and Raabe, D. and Tasan, C.C.
Nature 534 227-230 (2016)Metals have been mankind's most essential materials for thousands of years; however, their use is affected by ecological and economical concerns. Alloys with higher strength and ductility could alleviate some of these concerns by reducing weight and improving energy efficiency. However, most metallurgical mechanisms for increasing strength lead to ductility loss, an effect referred to as the strength-ductility trade-off. Here we present a metastability-engineering strategy in which we design nanostructured, bulk high-entropy alloys with multiple compositionally equivalent high-entropy phases. High-entropy alloys were originally proposed to benefit from phase stabilization through entropy maximization. Yet here, motivated by recent work that relaxes the strict restrictions on high-entropy alloy compositions by demonstrating the weakness of this connection, the concept is overturned. We decrease phase stability to achieve two key benefits: interface hardening due to a dual-phase microstructure (resulting from reduced thermal stability of the high-temperature phase); and transformation-induced hardening (resulting from the reduced mechanical stability of the room-temperature phase). This combines the best of two worlds: extensive hardening due to the decreased phase stability known from advanced steels and massive solid-solution strengthening of high-entropy alloys. In our transformation-induced plasticity-assisted, dual-phase high-entropy alloy (TRIP-DP-HEA), these two contributions lead respectively to enhanced trans-grain and inter-grain slip resistance, and hence, increased strength. Moreover, the increased strain hardening capacity that is enabled by dislocation hardening of the stable phase and transformation-induced hardening of the metastable phase produces increased ductility. This combined increase in strength and ductility distinguishes the TRIP-DP-HEA alloy from other recently developed structural materials. This metastability-engineering strategy should thus usefully guide design in the near-infinite compositional space of high-entropy alloys.
view abstract doi: 10.1038/nature17981 2016 • 228 Micropellet-loaded rods with dose-independent sustained release properties for individual dosing via the Solid Dosage Pen
Laukamp, E.J. and Knop, K. and Thommes, M. and Breitkreutz, J.
International Journal of Pharmaceutics 499 271-279 (2016)Individual dosing of medicines is relevant for paediatrics, geriatrics and personalised medicine. The Solid Dosage Pen (SDP) allows for individual dosing by cutting monolithic, tablet-like drug carriers of pre-defined heights. The aim of the present study was to develop micropellet-loaded rods (MPLRs) with dose-independent sustained release properties for individual dosing via the Solid Dosage Pen. Therefore, micropellets were successfully layered with carbamazepine and coated with polyvinyl acetate (PVAc) and PVAc/polyvinyl alcohol-polyethylene glycol (PVA-PEG). The tensile strength of the sustained release micropellets (300-450 μm) was more than two times higher (12.6-17.1 MPa) than pressures occurring during ram-extrusion of the MPLRs (below 5.8 MPa). Due to relative crystallinities above 93% for PVAc and PVA-PEG a low solubility of the coating films within the PEG-matrix was observed. The sustained release micropellets were successfully incorporated into MPLRs. Drug release properties of the pellets maintained after embedding into the matrix. Hence, the MPLRs provided dose-independent prolonged drug liberation which was not achieved for drug-loaded rods before. The MPLRs permitted the application of the SDP with a precise drug delivery from individually cut single doses. Storage stability was proven for MPLRs containing PVAc/PVA-PEG coated pellets. In conclusion, the MPLRs combined the advantages of multiparticulate dosage forms with the SDP as a device for individual dosing. © 2016 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.ijpharm.2016.01.001 2016 • 227 Nanoelectrodes reveal the electrochemistry of single nickelhydroxide nanoparticles
Clausmeyer, J. and Masa, J. and Ventosa, E. and Öhl, D. and Schuhmann, W.
Chemical Communications 52 2408-2411 (2016)Individual Ni(OH)2 nanoparticles deposited on carbon nanoelectrodes are investigated in non-ensemble measurements with respect to their energy storage properties and electrocatalysis for the oxygen evolution reaction (OER). Charging by oxidation of Ni(OH)2 is limited by the diffusion of protons into the particle bulk and the OER activity is independent of the particle size. © 2016 The Royal Society of Chemistry.
view abstract doi: 10.1039/c5cc08796a 2016 • 226 Optimization of a transferred arc reactor for metal nanoparticle synthesis
Stein, M. and Kruis, F.E.
Journal of Nanoparticle Research 18 (2016)The demand for metal nanoparticles is increasing strongly. Transferred arc synthesis is a promising process in this respect, as it shows high production rates, good quality particles and the ability of up-scaling. The influence of several process parameters on the performance of the process in terms of production rate and particle size is investigated. These parameters are the electrode design and adjustment, the gas flow rate and power input. A novel feeding mechanism allows process operation over an extended time period. It is shown that the process is capable of producing pure metal nanoparticles with variable primary particle sizes and comparatively high production rates. Optimal process conditions for a single transferred arc electrode pair are found, which allow further scale-up by numbering up. © 2016, The Author(s).
view abstract doi: 10.1007/s11051-016-3559-y 2016 • 225 Orientation of FePt nanoparticles on top of a-SiO2/Si(001), MgO(001) and sapphire(0001): Effect of thermal treatments and influence of substrate and particle size
Schilling, M. and Ziemann, P. and Zhang, Z. and Biskupek, J. and Kaiser, U. and Wiedwald, U.
Beilstein Journal of Nanotechnology 7 591-604 (2016)Texture formation and epitaxy of thin metal films and oriented growth of nanoparticles (NPs) on single crystal supports are of general interest for improved physical and chemical properties especially of anisotropic materials. In the case of FePt, the main focus lies on its highly anisotropic magnetic behavior and its catalytic activity, both due to the chemically ordered face-centered tetragonal (fct) L10 phase. If the c-axis of the tetragonal system can be aligned normal to the substrate plane, perpendicular magnetic recording could be achieved. Here, we study the orientation of FePt NPs and films on a-SiO2/Si(001), i.e., Si(001) with an amorphous (a-) native oxide layer on top, on MgO(001), and on sapphire(0001) substrates. For the NPs of an approximately equiatomic composition, two different sizes were chosen: "small" NPs with diameters in the range of 2-3 nm and "large" ones in the range of 5-8 nm. The 3 nm thick FePt films, deposited by pulsed laser deposition (PLD), served as reference samples. The structural properties were probed in situ, particularly texture formation and epitaxy of the specimens by reflection high-energy electron diffraction (RHEED) and, in case of 3 nm nanoparticles, additionally by high-resolution transmission electron microscopy (HRTEM) after different annealing steps between 200 and 650 °C. The L10 phase is obtained at annealing temperatures above 550 °C for films and 600 °C for nanoparticles in accordance with previous reports. On the amorphous surface of a-SiO2/Si substrates we find no preferential orientation neither for FePt films nor nanoparticles even after annealing at 630 °C. On sapphire(0001) supports, however, FePt nanoparticles exhibit a clearly preferred (111) orientation even in the as-prepared state, which can be slightly improved by annealing at 600-650 °C. This improvement depends on the size of NPs: Only the smaller NPs approach a fully developed (111) orientation. On top of MgO(001) the effect of annealing on particle orientation was found to be strongest. From a random orientation in the as-prepared state observed for both, small and large FePt NPs, annealing at 650 °C for 30 min reorients the small particles towards a cube-on-cube epitaxial orientation with a minor fraction of (111)-oriented particles. In contrast, large FePt NPs keep their as-prepared random orientation even after doubling the annealing period at 650 °C to 60 min. © 2016 Schilling et al.
view abstract doi: 10.3762/bjnano.7.52 2016 • 224 Permeability profile of poly(alkyl cyanoacrylate) nanocapsules
Erdmann, C. and Mayer, C.
Journal of Colloid and Interface Science 478 394-401 (2016)The permeability profile of poly(alkyl cyanoacrylate) nanocapsules is studied using pulsed-field gradient NMR on a variety of tracer molecules of different size and polarity. In addition, the influence of the surfactant layer and of organic tracer molecules on the capsule membrane permeability for water is examined. The aim of the study is a detailed understanding of the dependencies between molecular properties of a given tracer and its capability to permeate the polymer membrane. As expected, the results clearly show that the capsule membrane permeability depends on the size of the tracer molecule: the exchange rate of polyethylene glycols continuously decreases with increasing chain length. However, the permeation rate also varies with the polarity of the tracer molecule: molecules of lower polarity exchange faster than more polar ones. In turn, the capsule membrane permeability is influenced by added organic compounds. Focusing on water as a characteristic permeate and depending on the type of the additive, the permeability can be varied by almost an order of magnitude, offering an opportunity to reversibly switch the uptake and release properties of the capsules. © 2016 Elsevier Inc.
view abstract doi: 10.1016/j.jcis.2016.06.034 2016 • 223 Phase field modeling of intercalation kinetics: A finite interface dissipation approach
Zerihun, N.A. and Steinbach, I.
MRS Communications 6 270-282 (2016)When two materials interact, the processes between the phases determine the functional properties of the compound. Pivotal interface phenomena are diffusion and redistribution of atoms (molecules). This is especially of interest in Lithium ion batteries where the interfacial kinetics determines the battery performance and impact cycling stability. A new phase field model, which links the atomistic processes at the interface to the mesoscale transport by a redistribution flux controlled by the so called 'interface permeability' was developed. The model was validated with experimental data from diffusion couples. Calculations of the concentration profiles of the species at the electrode-electrolyte interface are reported. Active particle size, morphology and spatial arrangement were put in correlation with diffusion behavior for use in reverse engineering. © Materials Research Society 2016.
view abstract doi: 10.1557/mrc.2016.31 2016 • 222 Pilot-scale synthesis of metal nanoparticles by high-speed pulsed laser ablation in liquids
Streubel, R. and Bendt, G. and Gökce, B.
Nanotechnology 27 (2016)The synthesis of catalysis-relevant nanoparticles such as platinum and gold is demonstrated with productivities of 4 g h-1 for pulsed laser ablation in liquids (PLAL). The major drawback of low productivity of PLAL is overcome by utilizing a novel ultrafast high-repetition rate laser system combined with a polygon scanner that reaches scanning speeds up to 500 m s-1. This high scanning speed is exploited to spatially bypass the laser-induced cavitation bubbles at MHz-repetition rates resulting in an increase of the applicable, ablation-effective, repetition rate for PLAL by two orders of magnitude. The particle size, morphology and oxidation state of fully automated synthesized colloids are analyzed while the ablation mechanisms are studied for different laser fluences, repetition rates, interpulse distances, ablation times, volumetric flow rates and focus positions. It is found that at high scanning speeds and high repetition rate PLAL the ablation process is stable in crystallite size and decoupled from shielding and liquid effects that conventionally occur during low-speed PLAL. © 2016 IOP Publishing Ltd.
view abstract doi: 10.1088/0957-4484/27/20/205602 2016 • 221 Plasmonic Au/TiO2 nanostructures for glycerol oxidation
Dodekatos, G. and Tüysüz, H.
Catalysis Science and Technology 6 7307-7315 (2016)Au nanoparticles supported on P25 TiO2 (Au/TiO2) were prepared by a facile deposition-precipitation method with urea and investigated for surface plasmon-assisted glycerol oxidation under base-free conditions. Au/TiO2 samples were characterized in detail by X-ray diffraction, UV-vis spectroscopy, transmission electron microscopy and energy-dispersive X-ray spectroscopy. The adopted synthetic methodology permits deposition of Au nanoparticles with similar mean particle sizes up to 12.5 wt% loading that allows for the evaluation of the influence of the Au amount (without changing the particle size) on its photocatalytic performance for glycerol oxidation. The reaction conditions were optimized by carrying out a systematic study with different Au loadings on TiO2, reaction times, temperatures, catalyst amounts, O2 pressures and Au particle sizes for photocatalytic reactions as well as traditional heterogeneous catalysis. It has been shown that visible light irradiation during the reaction has a beneficial effect on the conversion of glycerol where the best catalytic results were observed for 7.5 wt% Au loading with an average particle size of around 3 nm. The main product observed, with selectivities up to 63%, was high-value dihydroxyacetone that has important industrial applications, particularly in the cosmetic industry. © 2016 The Royal Society of Chemistry.
view abstract doi: 10.1039/c6cy01192f 2016 • 220 Simultaneous Identification of Spectral Properties and Sizes of Multiple Particles in Solution with Subnanometer Resolution
Karabudak, E. and Brookes, E. and Lesnyak, V. and Gaponik, N. and Eychmüller, A. and Walter, J. and Segets, D. and Peukert, W. and Wohlleben, W. and Demeler, B. and Cölfen, H.
Angewandte Chemie - International Edition 55 11770-11774 (2016)We report an unsurpassed solution characterization technique based on analytical ultracentrifugation, which demonstrates exceptional potential for resolving particle sizes in solution with sub-nm resolution. We achieve this improvement in resolution by simultaneously measuring UV/Vis spectra while hydrodynamically separating individual components in the mixture. By equipping an analytical ultracentrifuge with a novel multi-wavelength detector, we are adding a new spectral discovery dimension to traditional hydrodynamic characterization, and amplify the information obtained by orders of magnitude. We demonstrate the power of this technique by characterizing unpurified CdTe nanoparticle samples, avoiding tedious and often impossible purification and fractionation of nanoparticles into apparently monodisperse fractions. With this approach, we have for the first time identified the pure spectral properties and band-gap positions of discrete species present in the CdTe mixture. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract doi: 10.1002/anie.201603844 2016 • 219 Size matters - The phototoxicity of TiO2 nanomaterials
Wyrwoll, A.J. and Lautenschläger, P. and Bach, A. and Hellack, B. and Dybowska, A. and Kuhlbusch, T.A.J. and Hollert, H. and Schäffer, A. and Maes, H.M.
Environmental Pollution 208 859-867 (2016)Under solar radiation several titanium dioxide nanoparticles (nano-TiO2) are known to be phototoxic for daphnids. We investigated the influence of primary particle size (10, 25, and 220 nm) and ionic strength (IS) of the test medium on the acute phototoxicity of anatase TiO2 particles to Daphnia magna. The intermediate sized particles (25 nm) showed the highest phototoxicity followed by the 10 nm and 220 nm sized particles (median effective concentrations (EC50): 0.53, 1.28, 3.88 mg/L). Photoactivity was specified by differentiating free OH radicals (therephthalic acid method) and on the other hand surface adsorbed, as well as free OH, electron holes, and O2- (electron paramagnetic resonance spectroscopy, EPR). We show that the formation of free OH radicals increased with a decrease in primary particle size (terephthalic acid method), whereas the total measured ROS content was highest at an intermediate particle size of 25 nm, which consequently revealed the highest photoxicity. The photoactivities of the 10 and 220 nm particles as measured by EPR were comparable. We suggest that phototoxicity depends additionally on the particle-daphnia interaction area, which explains the higher photoxicity of the 10 nm particles compared to the 220 nm particles. Thus, phototoxicity is a function of the generation of different ROS and the particle-daphnia interaction area, both depending on particle size. Phototoxicity of the 10 nm and 25 nm sized nanoparticles decreased as IS of the test medium increased (EC50: 2.9 and 1.1 mg/L). In conformity with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory we suggest that the precipitation of nano-TiO2 was more pronounced in high than in low IS medium, causing a lower phototoxicity. In summary, primary particle size and IS of the medium were identified as factors influencing phototoxicity of anatase nano-TiO2 to D. magna. © 2015 Elsevier Ltd. All rights reserved.
view abstract doi: 10.1016/j.envpol.2015.10.035 2016 • 218 Strong metal-support interaction and alloying in Pd/ZnO catalysts for CO oxidation
Kast, P. and Friedrich, M. and Girgsdies, F. and Kröhnert, J. and Teschner, D. and Lunkenbein, T. and Behrens, M. and Schlögl, R.
Catalysis Today 260 21-31 (2016)Pd/ZnO catalysts with different Pd content have been synthesized, thoroughly characterized and investigated with regard to their reduction behavior in hydrogen or carbon monoxide containing atmospheres, by applying CO-chemisorption, photoelectron spectroscopy, X-ray diffraction, electron microscopy, TPR and DRIFTS techniques. As a catalytic test reaction, CO-oxidation has been applied. The interaction of the noble metal with the support has been revealed in a way that can distinguish between alloying and other surface spreading/wetting phenomena, induced by strong metal-support interaction (SMSI). It was found that while alloy formation promoted CO-oxidation activity additional ZnOx formation by SMSI had the opposite effect. Zinc enrichment at the surface was detected during reduction of the catalysts, depending on the reducing agent and the Pd particle size. © 2015 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.cattod.2015.05.021 2016 • 217 Synthesis of nanosized Silicalite-1 in F-media
Jiao, K. and Xu, X. and Lv, Z. and Song, J. and He, M. and Gies, H.
Microporous and Mesoporous Materials 225 98-104 (2016)This paper reports on the successful crystallization of monodisperse, highly crystalline, nanosized zeolite Silicalite-1 crystals in fluoride media by using an active silica gel as silica source and tetrapropylammonium fluoride as structure directing agent. The synthesis procedure is hydrothermal dynamic crystallization. The silica/water ratio and synthesis temperature were reduced to optimize the number of crystal nuclei and control the rate of crystallization for obtaining nanosized zeolite crystals. Meanwhile, F- ions were used to partly replace OH- ions in the synthesis system to obtain zeolite products with high crystallinity. Analytical results of XRD-, SEM-, Dynamic Light Scanning- (DLS) IR-, Simultaneous Thermal Analysis- (STA) and N2 adsorption and desorption experiments show that the average particle size of zeolite Silicalite-1 product is about 45 nm and shows high crystallinity. The F- containing Silicalite-1 zeolite sample was compared with an industrial ZSM-5 zeolite sample and it shows obvious advantages in both reduced particle size and enhanced crystallinity. © 2015 Elsevier Inc. All rights reserved.
view abstract doi: 10.1016/j.micromeso.2015.11.043 2016 • 216 Towards a continuous adsorption process for the enrichment of ACE-inhibiting peptides from food protein hydrolysates
Hippauf, F. and Huettner, C. and Lunow, D. and Borchardt, L. and Henle, T. and Kaskel, S.
Carbon 107 116-123 (2016)Bioactive peptides such as Ile-Trp show great potential as natural ACE (angiotensin-converting-enzyme)-inhibitors. A continuous process for the up-scaled enrichment of ACE-inhibiting peptides based on a columnar adsorber system with an activated carbon stationary phase was developed. The particle size of the adsorbent and the flow rate was investigated as key factors affecting adsorption kinetics and separation performance. Batch and column adsorption experiments of model adsorbate systems were successfully transferred to a more complex system of an α-lactalbumin hydrolysate containing a multitude of species. Ile-Trp was successfully enriched from the hydrolysate by a factor of 4 using the optimized carbon column. The enrichment was more selective using smaller adsorbent particles due to improved adsorption kinetics. © 2016 Elsevier Ltd. All rights reserved.
view abstract doi: 10.1016/j.carbon.2016.05.062 2015 • 215 A data mining approach to optimize pellets manufacturing process based on a decision tree algorithm
Ronowicz, J. and Thommes, M. and Kleinebudde, P. and Krysiński, J.
European Journal of Pharmaceutical Sciences 73 44-48 (2015)The present study is focused on the thorough analysis of cause-effect relationships between pellet formulation characteristics (pellet composition as well as process parameters) and the selected quality attribute of the final product. The shape using the aspect ratio value expressed the quality of pellets. A data matrix for chemometric analysis consisted of 224 pellet formulations performed by means of eight different active pharmaceutical ingredients and several various excipients, using different extrusion/spheronization process conditions. The data set contained 14 input variables (both formulation and process variables) and one output variable (pellet aspect ratio). A tree regression algorithm consistent with the Quality by Design concept was applied to obtain deeper understanding and knowledge of formulation and process parameters affecting the final pellet sphericity. The clear interpretable set of decision rules were generated. The spehronization speed, spheronization time, number of holes and water content of extrudate have been recognized as the key factors influencing pellet aspect ratio. The most spherical pellets were achieved by using a large number of holes during extrusion, a high spheronizer speed and longer time of spheronization. The described data mining approach enhances knowledge about pelletization process and simultaneously facilitates searching for the optimal process conditions which are necessary to achieve ideal spherical pellets, resulting in good flow characteristics. This data mining approach can be taken into consideration by industrial formulation scientists to support rational decision making in the field of pellets technology. © 2015 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.ejps.2015.03.013 2015 • 214 A rapid, high-yield and large-scale synthesis of uniform spherical silver nanoparticles by a microwave-assisted polyol process
Helmlinger, J. and Heise, M. and Heggen, M. and Ruck, M. and Epple, M.
RSC Advances 5 92144-92150 (2015)Silver nanoparticles are often employed in medical devices and consumer products due to their antibacterial action. For this, reliable syntheses with quantitative yield are required. Uniform spherical silver nanoparticles with a diameter of about 180 nm were synthesized by carrying out the polyol synthesis in a microwave. Silver nitrate was dissolved in ethylene glycol and poly(N-vinyl pyrrolidone) (PVP) was added as capping agent. The particles were characterized by SEM, HRTEM, XRD, and DLS. The results are compared with the classical method where silver nitrate is reduced by glucose in aqueous solution, heated with an oil-bath. The microwave-assisted synthesis leads to an almost quantitative yield of uniform silver nanoparticles after 20 min reaction time and gives exclusively spherical particles without other shapes like triangles, rods or prisms. Diethylene glycol as solvent gave a more homogeneous particle size distribution than ethylene glycol. For both kinds of particles, dissolution in ultrapure water was examined over a period of 29 days in the presence of oxygen. The dissolution was comparable in both cases (about 50% after 4 weeks), indicating the same antibacterial action for particles from the microwave and from the glucose synthesis. © The Royal Society of Chemistry 2015.
view abstract doi: 10.1039/c5ra20446a 2015 • 213 A study on the influence of particle shape on the mechanical interactions of granular media in a hopper using the Discrete Element Method
Höhner, D. and Wirtz, S. and Scherer, V.
Powder Technology 278 286-305 (2015)In this study experimental and numerical investigations with the Discrete Element Method (DEM) on the mechanical interactions of particles with varying sphericity and aspect ratio in a rectangular hopper are conducted. In the DEM the test particles are approximated by four commonly used approximation schemes. A decrease of particle sphericity or an increase of the aspect ratio results in an more uneven, intermittend particle flow and overall lower discharge rate. It was deducted from the measurement results that changing these geometric particle properties elevates the shear strength of the particle bed and, hence, has a significant influence on the discharge properties of a hopper. Simulation results are in good general agreement with the experiments and thus demonstrate the adequacy of the DEM to predict the mechanical interactions in granular media consisting of non-spherical particles. The results presented in this study show only a minor influence of the method used to approximate particle shape within the DEM. Obviously the discharge characteristics are much stronger related to macroscopic geometric parameters than the fine scale resolution of particle geometry. © 2015 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2015.02.046 2015 • 212 Assessment of soot particle-size imaging with LII at Diesel engine conditions
Cenker, E. and Kondo, K. and Bruneaux, G. and Dreier, T. and Aizawa, T. and Schulz, C.
Applied Physics B: Lasers and Optics 119 765-776 (2015)Two-time-step laser-induced incandescence (LII) imaging was performed in Diesel engine-relevant combustion to investigate its applicability for spatially resolved measurements of soot primary particle sizes. The method is based on evaluating gated LII signals acquired with two cameras consecutively after the laser pulse and using LII modeling to deduce the particle size from the ratio of local signals. Based on a theoretical analysis, optimized detection times and durations were chosen to minimize measurement uncertainties. Experiments were conducted in a high-temperature high-pressure constant-volume pre-combustion vessel under the Engine Combustion Network’s “Spray A” conditions at 61–68 bar with additional parametric variations in injection pressure, gas temperature, and composition. The LII measurements were supported by pyrometric imaging measurements of particle heat-up temperatures. The results were compared to particle-size and size-dispersion measurements from transmission electron microscopy of soot thermophoretically sampled at multiple axial distances from the injector. The discrepancies between the two measurement techniques are discussed to analyze uncertainties and related error sources of the two diagnostics. It is found that in such environment where particles are small and pressure is high, LII signal decay times are such that LII with standard nanosecond laser and detector equipment suffers from a strong bias toward large particles. © 2015, Springer-Verlag Berlin Heidelberg.
view abstract doi: 10.1007/s00340-015-6106-0 2015 • 211 Atomic scale study of CU clustering and pseudo-homogeneous Fe-Si nanocrystallization in soft magnetic FeSiNbB(CU) alloys
Pradeep, K.G. and Herzer, G. and Raabe, D.
Ultramicroscopy 159 285-291 (2015)A local electrode atom probe has been employed to trace the onset of Cu clustering followed by their coarsening and subsequent growth upon rapid (10s) annealing of an amorphous Fe73.5Si15.5Cu1Nb3B7 alloy. It has been found that the clustering of Cu atoms introduces heterogeneities in the amorphous matrix, leading to the formation of Fe rich regions which crystallizes pseudo-homogeneously into Fe-Si nanocrystals upon annealing. In this paper, we present the data treatment method that allows for the visualization of these different phases and to understand their morphology while still quantifying them in terms of their size, number density and volume fraction. The crystallite size of Fe-Si nanocrystals as estimated from the atom probe data are found to be in good agreement with other complementary techniques like XRD and TEM, emphasizing the importance of this approach towards accurate structural analysis. In addition, a composition driven data segmentation approach has been attempted to determine and distinguish nanocrystalline regions from the remaining amorphous matrix. Such an analysis introduces the possibility of retrieving crystallographic information from extremely fine (2-4nm sized) nanocrystalline regions of very low volume fraction (< 5Vol%) thereby providing crucial in-sights into the chemical heterogeneity induced crystallization process of amorphous materials. © 2015 Elsevier B.V.
view abstract doi: 10.1016/j.ultramic.2015.04.006 2015 • 210 Bioconjugated gold nanoparticles penetrate into spermatozoa depending on plasma membrane status
Barchanski, A. and Taylor, U. and Sajti, C.L. and Gamrad, L. and Kues, W.A. and Rath, D. and Barcikowski, S.
Journal of Biomedical Nanotechnology 11 1597-1607 (2015)Spermatozoa are not only essential for animal reproduction they also represent important tools for the manipulation of animal genetics. For instance, the genetic labeling and analysis of spermatozoa could provide a prospective complementation of pre-fertilization diagnosis and could help to prevent the inheritance of defective alleles during artificial insemination or to select beneficial traits in livestock. Spermatozoa feature extremely specialized membrane organization and restricted transport mechanisms making the labeling of genetically interesting DNA-sequences, e.g., with gold nanoparticles, a particular challenge. Here, we present a systematic study on the size-related internalization of ligand-free, monovalent and bivalent polydisperse gold nanoparticles, depending on spermatozoa membrane status. While monovalent conjugates were coupled solely to either negatively-charged oligonucleotides or positively-charged cell-penetrating peptides, bivalent conjugates were functionalized with both molecules simultaneously. The results clearly indicate that the cell membrane of acrosome-intact, bovine spermatozoa was neither permeable to ligand-free or oligonucleotide-conjugated nanoparticles, nor responsive to the mechanisms of cell-penetrating peptides. Interestingly, after acrosome reaction, which comprises major changes in sperm membrane composition, fluidity and charge, high numbers of monovalent and bivalent nanoparticles were found in the postequatorial segment, depicting a close and complex correlation between particle internalization and membrane organization. Additionally, depending on the applied peptide and for nanoparticle sizes <10 nm even a successive nuclear penetration was observed, making the bivalent conjugates promising for future genetic delivery and sorting issues. Copyright © 2015 American Scientific Publishers All rights reserved.
view abstract doi: 10.1166/jbn.2015.2094 2015 • 209 Calcium phosphate nanoparticles carrying BMP-7 plasmid DNA induce an osteogenic response in MC3T3-E1 pre-osteoblasts
Hadjicharalambous, C. and Kozlova, D. and Sokolova, V. and Epple, M. and Chatzinikolaidou, M.
Journal of Biomedical Materials Research - Part A 103 3834-3842 (2015)Functionalized calcium phosphate nanoparticles with osteogenic activity were prepared. Polyethyleneimine-stabilized calcium phosphate nanoparticles were coated with a shell of silica and covalently functionalized by silanization with thiol groups. Between the calcium phosphate surface and the outer silica shell, plasmid DNA which encoded either for bone morphogenetic protein 7 (BMP-7) or for enhanced green fluorescent protein was incorporated as cargo. The plasmid DNA-loaded calcium phosphate nanoparticles were used for the transfection of the pre-osteoblastic MC3T3-E1 cells. The cationic nanoparticles showed high transfection efficiency together with a low cytotoxicity. Their potential to induce an osteogenic response by transfection was demonstrated by measuring the alkaline phosphatase (ALP) activity and calcium deposition with alizarin red staining. The expression of the osteogenic markers Alp, Runx2, ColIa1 and Bsp was investigated by means of real-time quantitative polymerase chain reaction. It was shown that phBMP-7-loaded nanoparticles can provide a means of transient transfection and localized production of BMP-7 in MC3T3-E1 cells, with a subsequent increase of two osteogenic markers, specifically ALP activity and calcium accumulation in the extracellular matrix. Future strategies to stimulate bone regeneration focus into enhancing transfection efficiency and achieving higher levels of BMP-7 produced by the transfected cells. © 2015 Wiley Periodicals, Inc.
view abstract doi: 10.1002/jbm.a.35527 2015 • 208 Catalytic hydrodeoxygenation of guaiacol over platinum supported on metal oxides and zeolites
Hellinger, M. and Carvalho, H.W.P. and Baier, S. and Wang, D. and Kleist, W. and Grunwaldt, J.-D.
Applied Catalysis A: General 490 181-192 (2015)Hydrodeoxygenation of guaiacol over Pt-based catalysts was studied as a representative for phenolic compounds in pyrolysis oil. Screening of various Pt-based catalysts supported on different oxides and using different preparation methods resulted in 1%Pt/SiO2 and platinum supported on zeolites, such as 1% Pt/H-MFI-90, as the most promising catalysts in a temperature range up to 200 ° C. Thereby conversions of 86% and 100% were received, respectively. Particularly, selectivities to cyclohexane above 90% were achieved for 1% Pt/H-MFI-90. X-ray absorption near edge structure (XANES) uncovered that mild reduction temperatures were sufficient for the reduction of 1%Pt/SiO2 (up to 150°C) and 1%Pt/H-MFI-90 (up to 40°C) while 1%Pt/Al2O3 required a higher temperature of at least 320 °C. The average particle size obtained for Pt/SiO2 was 2-3 nm as unraveled by scanning transmission electron microscopy (STEM) and extended X-ray absorption fine structure (EXAFS). The deoxygenation ability of the catalysts was improved if the Pt particles were deposited on an acidic H-MFI zeolite (>130 μmol acid sites per gram) as support. 1%Pt/SiO2 showed the highest selectivity towards deoxygenation at 50 °C, whereas for 1% Pt/H-MFI-90 temperatures of about 150 °C were required to achieve a high selectivity to cyclohexane. For the latter catalyst a longer reaction time was beneficial to maximize the selectivity towards cyclohexane. The hydrogen pressure did not have significant influence on the reaction rate. The results are in agreement with a hydrodeoxygenation mechanism over Pt/zeolite catalysts at temperatures up to 200 °C that comprises hydrogenation in the first step and acid catalyzed dehydration combined with hydrogenation in the second step. © 2014 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.apcata.2014.10.043 2015 • 207 Chemical cross-linking of polypropylenes towards new shape memory polymers
Raidt, T. and Hoeher, R. and Katzenberg, F. and Tiller, J.C.
Macromolecular Rapid Communications 36 744-749 (2015)In this work, syndiotactic polypropylene (sPP) as well as isotactic polypropylene (iPP) are cross-linked to gain a shape memory effect. Both prepared PP networks exhibit maximum strains of 700%, stored strains of up to 680%, and recoveries of nearly 100%. While x-iPP is stable for many cycles, x-sPP ruptures after the first shape-memory cycle. It is shown by wide-angle X-ray scattering (WAXS) experiments that cross-linked iPP exhibits homoepitaxy in the temporary, stretched shape but in contrast to previous reports it contains a higher amount of daughter than mother crystals. Shape memory polypropylene is prepared by cross-linking of syndiotactic as well as isotactic polypropylene (iPP). Cross-linked iPP is a shape-memory polymer with excellent stored strain, fixity-, and recovery-ratios. Wide angle X-ray scattering (WAXS) experiments reveal that the crystals in programmed x-iPP show a microstructure with mother and daughter crystals. In contrast to previous reports, the amount of daughter crystals exceeds that of the mothers. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/marc.201400727 2015 • 206 Classification of zinc sulfide quantum dots by size: Insights into the particle surface-solvent interaction of colloids
Segets, D. and Lutz, C. and Yamamoto, K. and Komada, S. and Süß, S. and Mori, Y. and Peukert, W.
Journal of Physical Chemistry C 119 4009-4022 (2015)We present a detailed study on the classification of ZnS quantum dots (QDs) by size selective precipitation (SSP). SSP allows the postsynthetic narrowing of a given feed distribution and is usually realized by titration of a poor solvent into a suspension of dispersed particles. Thereby preferred flocculation of larger structures is induced. Our results confirm that SSP is a highly robust process, following a law of mass action. That means a certain solvent composition always leads to the same ratio between coarse and fines particles with respect to a specific particle size xi. This ratio is independent of the particle size distribution (PSD) of the feed, the washing history of the particles, and the solid concentration of the particles. Regarding the illustration of our findings, we established a combined approach that takes Hansen solubility parameters (HSP) of solvent mixtures as well as changing van der Waals interactions into account. Relating both to each other, a size-dependent region of enhanced solubility is clearly identified. Our concept allows a differentiation between volume-related effects like van der Waals interactions and surface-related effects like the interaction of a ligand with a solvent mixture. A comprehensive interpretation of classification results obtained with different good solvents and poor solvents enables to deduce a general strategy for the demanding determination of HSP for small colloids. Our work makes an important contribution to the design of an appropriate colloidal postprocessing which is applicable to larger quantities. © 2015 American Chemical Society.
view abstract doi: 10.1021/jp508746s 2015 • 205 CO oxidation as a test reaction for strong metal-support interaction in nanostructured Pd/FeO xpowder catalysts
Kast, P. and Friedrich, M. and Teschner, D. and Girgsdies, F. and Lunkenbein, T. and D'Alnoncourt, R.N. and Behrens, M. and Schlögl, R.
Applied Catalysis A: General 502 8-17 (2015)A series of differently loaded palladium-iron catalysts was prepared by a controlled co-precipitation method of the nitrate precursors, in order to ensure homogeneous Pd particle size-distribution. After characterization of the pre-catalysts by various techniques, different controlled reduction conditions were applied to investigate the interactions within the Pd-iron system, containing reversible and irreversible processes like phase transformations, SMSI, sintering and alloying. Strong indications for the reversible surface decoration of the Pd nanoparticles with iron oxide species via strong metal-support interaction were found by the combined results of DRIFTS, CO-chemisorption, TEM and XPS measurements. This SMSI state was found to be unstable. It was observed independent of bulk phase or palladium particle size. Catalytic CO-oxidation was found to be a suitable test reaction for the study of the phenomenon: higher activity as well as oxidative deactivation of the SMSI state was observed by investigating the light-off behavior in repeated, temperature-programmed cycles as well as by isothermal measurements. The instability was found to be higher in case of higher Pd dispersion. In addition, bulk properties of the Pd-Fe system, like alloying, were investigated by detailed XRD measurements. © 2015 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.apcata.2015.04.010 2015 • 204 Combinatorial Development of Fe-Co-Nb Thin Film Magnetic Nanocomposites
Alexandrakis, V. and Wallisch, W. and Hamann, S. and Varvaro, G. and Fidler, J. and Ludwig, Al.
ACS Combinatorial Science 17 698-703 (2015)A Fe-Co-Nb thin film materials library was deposited by combinatorial magnetron sputtering and investigated by high-throughput methods to identify new noncubic ferromagnetic phases, indicating that combinatorial experimentation is an efficient method to discover new ferromagnetic phases adequate for permanent magnet applications. Structural analysis indicated the formation of a new magnetic ternary compound (Fe,Co)3Nb with a hexagonal crystal structure (C36) embedded in an FeCo-based matrix. This nanocomposite exhibits characteristics of a two-phase ferromagnetic system, the so-called hard-soft nanocomposites, indicating that the new phase (Fe,Co)3Nb is ferromagnetic. Magnetic hysteresis loops at various angles revealed that the magnetization reversal process is governed by a domain wall pinning mechanism. © 2015 American Chemical Society.
view abstract doi: 10.1021/acscombsci.5b00116 2015 • 203 Coupled three dimensional DEM-CFD simulation of a lime shaft kiln-Calcination, particle movement and gas phase flow field
Krause, B. and Liedmann, B. and Wiese, J. and Wirtz, S. and Scherer, V.
Chemical Engineering Science 134 834-849 (2015)In lime shaft kilns the limestone is heated in counterflow with the flue gas from multiple burners, commonly fired by fossil or alternative fuels. After preheating, the limestone enters the calcination zone with gas temperatures above approximately 900. °C. To achieve high thermal efficiencies and calcination degrees, a homogeneous gas flow through the packed bed is essential. Spatial pressure differences and energy sinks and sources resulting from the calcination process and the fuel combustion make it even more difficult to predict the actual three-dimensional temperature and flow distribution in the kiln. Furthermore the particle size distribution is important for the system design, because limestone with larger size needs significantly higher residence time in the calcination zone for full conversion. This work presents the application of a novel 3-dimensional particle-mechanics based, numerical tool on an industrial scale. The tool allows the simulation of a moving and reacting limestone bed in a shaft kiln coupled with the 3-dimensional CFD-simulation describing the interstitial gas phase. Convective heat transfer between gas phase and particles, radiative and contact heat transfer between particles as well as calcination reaction are accounted for. With this combined approach the calcination of the limestone bed can be simultaneously described on the system scale while resolving detailed thermo-chemical processes on the particle scale. © 2015 Published by Elsevier Ltd.
view abstract doi: 10.1016/j.ces.2015.06.002 2015 • 202 Design of Thermally Responsive Polymeric Hydrogels for Brackish Water Desalination: Effect of Architecture on Swelling, Deswelling, and Salt Rejection
Ali, W. and Gebert, B. and Hennecke, T. and Graf, K. and Ulbricht, M. and Gutmann, J.S.
ACS Applied Materials and Interfaces 7 15696-15706 (2015)In this work, we explore the ability of utilizing hydrogels synthesized from a temperature-sensitive polymer and a polyelectrolyte to desalinate salt water by means of reversible thermally induced absorption and desorption. Thus, the influence of the macromolecular architecture on the swelling/deswelling behavior for such hydrogels was investigated by tailor-made network structures. To this end, a series of chemically cross-linked polymeric hydrogels were synthesized via free radical-initiated copolymerization of sodium acrylate (SA) with the thermoresponsive comonomer N-isopropylacrylamide (NIPAAm) by realizing different structural types. In particular, two different polyNIPAAm macromonomers, either with one acrylate function at the chain end or with additional acrylate functions as side groups were synthesized by controlled polymerization and subsequent polymer-analogous reaction and then used as building blocks. The rheological behaviors of hydrogels and their estimated mesh sizes are discussed. The performance of the hydrogels in terms of swelling and deswelling in both deionized water (DI) and brackish water (2 g/L NaCl) was measured as a function of cross-linking degree and particle size. The salt content could be reduced by 23% in one cycle by using the best performing material. (Figure Presented). © 2015 American Chemical Society.
view abstract doi: 10.1021/acsami.5b03878 2015 • 201 Determination of small soot particles in the presence of large ones from time‑resolved laser‑induced incandescence
Cenker, E. and Bruneaux, G. and Dreier, T. and Schulz, C.
Applied Physics B: Lasers and Optics 118 169-183 (2015)A novel strategy for the analysis of time-resolved laser-induced incandescence (TiRe-LII), called two-exponential reverse ftting (TERF), is introduced. The method is based on combined monoexponential fts to the LII signal decay at various delay times and approximates the particle-size distribution as a weighted combination of one large and one small monodisperse equivalent mean particle size without requiring assumption on the particle-size distribution. The effects of particle size, heat-up temperature, aggregate size, and pressure on the uncertainty of this method are evaluated using numerical experiments for lognormal and bimodal size distributions. TERF is applied to TiRe-LII measured in an atmospheric pressure laminar non-premixed ethylene/air fame at various heights above burner. The results are compared to transmission electron microscopy (TEM) measurements of thermophoretically sampled soot. The particle size of the large particle-size class agreed well for both methods. The size of the small particle-size class and the relative contribution did not agree which is attributed to missing information in the TEM results for very small particles. These limitations of TEM measurements are discussed and the effect of the exposure time of the sampling grid is evaluated. © Springer-Verlag Berlin Heidelberg 2014.
view abstract doi: 10.1007/s00340-014-5966-z 2015 • 200 Doping of inorganic materials in microreactors-preparation of Zn doped Fe3O4 nanoparticles
Simmons, M.D. and Jones, N. and Evans, D.J. and Wiles, C. and Watts, P. and Salamon, S. and Escobar Castillo, M. and Wende, H. and Lupascu, D.C. and Francesconi, M.G.
Lab on a Chip - Miniaturisation for Chemistry and Biology 15 3154-3162 (2015)Microreactor systems are now used more and more for the continuous production of metal nanoparticles and metal oxide nanoparticles owing to the controllability of the particle size, an important property in many applications. Here, for the first time, we used microreactors to prepare metal oxide nanoparticles with controlled and varying metal stoichiometry. We prepared and characterised Zn-substituted Fe3O4 nanoparticles with linear increase of Zn content (ZnxFe3-xO4 with 0 ≤ x ≤ 0.48), which causes linear increases in properties such as the saturation magnetization, relative to pure Fe3O4. The methodology is simple and low cost and has great potential to be adapted to the targeted doping of a vast array of other inorganic materials, allowing greater control on the chemical stoichiometry for nanoparticles prepared in microreactors. © 2015 The Royal Society of Chemistry.
view abstract doi: 10.1039/c5lc00287g 2015 • 199 Drying of iron chloride solutions: Laser heating of levitated single particles
Schiemann, M. and Baer, S. and Esen, C. and Ostendorf, A.
Chemical Engineering and Technology 38 947-951 (2015)Iron chloride solutions are a waste product from the steel industry, which has to be recovered by the so-called spray roasting process. As this process is a complex sequence of different steps, the drying process of the droplets was separated to get deeper insight into the particle formation process from aqueous iron chloride solutions. Experiments were carried out on single droplets in an acoustic levitator. A CO<inf>2</inf> laser was used as heat source for the drying process. Particles with different shapes were generated by various concentrations of FeCl<inf>2</inf> and laser power. The characteristic time scales and particle size evolution are compared with literature data. To get deeper insight into the particle formation process from aqueous iron chloride solutions, experiments were performed with single droplets in an acoustic levitator. A CO<inf>2</inf> laser served as heat source for drying. Varying FeCl<inf>2</inf> concentrations and laser power allowed for generating particles with different shapes. Time scales and particle size evolution were compared to literature data. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/ceat.201400594 2015 • 198 Dustiness and deagglomeration testing: Interlaboratory comparison of systems for nanoparticle powders
Ding, Y. and Stahlmecke, B. and Jiménez, A.S. and Tuinman, I.L. and Kaminski, H. and Kuhlbusch, T.A.J. and Van Tongeren, M. and Riediker, M.
Aerosol Science and Technology 49 1222-1231 (2015)Different types of aerosolization and deagglomeration testing systems exist for studying the properties of nanomaterial powders and their aerosols. However, results are dependent on the specific methods used. In order to have well-characterized aerosols, we require a better understanding of how system parameters and testing conditions influence the properties of the aerosols generated. In the present study, four experimental setups delivering different aerosolization energies were used to test the resultant aerosols of two distinct nanomaterials (hydrophobic and hydrophilic TiO2). The reproducibility of results within each system was good. However, the number concentrations and size distributions of the aerosols created varied across the four systems; for number concentrations, e.g., from 103 to 106 #/cm3. Moreover, distinct differences were also observed between the two materials with different surface coatings. The article discusses how system characteristics and other pertinent conditions modify the test results. We propose using air velocity as a suitable proxy for estimating energy input levels in aerosolization systems. The information derived from this work will be especially useful for establishing standard operating procedures for testing nanopowders, as well as for estimating their release rates under different energy input conditions, which is relevant for occupational exposure. © 2015 American Association for Aerosol Research.
view abstract doi: 10.1080/02786826.2015.1114999 2015 • 197 Effects of Feedstock Decomposition and Evaporation on the Composition of Suspension Plasma-Sprayed Coatings
Mauer, G. and Schlegel, N. and Guignard, A. and Vaßen, R. and Guillon, O.
Journal of Thermal Spray Technology 24 1187-1194 (2015)Emerging new applications and growing demands of plasma-sprayed coatings have initiated the development of new plasma spray processes. One of them is suspension plasma spraying (SPS). The use of liquid feedstock such as suspensions yields higher flexibility compared to the conventional atmospheric plasma spray processes as even submicron-to nano-sized particles can be processed. This allows achieving particular microstructural features, e.g., porous segmented or columnar-structured thermal barrier coatings. To exploit the potentials of such novel plasma spray processes, the plasma-feedstock interaction must be understood better. In this study, decomposition and evaporation of feedstock material during SPS were investigated, since particular difficulties can occur with respect to stoichiometry and phase composition of the deposits. Plasma conditions were analyzed by optical emission spectroscopy (OES). Experimental results are given, namely for gadolinium zirconate and for lanthanum strontium cobalt ferrite deposition. Moreover, the applied OES approach is validated by comparison with the simpler actinometry method. © 2015, ASM International.
view abstract doi: 10.1007/s11666-015-0250-2 2015 • 196 Enhanced Nucleation of Lysozyme Using Inorganic Silica Seed Particles of Different Sizes
Weichsel, U. and Segets, D. and Janeke, S. and Peukert, W.
Crystal Growth and Design 15 3582-3593 (2015)In this work we investigate the impact of differently sized plain silica nanoparticles (NPs) between 10 and 200 nm on the crystallization of lysozyme (LSZ). In the first part of our work we investigate the electrostatic interactions between LSZ and NPs by zeta potential measurements and place special emphasis on the adsorption behavior of LSZ@SiO<inf>2</inf>. The determined adsorption isotherms - derived from UV-vis spectroscopy - indicate that with increasing particle size more LSZ is adsorbed per NP surface area probably due to a size-dependent surface chemistry and the variation of surface curvature. Second, seeded crystallization experiments both at the microliter and milliliter scale and thus close to a technically relevant scale were performed. A clearly extended crystallization window upon the addition of seed particles toward lower protein and salt concentrations was found. Moreover, induction times of crystal formation and crystallization times were considerably reduced. These effects were intensified with the addition of larger seed particles. In general, with the addition of silica seed particles, a shift of the final crystal size distribution to larger structures is observed. © 2015 American Chemical Society.
view abstract doi: 10.1021/cg501681g 2015 • 195 FIMOR: An efficient simulation for ZnO quantum dot ripening applied to the optimization of nanoparticle synthesis
Haderlein, M. and Segets, D. and Gröschel, M. and Pflug, L. and Leugering, G. and Peukert, W.
Chemical Engineering Journal 260 706-715 (2015)This work presents the application of a Fully Implicit Method for Ostwald Ripening (FIMOR) for simulating the ripening of ZnO quantum dots (QDs). Its stable numerics allow FIMOR to employ the full exponential term of the Gibbs-Thomson equation which significantly outperforms the common Taylor-approximation at typical QD sizes below 10. nm. The implementation is consistent with experimental data for temperatures between 10 and 50. °C and the computational effort is reduced by a factor of 100-1000 compared to previous approaches. This reduced the simulation time on a standard PC from several hours to a few minutes. In the second part, we demonstrate the high potential and accuracy of FIMOR by its application to several challenging studies. First, we compare numeric results obtained for ripening of ZnO QDs exposed to temperature ramps with experimental data. The deviation between simulation and experiment in the mean volume weighted particle size was as small as 5%. Second, a map for the process parameter space spanned by ripening time and temperature is created based on a large number (>50) of FIMOR runs. From this map appropriate process parameters to adjust a desired dispersity are easily deduced. Further data analysis reveals in agreement with literature findings that the particle size distribution converges towards a self-preserving stable shape. Equations describing the time dependent particle size distribution with high accuracy are presented. Finally, we realized the transfer from low volume batch experiments to continuous QD processing. We modeled the continuous ZnO synthesis in a fully automated microreaction plant and found an excellent agreement between the numeric prediction and the experimental results by considering the residence time distribution. © 2014 Elsevier B.V.
view abstract doi: 10.1016/j.cej.2014.09.040 2015 • 194 From in situ characterization to process control of quantum dot systems
Segets, D. and Peukert, W.
Procedia Engineering 102 575-581 (2015)Quantum confined semiconductor nanoparticles (quantum dots, QDs) are promising candidates for various applications in emerging fields like electronics, solar cells, sensors and diagnostics. However, a larger scale production of QDs at high product quality is still missing. One of the key requirements to address this issue in the near future was identified to be a fast and in situ applicable characterization method. Suitable characterization requires knowledge on the full shape of the particle size distributions (PSDs) under investigation. Thus, determination of a mean particle size together with the width of the PSD is not sufficient. In the following, a method will be presented that allows the derivation of arbitrary shaped PSDs for QDs with direct band gap based on their optical absorbance spectra. After validation of the technique by means of ZnO nanoparticles the transfer of the concept to other QD materials like PbS and PbSe will be proven. Therefore we will extend our methodology and show how our approach can be used to derive spectral properties like the size dependent band gap energy. This is realized by proper calibration of the calculation results against PSDs determined by an independent analysis technique like transmission electron microscopy (TEM). © 2015 The Authors.
view abstract doi: 10.1016/j.proeng.2015.01.129 2015 • 193 Heat transfer in indirect heated rotary drums filled with monodisperse spheres: Comparison of experiments with DEM simulations
Komossa, H. and Wirtz, S. and Scherer, V. and Herz, F. and Specht, E.
Powder Technology 286 722-731 (2015)Numerical simulations with the discrete element method (DEM) and corresponding experimental investigations were carried out to understand and to quantify the heat transfer in indirect heated rotating drums. Monodisperse glass spheres (diameter 2. mm) were used and the bulk movement was kept within the rolling motion mode (rotational speed between 1 and 9. rpm). The focus is on the heat transfer between the covered wall and the particles in contact with this wall, as well as between the particles on the free bed surface and the adjacent fluid. Radiative heat transfer has been neglected due to the low maximum temperature within the system (474. K). Effective heat transfer coefficients for the heat fluxes mentioned were derived from the DEM simulations, considering the actual particle velocities on the free bed surface and on the wall.The particle movement and the heat transfer resulting from the simulations show good agreement with the experiments in general and thus allow the calculation of the effective heat transfer coefficients for the range of parameters considered in the current study. © 2015 Published by Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2015.07.022 2015 • 192 High-Speed GaN/GaInN Nanowire Array Light-Emitting Diode on Silicon(111)
Koester, R. and Sager, D. and Quitsch, W.-A. and Pfingsten, O. and Poloczek, A. and Blumenthal, S. and Keller, G. and Prost, W. and Bacher, G. and Tegude, F.-J.
Nano Letters 15 2318-2323 (2015)(Graph Presented). The high speed on-off performance of GaN-based light-emitting diodes (LEDs) grown in c-plane direction is limited by long carrier lifetimes caused by spontaneous and piezoelectric polarization. This work demonstrates that this limitation can be overcome by m-planar core-shell InGaN/GaN nanowire LEDs grown on Si(111). Time-resolved electroluminescence studies exhibit 90-10% rise- and fall-times of about 220 ps under GHz electrical excitation. The data underline the potential of these devices for optical data communication in polymer fibers and free space. © 2015 American Chemical Society.
view abstract doi: 10.1021/nl504447j 2015 • 191 Impact of ambient pressure on titania nanoparticle formation during spray-flame synthesis
Hardt, S. and Wlokas, I. and Schulz, C. and Wiggers, H.
Journal of Nanoscience and Nanotechnology 15 9449-9456 (2015)Nanocrystalline titania was synthesized via liquid-fed spray-flame synthesis in a hermetically closed system at various pressures. Titanium tetraisopropoxide dissolved in isopropanol was used as precursor. The size, crystal structure, degree of agglomeration, morphology and the band gap of the as-prepared particles were investigated ex situ by nitrogen adsorption, transmission electron microscopy, X-ray diffraction, and UV-VIS absorption spectroscopy. In comparison to synthesis at atmospheric pressure it was found that decreasing pressure has a significant influence on the particle size distribution leading to smaller particles with reduced geometric standard deviation while particle morphology and crystal structure are not affected. Computational fluid dynamics simulations support the experimental findings also indicating a significant decrease in particle size at reduced pressure. Although it is well known that decreasing pressure leads to smaller particle sizes, it is (to our knowledge) the first time that this relation was investigated for spray-flame synthesis. Copyright © 2015 American Scientific Publishers All rights reserved.
view abstract doi: 10.1166/jnn.2015.10607 2015 • 190 Impact of bacterial endotoxin on the structure of DMPC membranes
Nagel, M. and Brauckmann, S. and Moegle-Hofacker, F. and Effenberger-Neidnicht, K. and Hartmann, M. and De Groot, H. and Mayer, C.
Biochimica et Biophysica Acta - Biomembranes 1848 2271-2276 (2015)Abstract Bacterial lipopolysaccharides are believed to have a toxic effect on human cell membranes. In this study, the influence of a lipopolysaccharide (LPS) from Escherichia coli on the structure, the dynamics and the mechanical strength of phospholipid membranes are monitored by nuclear magnetic resonance spectroscopy (NMR) and by atomic force microscopy (AFM). Model membranes are formed from 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and are either prepared as multilamellar bulk samples or multilamellar vesicles. Field gradient NMR data directly prove the rapid integration of LPS into DMPC membranes. Solid state NMR experiments primarily detect decreasing molecular order parameters with increasing LPS content. This is accompanied by a mechanical softening of the membrane bilayers as is shown by AFM indentation measurements. Altogether, the data prove that lipopolysaccharide molecules quickly insert into phospholipid bilayers, increase membrane fluctuation amplitudes and significantly weaken their mechanical stiffness. © 2015 Published by Elsevier B.V.
view abstract doi: 10.1016/j.bbamem.2015.06.008 2015 • 189 In Situ Study on the Evolution of Multimodal Particle Size Distributions of ZnO Quantum Dots: Some General Rules for the Occurrence of Multimodalities
Schindler, T. and Walter, J. and Peukert, W. and Segets, D. and Unruh, T.
Journal of Physical Chemistry B 119 15370-15380 (2015)Properties of small semiconductor nanoparticles (NPs) are strongly governed by their size. Precise characterization is a key requirement for tailored dispersities and thus for high-quality devices. Results of a careful analysis of particle size distributions (PSDs) of ZnO are presented combining advantages of UV/vis absorption spectroscopy, analytical ultracentrifugation, and small-angle X-ray scattering (SAXS). Our study reveals that careful cross-validation of these different methods is mandatory to end up with reliable resolution. PSDs of ZnO NPs are multimodal on a size range of 2-8 nm, a finding that is not yet sufficiently addressed. In the second part of our work the evolution of PSDs was studied using in situ SAXS. General principles for the appearance of multimodalities covering a temperature range between 15 and 45 °C were found which are solely determined by the aging state indicated by the size of the medium-sized fraction. Whenever this fraction exceeds a critical diameter, a new multimodality is identified, independent of the particular time-temperature combination. A fraction of larger particles aggregates first before a fraction of smaller particles is detected. Fixed multimodalities have not yet been addressed adequately and could only be evidenced due to careful size analysis. © 2015 American Chemical Society.
view abstract doi: 10.1021/acs.jpcb.5b08005 2015 • 188 Influence of carbon content, particle size, and partial manganese substitution on the electrochemical performance of LiFe xMn 1-xPO 4/carbon composites
Hamid, N.A. and Wennig, S. and Heinzel, A. and Schulz, C. and Wiggers, H.
Ionics 21 1857-1866 (2015)LiFePO<inf>4</inf>/C and LiFe<inf>x</inf>Mn<inf>1-x</inf>PO<inf>4</inf>/C (x = 0.7) nanocomposites were successfully synthesized via scalable spray-flame synthesis followed by solid-state reaction. A solution of iron (III) acetylacetonate and tributyl phosphate in toluene was used to produce amorphous, nanosized FePO<inf>4</inf>⋅H<inf>2</inf>O in a spray-flame reactor which was then milled with Li<inf>2</inf>CO<inf>3</inf> and glucose to produce a LiFePO<inf>4</inf>/C composite material in a solid-state reaction. The influence of calcination temperature and carbon content on the properties of the resulting material was investigated using specific surface area measurements (BET), X-ray diffraction (XRD), electron microscopy, and electrochemical characterization. The impact of manganese addition on the electrochemical behavior was analyzed using cyclic voltammetry (CV) and constant-current (CC) measurements. XRD shows that the combination of gas-phase synthesis and subsequent solid-state reaction yields highly pure LiFePO<inf>4</inf>/C. BET measurement revealed that the particle size of LiFePO<inf>4</inf> in the composite depends on the amount of glucose. A discharge capacity of more than 140 mAh/g at C/20 is achieved for LiFePO<inf>4</inf>/C with a carbon content of 6 wt%. This material supports high charge as well as discharge rates delivering more than 60 mAh/g at 16 C and sustains good cycle stability providing 115 mAh/g at 1 C. The energy density of the olivine increases about 10 % by substituting 30 mol% of iron by manganese while preserving the electrochemical performance of pure LiFePO<inf>4</inf>/C. © 2015, Springer-Verlag Berlin Heidelberg.
view abstract doi: 10.1007/s11581-015-1366-6 2015 • 187 Inversion of electrical mobility measurements using bipolar or unipolar chargers for the arbitrary distribution of channels
Domat, M. and Kruis, F.E. and Azong-Wara, N.L. and Fernandez-Diaz, J.M.
Particuology 20 114-123 (2015)The inversion of the particle size distribution from electrical mobility measurements is analyzed. Three different methods are adapted for a dot-matrix approach to the problem, especially for non-square or singular matrices, and applied to electrical mobility measurements from fixed or scanning voltages. Multiply charged particles, diffusion losses, arbitrary voltage steps and noise were considered, which results in non-adjoining and overlapping transfer functions. The individual contribution of the transfer functions in each size interval was geometrically estimated, which requires only its characteristic mobilities. The methodology is applied to mobility measurements from particles charged with unipolar and bipolar chargers. However, the method can be extrapolated to any charging method with a defined charge distribution, and retrieval of the singly charged particle distribution and mean charge from a tandem differential mobility analysis configuration was successfully demonstrated. © 2014 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy ofSciences. Published by Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.partic.2014.08.007 2015 • 186 Investigation of the size-property relationship in CuInS2 quantum dots
Akdas, T. and Walter, J. and Segets, D. and Distaso, M. and Winter, B. and Birajdar, B. and Spiecker, E. and Peukert, W.
Nanoscale 7 18105-18118 (2015)In this work we investigated fundamental properties of CuInS2 quantum dots in dependence of the particle size distribution (PSD). Size-selective precipitation (SSP) with acetone as poor solvent was performed as an adequate post-processing step. Our results provide deep insight into the correlation between particle size and various optical characteristics as bandgap energy, absorption and emission features and the broadness of the emission signal. These structure-property relationships are only achieved due to the unique combination of different analytical techniques. Our study reveals that the removal of 10 wt% of smallest particles from the feed results in an enhancement of the emission signal. This improvement is ascribed to a decreased quenching of the emission in larger particles. Our results reveal the impact of PSDs on the properties and the performance of an ensemble of multicomponent QDs and anticipate the high potential of controlling PSDs by well-developed post-processing. © 2015 The Royal Society of Chemistry.
view abstract doi: 10.1039/c5nr04291g 2015 • 185 Iron-doped nickel oxide nanocrystals as highly efficient electrocatalysts for alkaline water splitting
Fominykh, K. and Chernev, P. and Zaharieva, I. and Sicklinger, J. and Stefanic, G. and Döblinger, M. and Müller, A. and Pokharel, A. and Böcklein, S. and Scheu, C. and Bein, T. and Fattakhova-Rohlfing, D.
ACS Nano 9 5180-5188 (2015)Efficient electrochemical water splitting to hydrogen and oxygen is considered a promising technology to overcome our dependency on fossil fuels. Searching for novel catalytic materials for electrochemical oxygen generation is essential for improving the total efficiency of water splitting processes. We report the synthesis, structural characterization, and electrochemical performance in the oxygen evolution reaction of Fe-doped NiO nanocrystals. The facile solvothermal synthesis in tert-butanol leads to the formation of ultrasmall crystalline and highly dispersible Fe<inf>x</inf>Ni<inf>1-x</inf>O nanoparticles with dopant concentrations of up to 20%. The increase in Fe content is accompanied by a decrease in particle size, resulting in nonagglomerated nanocrystals of 1.5-3.8 nm in size. The Fe content and composition of the nanoparticles are determined by X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy measurements, while Mössbauer and extended X-ray absorption fine structure analyses reveal a substitutional incorporation of Fe(III) into the NiO rock salt structure. The excellent dispersibility of the nanoparticles in ethanol allows for the preparation of homogeneous ca. 8 nm thin films with a smooth surface on various substrates. The turnover frequencies (TOF) of these films could be precisely calculated using a quartz crystal microbalance. Fe<inf>0.1</inf>Ni<inf>0.9</inf>O was found to have the highest electrocatalytic water oxidation activity in basic media with a TOF of 1.9 s-1 at the overpotential of 300 mV. The current density of 10 mA cm-2 is reached at an overpotential of 297 mV with a Tafel slope of 37 mV dec-1. The extremely high catalytic activity, facile preparation, and low cost of the single crystalline Fe<inf>x</inf>Ni<inf>1-x</inf>O nanoparticles make them very promising catalysts for the oxygen evolution reaction. © 2015 American Chemical Society.
view abstract doi: 10.1021/acsnano.5b00520 2015 • 184 Kinetics of deactivation on Cu/ZnO/Al 2O 3methanol synthesis catalysts
Fichtl, M.B. and Schlereth, D. and Jacobsen, N. and Kasatkin, I. and Schumann, J. and Behrens, M. and Schlögl, R. and Hinrichsen, O.
Applied Catalysis A: General 502 262-270 (2015)Deactivation behavior is an important topic in catalyst development. In case of methanol synthesis the conventional Cu/ZnO/Al<inf>2</inf>O<inf>3</inf> system is commonly known to be prone to sintering, however, information about the structural development during deactivation or the sintering mechanism(s) are scarce. We present a systematic deactivation study on three different Cu/ZnO/Al<inf>2</inf>O<inf>3</inf> catalysts which are aged under constant conditions and periodically analyzed using kinetic measurements and N<inf>2</inf>O chemisorption. A power law model for the catalyst activity with time on stream is derived. Furthermore it is found, that the presence of water provokes a steep loss in active surface area and specific activity. Also, the TEM particle size distributions generated during the aging treatment are evaluated and discussed. © 2015 Elsevier Ltd. All rights reserved.
view abstract doi: 10.1016/j.apcata.2015.06.014 2015 • 183 Measurement of drag coefficients of non-spherical particles with a camera-based method
Krueger, B. and Wirtz, S. and Scherer, V.
Powder Technology 278 157-170 (2015)The current paper presents a novel experimental set-up which allows the automated determination of the drag coefficients of relatively large particles with complex shape. Typical examples of such types of particles are waste derived fuel (RDF) particles which are non-spherical and have a size up to a few centimeters. In contrast to conventional fossil fuel particles, where the particles may be considered as material points during the calculation of particle tracks in a reacting flow field, the spatial extent of RDF-particles and their lack of sphericity lead to pronounced self-induced movement and associated variations in the drag-coefficients.The experiments are based on a drop shaft equipped with two digital cameras. This allows to obtain time resolved stereo image sequences from which the settling velocity of particles, the self-induced velocity fluctuations and the corresponding drag and lift coefficients can be derived. As the system is automated, a large number of particles can be examined and statistical information on the distribution of drag coefficients can be obtained.In this publication, the methodology of these drop shaft measurements and their evaluation will be presented. Additionally drag coefficients of isometric spherical and non-spherical particle geometries (spheres, cubes, square plates and circular disks) were measured and compared with known correlations for drag coefficients. Probability density functions for the properties of typical RDF particles will be presented to highlight the potential of the new set-up. © 2015 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2015.03.024 2015 • 182 Measurements of nanoscale TiO2 and Al2O3 in industrial workplace environments – Methodology and results
Kaminski, H. and Beyer, M. and Fissan, H. and Asbach, C. and Kuhlbusch, T.A.J.
Aerosol and Air Quality Research 15 129-141 (2015)The possible release of engineered nanomaterials was investigated based on a previously developed but now refined methodology. Data from altogether eight industrial work areas in production plants of nanostructured TiO2 and Al2O3 particles were obtained and used to test the methodology and to derive a first assessment of possible exposure of workers. Particle size distributions were determined in work area environments with concurrent measurements at a comparison site. Data from the comparison site were used to estimate the particle background level in the work area and distinguish it from potentially released nanomaterial. The analysis is based on the comparison of time resolved data from the work area and the comparison site as well as data determined during periods with and without work activities in the work area. The data analysis method introduced delivers size-resolved information on the potential nanoparticle exposure of workers. A significant release of particles in the size range 100–562 nm was observed in the work area of bagging aluminum oxide and is stemming from damaging or overfilling of bags, and the necessary activities during the cleaning of the work area. The maximum particle diameter of these particles was around 340 nm. At all other investigated locations no significant releases of particles in the size range 100–562 nm were determined. Also, no significant release of particles < 100 nm was observed in all work areas. The average PM10 exposure during the work activities varied from 48 to 1,330 µg/m3 in the different work areas. The maximum concentrations of aluminum were 118 µg/m3 and 58 µg/m3 for PM10 and PM1, respectively, during the bagging of Al2O3 in small bags. In comparison, the maximum concentrations of titanium were 550 µg/m3 and 434 µg/m3 for PM10 and PM1, respectively, during the bagging of TiO2 and indicate a significant release of coarser particles. © Taiwan Association for Aerosol Research.
view abstract doi: 10.4209/aaqr.2014.03.0065 2015 • 181 Mesoporous Silica Supported Au and AuCu Nanoparticles for Surface Plasmon Driven Glycerol Oxidation
Schünemann, S. and Dodekatos, G. and Tüysüz, H.
Chemistry of Materials 27 7743-7750 (2015)Herein, we report for the first time the visible-light-assisted rate enhancement for glycerol oxidation using direct plasmonic photocatalysis. Au nanoparticles were loaded on various mesoporous SiO2 supports, and the catalytic performance was investigated with and without visible-light illumination. Monodispersed mesoporous silica spheres loaded with Au nanoparticles demonstrated a superior photoassisted catalytic rate enhancement compared to Au loaded ordered mesoporous silica (SBA-15, KIT-6, and MCM-41). The enhancement is attributed to the particle size of the Au nanoparticles and better light interaction resulting from the small SiO2 domains. Au loaded monodispersed mesoporous silica spheres exhibit a constant and remarkably small particle diameter of 2 nm at Au loadings of up to 15 wt % as a result of the support's small domain size and efficient pore confinement. The performance of the Au catalyst could be further improved by preparing bimetallic AuCu nanoparticles. Synergistic effects between Au and Cu improved the glycerol conversion by a factor of 2.5 and the dihydroxyacetone selectivity from 80% to 90% compared to monometallic Au catalysts. © 2015 American Chemical Society.
view abstract doi: 10.1021/acs.chemmater.5b03520 2015 • 180 Microstructure refinement for high modulus in-situ metal matrix composite steels via controlled solidification of the system Fe-TiB 2
Springer, H. and Aparicio Fernandez, R. and Duarte, M.J. and Kostka, A. and Raabe, D.
Acta Materialia 96 47-56 (2015)Microstructures of Fe-TiB<inf>2</inf> metal-matrix-composites formed in-situ from Fe-Ti-B melts were investigated for hypo- and hyper-eutectic concentrations down to atomic-scale resolution. Special emphasis is laid on the influence of the solidification rate on particle size, morphology and distribution as well as their relation to mechanical properties. Innovative routes for the cost-effective production of stiff and ductile high modulus steels for lightweight structural applications are discussed, focusing on hyper-eutectic compositions due to their high stiffness/density ratio: firstly, very slow cooling allows the primary particles floating to the top of the cast, from which they can either be easily removed for retaining bulk material containing only fine-dispersed eutectic particles, or be kept and utilised as a wear resistant surface. Secondly, annealing of amorphous matrix material obtained from very fast solidification leads to fine dispersed nano-scaled precipitation of TiB<inf>2</inf> particles. © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
view abstract doi: 10.1016/j.actamat.2015.06.017 2015 • 179 Mobility size and mass of nascent soot particles in a benchmark premixed ethylene flame
Camacho, J. and Liu, C. and Gu, C. and Lin, H. and Huang, Z. and Tang, Q. and You, X. and Saggese, C. and Li, Y. and Jung, H. and Deng, L. and Wlokas, I. and Wang, H.
Combustion and Flame 162 3810-3822 (2015)The burner stabilized stagnation flame technique coupled with micro-orifice probe sampling and mobility sizing has evolved into a useful tool for examining the evolution of the particle size distribution of nascent soot in laminar premixed flames. Several key aspects of this technique are examined through a multi-university collaborative study that involves both experimental measurement and computational modeling. Key issues examined include (a) data reproducibility and facility effects using four burners of different sizes and makers over three different facilities, (b) the mobility diameter and particle mass relationship, and (c) the degree to which the finite orifice flow rate affects the validity of the boundary condition in a pseudo one dimensional stagnation flow flame formulation. The results indicate that different burners across facilities yield nearly identical results after special attention is paid to a range of experimental details, including a proper selection of the sample dilution ratio and quantification of the experimental flame boundary conditions. The mobility size and mass relationship probed by tandem mass and mobility measurement shows that nascent soot with mobility diameter as small as 15 nm can deviate drastically from the spherical shape. Various non-spherical morphology models using a mass density value of 1.5 g/cm3 can reconcile this discrepancy in nascent soot mass. Lastly, two-dimensional axisymmetric simulations of the experimental flame with and without the sample orifice flow reveal several problems of the pseudo one-dimensional stagnation flow flame approximation. The impact of the orifice flow on the flame and soot sampled, although small, is not negligible. Specific suggestions are provided as to how to treat the non-ideality of the experimental setup in experiment and model comparisons. © 2015 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
view abstract doi: 10.1016/j.combustflame.2015.07.018 2015 • 178 Nano- And microlenses as concepts for enhanced performance of solar cells
Schmid, M. and Manley, P.
Journal of Photonics for Energy 5 (2015)Both metallic nanoparticles exhibiting plasmonic effects and dielectric nanoparticles coupling the light into resonant modes have shown successful applications to photovoltaics. On a larger scale, microconcentrator optics promise to enhance solar cell efficiency and to reduce material consumption. Here, we want to create a link between the concentrators on the nano- and on the microscale. From metallic nanospheres, we turn to dielectric ones and then look at increasing radii to approach the microscale. The lenses are investigated with respect to their interaction with light using three-dimensional simulations with the finite-element method. Resulting maps of local electric field distributions reveal the focusing behavior of the dielectric spheres. For larger lens sizes, ray tracing calculations, which give ray distributions in agreement with electric field intensities, can be applied. Calculations of back focal lengths in geometrical optics coincide with ray tracing results and allow insight into how the focal length can be tuned as a function of particle size, substrate refractive index, and the shape of the microlens. Despite the similarities we find for the nano- and the microlenses, integration into solar cells needs to be carefully adjusted, depending on the goals of material saving, concentration level, focal distance, and lens size. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE).
view abstract doi: 10.1117/1.JPE.5.057003 2015 • 177 New approaches to nanoparticle sample fabrication for atom probe tomography
Felfer, P. and Li, T. and Eder, K. and Galinski, H. and Magyar, A.P. and Bell, D.C. and Smith, G.D.W. and Kruse, N. and Ringer, S.P. and Cairney, J.M.
Ultramicroscopy 159 413-419 (2015)Due to their unique properties, nano-sized materials such as nanoparticles and nanowires are receiving considerable attention. However, little data is available about their chemical makeup at the atomic scale, especially in three dimensions (3D). Atom probe tomography is able to answer many important questions about these materials if the challenge of producing a suitable sample can be overcome. In order to achieve this, the nanomaterial needs to be positioned within the end of a tip and fixed there so the sample possesses sufficient structural integrity for analysis. Here we provide a detailed description of various techniques that have been used to position nanoparticles on substrates for atom probe analysis. In some of the approaches, this is combined with deposition techniques to incorporate the particles into a solid matrix, and focused ion beam processing is then used to fabricate atom probe samples from this composite. Using these approaches, data has been achieved from 10-20 nm core-shell nanoparticles that were extracted directly from suspension (i.e. with no chemical modification) with a resolution of better than ±1 nm. © 2015 Elsevier B.V..
view abstract doi: 10.1016/j.ultramic.2015.04.014 2015 • 176 On the mechanism of nanoparticle formation in a flame doped by iron pentacarbonyl
Poliak, M. and Fomin, A. and Tsionsky, V. and Cheskis, S. and Wlokas, I. and Rahinov, I.
Physical Chemistry Chemical Physics 17 680-685 (2015)In this work we have investigated the mechanism of nanoparticle synthesis in a low pressure, premixed, laminar flat flame of CH4-O2, doped with iron pentacarbonyl using a combined quartz-crystal-microbalance-particle-mass-spectrometry apparatus. We have unambiguously demonstrated that the formation of nanoparticles in iron pentacarbonyl-doped flames occurs very early, in close proximity to the burner surface, prior to the flame front. This early rise of nanoparticle mass concentration is followed by a sharp drop in nanoparticle concentration at the high temperature flame front. This "prompt" nanoparticle generation is consistent with kinetic models describing iron cluster formation. The observation of this phenomenon in a quasi-one-dimensional premixed flat flame strengthens our previous findings and points out that the "prompt" nanoparticle formation is a general phenomenon, not limited to diffusion flames. It presents a challenge and a trigger for further development of the existing mechanisms for gas phase synthesis of iron oxide particles in flames. This journal is © the Owner Societies 2015.
view abstract doi: 10.1039/c4cp04454a 2015 • 175 Reversible or Not? Distinguishing Agglomeration and Aggregation at the Nanoscale
Sokolov, S.V. and Tschulik, K. and Batchelor-McAuley, C. and Jurkschat, K. and Compton, R.G.
Analytical Chemistry 87 10033-10039 (2015)Nanoparticles are prone to clustering either via aggregation (irreversible) or agglomeration (reversible) processes. It is exceedingly difficult to distinguish the two via conventional techniques such as dynamic light scattering (DLS), nanoparticle tracking analysis (NTA), or electron microscopy imaging (scanning electron microscopy (SEM), transmission electron microscopy (TEM)) as such techniques only generally confirm the presence of large particle clusters. Herein we develop a joint approach to tackle the issue of distinguishing between nanoparticle aggregation vs agglomeration by characterizing a colloidal system of Ag NPs using DLS, NTA, SEM imaging and the electrochemical nanoimpacts technique. In contrast to the conventional techniques which all reveal the presence of large clusters of particles, electrochemical nanoimpacts provide information regarding individual nanoparticles in the solution phase and reveal the presence of small nanoparticles (<30 nm) even in high ionic strength (above 0.5 M KCl) and allow a more complete analysis. The detection of small nanoparticles in high ionic strength media evidence the clustering to be a reversible process. As a result it is concluded that agglomeration rather than irreversible aggregation takes place. This observation is of general importance for all colloids as it provides a feasible analysis technique for a wide range of systems with an ability to distinguish subtly different processes. © 2015 American Chemical Society.
view abstract doi: 10.1021/acs.analchem.5b02639 2015 • 174 Self-assembly of smallest magnetic particles
Taheri, S.M. and Michaelis, M. and Friedrich, T. and Förster, B. and Drechsler, M. and Römer, F.M. and Bösecke, P. and Narayanan, T. and Weber, B. and Rehberg, I. and Rosenfeldt, S. and Förster, S.
Proceedings of the National Academy of Sciences of the United States of America 112 14484-14489 (2015)The assembly of tiny magnetic particles in external magnetic fields is important for many applications ranging from data storage to medical technologies. The development of ever smaller magnetic structures is restricted by a size limit, where the particles are just barely magnetic. For such particles we report the discovery of a kind of solution assembly hitherto unobserved, to our knowledge. The fact that the assembly occurs in solution is very relevant for applications, where magnetic nanoparticles are either solutionprocessed or are used in liquid biological environments. Induced by an external magnetic field, nanocubes spontaneously assemble into 1D chains, 2D monolayer sheets, and large 3D cuboids with almost perfect internal ordering. The self-assembly of the nanocubes can be elucidated considering the dipole-dipole interaction of small superparamagnetic particles. Complex 3D geometrical arrangements of the nanodipoles are obtained under the assumption that the orientation of magnetization is freely adjustable within the superlattice and tends to minimize the binding energy. On that basis the magnetic moment of the cuboids can be explained.
view abstract doi: 10.1073/pnas.1511443112 2015 • 173 Sensitivity analysis for soot particle size imaging with laser-induced incandescence at high pressure
Cenker, E. and Bruneaux, G. and Dreier, T. and Schulz, C.
Applied Physics B: Lasers and Optics 119 745-763 (2015)Soot particle sizes can be determined from time-resolved laser-induced incandescence (LII) in point measurements where full signal traces are detected. For instantaneous imaging, strategies are required that must cope with time-gated information and that rely on assumptions on the local boundary conditions. A model-based analysis is performed to identify the dependence of LII particle-size imaging on the assumed boundary conditions such as bath gas temperature, pressure, particle heat-up temperature, accommodation coefficients, and soot aggregate size. Various laser-fluence regimes and gas pressures are considered. For 60 bar, fluences that lead to particle heat-up temperatures of 3,400–3,900 K provided the lowest sensitivity on particle sizing. Effects of laser attenuation are evaluated. A combination of one detection gate starting at the signal peak and the other starting with 5 ns delay was found to provide the highest sensitivity at 60 bar. The optimum gate delays for different pressures are shown. The effects of timing jitter, polydispersity, and signal noise are investigated. Systematic errors in pyrometry imaging at 60 bar is evaluated. © 2015, Springer-Verlag Berlin Heidelberg.
view abstract doi: 10.1007/s00340-015-6009-0 2015 • 172 Simplified formulations with high drug loads for continuous twin-screw granulation
Meier, R. and Thommes, M. and Rasenack, N. and Krumme, M. and Moll, K.-P. and Kleinebudde, P.
International Journal of Pharmaceutics 496 12-23 (2015)As different batches of the same excipients will be intermixed during continuous processes, the traceability of batches is complicated. Simplified formulations may help to reduce problems related to batch intermixing and traceability. Twin-screw granulation with subsequent tableting was used to produce granules and tablets, containing drug, disintegrant and binder (binary and ternary mixtures), only. Drug loads up to 90% were achieved and five different disintegrants were screened for keeping their disintegration suitability after wetting. Granule size distributions were consistently mono-modal and narrow. Granule strength reached higher values, using ternary mixtures. Tablets containing croscarmellose-Na as disintegrant displayed tensile strengths up to 3.1 MPa and disintegration times from 400 to 466 s, resulting in the most robust disintegrant. Dissolution was overall complete and above 96% within 30 min. Na-starch glycolate offers tensile strengths up to 2.8 MPa at disintegration times from 25 s to 1031 s, providing the broadest application window, as it corresponds in some parts to different definitions of orodispersible tablets. Tablets containing micronized crospovidone are not suitable for immediate release, but showed possibilities to produce highly drug loaded, prolonged release tablets. Tablets and granules from simplified formulations offer great opportunities to improve continuous processes, present performances comparable to more complicated formulations and are able to correspond to requirements of the authorities. © 2015 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.ijpharm.2015.05.060 2015 • 171 Size control and supporting of palladium nanoparticles made by laser ablation in saline solution as a facile route to heterogeneous catalysts
Marzun, G. and Nakamura, J. and Zhang, X. and Barcikowski, S. and Wagener, P.
Applied Surface Science 348 75-84 (2015)In the literature many investigations on colloidal stability and size control of gold nanoparticles are shown but less for ligand-free palladium nanoparticles, which can be promising materials in various applications. Palladium nanoparticles are perspective materials for a manifold of energy application like photo- and electrocatalysis or hydrogen storage. For this purpose, size-controlled nanoparticles with clean surfaces and facile immobilization on catalyst supports are wanted. Laser ablation in saline solution yields ligand-free, charged colloidal palladium nanoparticles that are supported by titania and graphene nanosheets as model systems for photo- and electrocatalysis, respectively. By adjusting the ionic strength during laser ablation in liquid, it is possible to control stability and particle size without compromising subsequent nanoparticle adsorption of supporting materials. A quantitative deposition of nearly 100% yield with up to 18 wt% nanoparticle load was achieved. The average size of the laser-generated nanoparticles remains the same after immobilization on a support material, in contrast to other preparation methods of catalysts. The characterization by X-ray photoelectron spectroscopy reveals a redox reaction between the immobilized nanoparticles and the graphene support. © 2015 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.apsusc.2015.01.108 2015 • 170 Size matters: An experimental and computational study of the influence of particle size on the lattice energy of NaCl
Range, S. and Bernardes, C.E.S. and Simões, R.G. and Epple, M. and Da Piedade, M.E.M.
Journal of Physical Chemistry C 119 4387-4396 (2015)One of the most interesting features of nanomaterials is the change in properties that normally accompanies a decrease in particle size. Enthalpy of solution measurements in water, at 298 K, carried out with sodium chloride samples spanning a 500-fold particle size range (120 nm to 60 μm) evidenced the effect of the increase in surface area to volume ratio in the enthalpy of solution and cohesive energy of NaCl. The nanoscopic samples were prepared by a new malonic ester synthesis, which allowed the production of well-formed and approximately cubic crystals. It was found that a very small change in lattice energy (∼0.01%) can be translated into a comparatively much larger change in enthalpy of solution (∼4%) and that the largest changes in properties are expected to occur for particle sizes below ∼100 nm where a steep decrease in lattice energy (spanning a ∼230 kJ·mol-1 range) down to the limit of monomeric NaCl is expected to occur. The experimental findings were corroborated by the results of atom-atom pair potential calculations, which further suggested that the lattice energy within each crystal layer varies from site to site, with the energy differences between adjacent sites decreasing on moving from the periphery to the center of the crystal. The atoms at the outmost surface layer exhibit the lowest lattice energies. Finally the most stable atoms in terms of lattice energy are located in the second layer possibly because repulsive interactions with ions of similar type beyond the crystal surface are absent. © 2015 American Chemical Society.
view abstract doi: 10.1021/jp5124772 2015 • 169 Spheronization of solid lipid extrudates: A novel approach on controlling critical process parameters
Petrovick, G.F. and Pein, M. and Thommes, M. and Breitkreutz, J.
European Journal of Pharmaceutics and Biopharmaceutics 92 15-21 (2015)Solid lipids are non-toxic excipients, which are known to potentially enhance delivery and bioavailability of poorly water-soluble drugs and moreover to mask unpleasant tasting drugs. Multiple unit matrix dosage forms based on solid lipids, such as lipid pellets, can be obtained by solvent-free cold extrusion and spheronization. This method presents advantages in the processing of sensitive substances, such as low process temperatures, the absence of solvents and a drying step. However, the material temperature during the spheronization showed to be critical so far. The process leads to increased material temperatures, causing particle agglomeration and discontinuity of the spheronization. In the present study, extrudates of 0.5 mm in diameter containing metformin hydrochloride, and either semisynthetic hard fat (Witocan® 42/44) or different ternary mixtures based on hard fat, glyceryl trimyristate, and glyceryl distearate, were spheronized. By applying common process parameters, particle agglomeration or material stickiness on equipment walls was observed in preliminary experiments after 2-6 min, depending on the lipid composition. Therefore, an innovative instrumental setup to control the spheronization process was developed utilizing an infrared light source, which was positioned over the particle bed. The new approach enabled a spheronization process that reached the desired spheronization temperature after 2-3 min and neither particle agglomeration nor material adherence occurred even after longer process times. The different formulations, even those based on high amount of solid lipids, were successfully spheronized over 15 min, resulting in small diameter lipid pellets with smooth surface and aspect ratios below 1.3. © 2015 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.ejpb.2015.02.004 2015 • 168 Temporal and spatial variation of the metal-related oxidative potential of PM2.5 and its relation to PM2.5 mass and elemental composition
Yang, A. and Hellack, B. and Leseman, D. and Brunekreef, B. and Kuhlbusch, T.A.J. and Cassee, F.R. and Hoek, G. and Janssen, N.A.H.
Atmospheric Environment 102 62-69 (2015)Oxidative potential (OP) of particulate matter (PM) has been proposed as a more health relevant metric than PM mass. However, little is known about the temporal and spatial variation of OP, which is crucial if OP were to be used as an exposure metric in epidemiological studies. We studied OP on routinely collected PM2.5 samples (every 6th day) from three regional, five urban background, and three street sites over a one-year period across the Netherlands. OP was measured as the ability to generate hydroxyl radicals in the presence of hydrogen peroxide using the electron spin resonance (OPESR).OPESR correlated poorly with PM2.5 mass both spatially (Spearman's rs = 0.29) and temporally (median rs = 0.34). The temporal correlations across sites for OPESR were moderate (median rs = 0.50) compared to PM2.5 (median rs = 0.87), suggesting that exposure misclassification is higher when using OPESR as an exposure metric in time series studies. Street/urban background and street/regional background ratios for OPESR were 1.4 and 2.4 respectively; higher than for PM2.5 (ratio of 1.1 for both street/urban background and street/regional background).This large scale, nationwide study found that PM2.5 correlated poorly with OPESR in space and time. Spatial contrasts were much larger for OPESR than for PM2.5, which offers the possibility to use OPESR to assess long-term exposure health effects. © 2014.
view abstract doi: 10.1016/j.atmosenv.2014.11.053 2015 • 167 The role of calcitonin receptor signalling in polyethylene particle-induced osteolysis
Neuerburg, C. and Wedemeyer, C. and Goedel, J. and Schlepper, R. and Hilken, G. and Schwindenhammer, B. and Schilling, A.F. and Jäger, M. and Kauther, M.D.
Acta Biomaterialia 14 125-132 (2015)The detection of peptides from the calcitonin (CT) family in the periarticular tissue of loosened implants has raised hopes of opening new regenerative therapies in the process of aseptic loosening, which remains the major cause of early implant failure in endoprosthetic surgery. We have previously shown the roles of α-calcitonin gene-related peptide (α-CGRP) and the CALCA gene which encodes α-CGRP/CT in this process. To uncover the role of direct calcitonin receptor (CTR) mediated signalling, we studied particle-induced osteolysis (PIO) in a murine calvaria model with a global deletion of the CTR (CTR-KO) using μCT analysis and histomorphometry. As expected, CTR-KO mice revealed reduced bone volume compared to wild-type (WT) controls (p < 0.05). In CTR-KO mice we found significantly higher RANKL (receptor activator of NF-κB ligand) expression in the particle group than in the control group. The increase in osteoclast numbers by the particles was twice as high as the increase of osteoclasts in the WT mice (400 vs. 200%). Changes in the eroded surface and actual osteolysis due to ultrahigh-molecular-weight polyethylene particles were similar in WTs and CTR-KOs. Taken together, our findings strengthen the relevance of the OPG/RANK/RANKL system in the PIO process. CTR seems to have an effect on osteoclast differentiation in this context. As there were no obvious changes of the amount of PIO in CTR deficiency, regenerative strategies in aseptic loosening of endoprosthetic implants based on peptides arising from the CT family should rather focus on the impact of α-CGRP. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
view abstract doi: 10.1016/j.actbio.2014.11.051 2014 • 166 A study on the influence of particle shape and shape approximation on particle mechanics in a rotating drum using the discrete element method
Höhner, D. and Wirtz, S. and Scherer, V.
Powder Technology 253 256-265 (2014)In this study experimental and numerical investigations with the discrete element method (DEM) on the mechanical interactions of spheres and polyhedral dices in a rotating drum are conducted. In DEM the dices are approximated by polyhedra and smoothed polyhedra respectively and hence allow examining the influence of sharply-edged and smooth particle geometries on the mechanical behavior. Simulation results are in good general agreement with the experiments and hence demonstrate the adequacy of DEM as well as polyhedral and smoothed polyhedral approximation schemes to simulate non-spherical particle geometries. It was observed that an increase of particle angularity leads to an increase of the dynamic angle of repose. On the other hand, while spheres mix faster than the polyhedral dices, no significant difference in the mixing behaviors of the dices can be observed. © 2013 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2013.11.023 2014 • 165 Activation of oxygen evolving perovskites for oxygen reduction by functionalization with Fe-Nx/C groups
Rincón, R.A. and Masa, J. and Mehrpour, S. and Tietz, F. and Schuhmann, W.
Chemical Communications 50 14760-14762 (2014)The incorporation of Fe-Nx/C moieties into perovskites remarkably activates them for the oxygen reduction reaction (ORR) and also leads to notable improvement of their activity towards the oxygen evolution reaction (OER) thus presenting a new route for realizing high performance, low cost bifunctional catalysts for reversible oxygen electrodes. This journal is © the Partner Organisations 2014.
view abstract doi: 10.1039/c4cc06446a 2014 • 164 Aluminum-doped ZnO nanoparticles: Gas-phase synthesis and dopant location
Schilling, C. and Zähres, M. and Mayer, C. and Winterer, M.
Journal of Nanoparticle Research 16 (2014)Aluminum-doped ZnO (AZO) nanoparticles are studied widely as transparent conducting alternatives for indium tin oxide. However, the properties of AZO vary in different investigations not only with the amount of dopant and the particle size, but also with other parameters such as synthesis method and conditions. Hence, AZO nanoparticles, synthesized in the gas phase, were investigated to study the influence of the synthesis parameters dopant level, reactor temperature and residence time in the reaction zone on the particle characteristics. The local structure of the dopant in semiconductors determines whether the doping is functional, i.e., whether mobile charge carriers are generated. Therefore, information obtained from 27Al solid-state NMR spectroscopy, X-ray diffraction, photoluminescence and UV-Vis spectroscopy was used to understand how the local structure influences particles characteristics and how the local structure itself can be influenced by the synthesis parameters. In addition to AZO particles of different Al content, pure ZnO, Al2O3, ZnAl2O4 and core-shell particles of ZnO and Al2O3 were synthesized for comparison and aid to a deeper understanding of the formation of AZO nanoparticles in the gas phase. © 2014 Springer Science+Business Media.
view abstract doi: 10.1007/s11051-014-2506-z 2014 • 163 Apoptotic, inflammatory, and fibrogenic effects of two different types of multi-walled carbon nanotubes in mouse lung
Van Berlo, D. and Wilhelmi, V. and Boots, A.W. and Hullmann, M. and Kuhlbusch, T.A.J. and Bast, A. and Schins, R.P.F. and Albrecht, C.
Archives of Toxicology 88 1725-1737 (2014)There is increasing concern about the toxicity of inhaled multi-walled carbon nanotubes (MWCNTs). Pulmonary macrophages represent the primary cell type involved in the clearance of inhaled particulate materials, and induction of apoptosis in these cells has been considered to contribute to the development of lung fibrosis. We have investigated the apoptotic, inflammogenic, and fibrogenic potential of two types of MWCNTs, characterised by a contrasting average tube length and entanglement/agglomeration. Both nanotube types triggered H2O2 formation by RAW 264.7 macrophages, but in vitro toxicity was exclusively seen with the longer MWCNT. Both types of nanotubes caused granuloma in the mouse lungs. However, the long MWCNT induced a more pronounced pro-fibrotic (mRNA expression of matrix metalloproteinase-8 and tissue inhibitor of metalloproteinase-1) and inflammatory (serum level of monocyte chemotactic protein-1) response. Masson trichrome staining also revealed epithelial cell hyperplasia for this type of MWCNT. Enhanced apoptosis was detected by cleaved caspase 3 immunohistochemistry in lungs of mice treated with the long and rigid MWCNT and, to a lesser extent, with the shorter, highly agglomerated MWCNT. However, staining was merely localised to granulomatous foci, and neither of the MWCNTs induced apoptosis in vitro, evaluated by caspase 3/7 activity in RAW 264.7 cells. In addition, our study reveals that the inflammatory and pro-fibrotic effects of MWCNTs in the mouse lung can vary considerably depending on their composition. The in vitro analysis of macrophage apoptosis appears to be a poor predictor of their pulmonary hazard. © 2014 Springer-Verlag.
view abstract doi: 10.1007/s00204-014-1220-z 2014 • 162 Artificial oxygen carriers based on perfluorodecalin-filled poly(n-butyl-cyanoacrylate) nanocapsules
Stephan, C. and Schlawne, C. and Grass, S. and Waack, I.N. and Ferenz, K.B. and Bachmann, M. and Barnert, S. and Schubert, R. and Bastmeyer, M. and De Groot, H. and Mayer, C.
Journal of Microencapsulation 31 284-292 (2014)Poly(n-butyl-cyanoacrylate)-nanocapsules filled by perfluorodecalin (PFD) are proposed as potential oxygen carriers for blood substitute. The capsule dispersion is prepared via interfacial polymerisation from a PFD emulsion in water which in turn is generated by spontaneous phase separation. The resulting dispersion is capable of carrying approximately 10% of its own volume of gaseous oxygen, which is approximately half of the capacity of human blood. The volumes of the organic solvents and water are varied within a wide range, connected to a change of the capsule radius between 200 and 400-nm. The principal suitability of the capsule dispersion for intravenous application is proven in first physiological experiments. A total amount of 10-ml/kg body weight has been infused into rats, with the dispersion supernatant and a normal saline solution as controls. After the infusion of nanocapsules, the blood pressure as well as the heart rate remains constant on a normal level. © 2014 Informa UK Ltd. All rights reserved: reproduction in whole or part not permitted.
view abstract doi: 10.3109/02652048.2013.843600 2014 • 161 Assessment of a cylindrical and a rectangular plate differential mobility analyzer for size fractionation of nanoparticles at high-aerosol flow rates
Hontañón, E. and Rouenhoff, M. and Azabal, A. and Ramiro, E. and Kruis, F.E.
Aerosol Science and Technology 48 333-339 (2014)An existing differential mobility analyzer (DMA) of cylindrical electrodes and a novel DMA of rectangular plate electrodes are demonstrated for size fractionation of nanoparticles at high-aerosol flow rates in this work. The two DMAs are capable of delivering monodisperse size selected nanoparticles (SMPS σg < 1.1) at gas flow rates ranging from 200 slm to 500 slm. At an aerosol flow rate of 200 slm, the maximum attainable particle mean size is of about 20 nm for the cylindrical DMA and of nearly 50 nm for the rectangular plate DMA. The number concentration of the monodisperse nanoparticles delivered by the high-flow DMAs spans from 104 cm-3 to 10 6 cm-3 depending upon the particle mean size and particle size dispersion. Copyright © 2014 American Association for Aerosol Research.
view abstract doi: 10.1080/02786826.2013.875116 2014 • 160 Behavior of nanoscale titanium dioxide in laboratory wastewater treatment plants according to OECD 303 A
Gartiser, S. and Flach, F. and Nickel, C. and Stintz, M. and Damme, S. and Schaeffer, A. and Erdinger, L. and Kuhlbusch, T.A.J.
Chemosphere 104 197-204 (2014)The fate assessment of nanomaterials in municipal sewage treatment plants (STP) is a crucial step for their environmental risk assessment and may be assessed by monitoring full scale STP, dosage to medium scale pilot STP or by laboratory testing. For regulatory purposes preferably standardised test protocols such as the OECD guidelines for testing of chemicals should be used. However, these test protocols have not yet been specifically designed for nanoparticles. Therefore, the fate and behavior of a TiO2 nanomaterial (P25, average hydrodynamic diameter < 250nm) was investigated in laboratory sewage treatment plants according to the OECD Guideline for the Testing of Chemicals 303 A. It is concluded that this guideline is applicable for the testing of nanomaterials if modifications regarding the dosage, nitrifying conditions, and a characterisation of the nanoparticles in the effluent are applied. A compilation of the cumulative mass balance by comparison of the total dosage added with the amount in the outflow and in the activated sludge is recommended. In this study, the majority of the TiO2 nanomaterial (>95%) was retained in the sewage sludge and only 3-4% was found in the effluent. No effect of the TiO2 nanomaterials on the biodegradation or nitrification was observed. © 2013 Elsevier Ltd.
view abstract doi: 10.1016/j.chemosphere.2013.11.015 2014 • 159 Carbon monoxide-assisted size confinement of bimetallic alloy nanoparticles
Cui, C. and Gan, L. and Neumann, M. and Heggen, M. and Roldan Cuenya, B. and Strasser, P.
Journal of the American Chemical Society 136 4813-4816 (2014)Colloid-based chemical synthesis methods of bimetallic alloy nanoparticles (NPs) provide good monodispersity, yet generally show a strong variation of the resulting mean particle size with alloy composition. This severely compromises accurate correlation between composition of alloy particles and their size-dependent properties. To address this issue, a general CO adsorption-assisted capping ligand-free solvothermal synthesis method is reported which provides homogeneous bimetallic NPs with almost perfectly constant particle size over an unusually wide compositional range. Using Pt-Ni alloy NPs as an example, we show that variation of the reaction temperature between 160 and 240 °C allows for precise control of the resulting alloy particle bulk composition between 15 and 70 atomic % Ni, coupled with a constant mean particle size of ∼4 nm. The size-confining and Ni content-controlling role of CO during the nucleation and growth processes are investigated and discussed. Data suggest that size-dependent CO surface chemisorption and reversible Ni-carbonyl formation are key factors for the achievement of a constant particle size and temperature-controlled Ni content. To demonstrate the usefulness of the independent control of size and composition, size-deconvoluted relations between composition and electrocatalytic properties are established. Refining earlier reports, we uncover intrinsic monotonic relations between catalytic activity and initial Ni content, as expected from theoretical considerations. © 2014 American Chemical Society.
view abstract doi: 10.1021/ja4124658 2014 • 158 Comparison of different characterization methods for nanoparticle dispersions before and after aerosolization
Fissan, H. and Ristig, S. and Kaminski, H. and Asbach, C. and Epple, M.
Analytical Methods 6 7324-7334 (2014)A well-known and accepted aerosol measurement technique, the scanning mobility particle sizer (SMPS), is applied to characterize colloidally dispersed nanoparticles. To achieve a transfer from dispersed particles to aerosolized particles, a newly developed nebulizer (N) is used that, unlike commonly used atomizers, produces significantly smaller droplets and therefore reduces the problem of the formation of residual particles. The capabilities of this new instrument combination (N + SMPS) for the analysis of dispersions were investigated, using three different dispersions, i.e. gold-PVP nanoparticles (∼20 nm), silver-PVP nanoparticles (∼70 nm) and their 1:1 (m:m) mixture. The results are compared to scanning electron microscopy (SEM) measurements and two frequently applied techniques for characterizing colloidal systems: Dynamic light scattering (DLS) and analytical disc centrifugation (ADC). The differences, advantages and disadvantages of each method are discussed, especially with respect to the size resolution of the techniques and their ability to distinguish the particle sizes of the mixed dispersion. While DLS is, as expected, unable to resolve the binary dispersion, SEM, ADC and SMPS are able to give quantitative information on the two particle sizes. However, while the high-resolving ADC is limited due to the dependency on a predefined density of the investigated system, the transfer of dispersed particles into an aerosol and subsequent analysis with SMPS are an adequate way to characterize binary systems, independent of the density of concerned particles, but matching the high resolution of the ADC. We show that it is possible to use the well-established aerosol measurement technique (N + SMPS) in colloid science with all its advantages concerning size resolution and accuracy. © the Partner Organisations 2014.
view abstract doi: 10.1039/c4ay01203h 2014 • 157 Comparison of instruments for particle number size distribution measurements in air quality monitoring
Price, H.D. and Stahlmecke, B. and Arthur, R. and Kaminski, H. and Lindermann, J. and Däuber, E. and Asbach, C. and Kuhlbusch, T.A.J. and BéruBé, K.A. and Jones, T.P.
Journal of Aerosol Science 76 48-55 (2014)Number size distributions of airborne particles are relevant to fields including ambient monitoring, pharmaceutical and automotive measurements. A number of commercially available instruments can be used to determine particle number size distributions including the Electrical Low Pressure Impactor (ELPI), Scanning Mobility Particle Sizer (SMPS), Fast Mobility Particle Sizer (FMPS) and the Aerodynamic Particle Sizer (APS). The comparability of the data provided by these instruments has not been fully tested for different kinds of aerosols. This study compared number size distributions of laboratory generated aerosols (TiO2, NaCl, fumed silica and soot) in a wind tunnel. Reasonable agreement was noted between the different instruments, though there were divergences. For example the ELPI was inconsistent at the upper and lower limits of its working size (at low concentrations). Instruments responded variably to different particle types, which has important implications for sampling heterogeneous particle mixtures such as those found in urban air. This study highlights the need for caution when comparing data obtained from different particle instruments, and demonstrates the requirement for further comparison studies in controlled settings using an assortment of particle types with the aim to standardise and harmonise particle sampling protocols. © 2014 Elsevier Ltd.
view abstract doi: 10.1016/j.jaerosci.2014.05.001 2014 • 156 Comparison of silver nanoparticles stored under air or argon with respect to the induction of intracellular free radicals and toxic effects toward keratinocytes
Ahlberg, S. and Meinke, M.C. and Werner, L. and Epple, M. and Diendorf, J. and Blume-Peytavi, U. and Lademann, J. and Vogt, A. and Rancan, F.
European Journal of Pharmaceutics and Biopharmaceutics 88 651-657 (2014)Bacterial infections decreased considerably after the discovery of antibiotics. Nevertheless, because of the rising rate of infections caused by antibiotic-resistant bacteria strains, the search for new bactericidal agents has again become a crucial topic in clinical medicine. Silver nanoparticles (AgNP) have a huge potential in dermatology and wound care management because of their ability to release silver ions (Ag+ ions) in a prolonged and sustained way. However, negative effects of silver on the patient's cells should not be underestimated. Furthermore, it has been controversially discussed whether AgNP are responsible for nanoparticle-specific outcomes or not. In this study, we investigated the effects of AgNP on human skin keratinocytes (HaCaT) in order to better understand the mechanisms of cytotoxicity and to improve the use of this highly reactive biocide in wound healing. We found that most of the cells with internalized AgNP displayed the typical morphological signs of apoptosis. The cell viability assay (XTT) showed concentration-dependent toxic effects of the AgNP toward HaCaT cells. The generation of reactive oxygen species (ROS) induced by AgNP was investigated in cell suspensions by means of electron paramagnetic resonance (EPR) spectroscopy. In order to distinguish between the effects of Ag+ ions released during AgNP storage and those of Ag+ ions released after nanoparticle application, we compared AgNP stored under air (O2) with AgNP stored under argon (Ar). Dispersions of AgNP stored under Ar have a low content of Ag+ ions because of the absence of oxygen which is needed for oxidative dissolution. The results show that Ag+ ions released during particle storage are responsible for most of the ROS produced during 1 h incubation with the cells. AgNP (Ar) also induced intracellular ROS but to a much smaller extent compared to AgNP (O2). These findings highlight the complexity of experiments to assess the toxicity of AgNP and suggest the possibility of reducing AgNP toxic effects by storing AgNP formulations and even silver-containing wound dressing under an inert gas atmosphere. © 2014 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.ejpb.2014.07.012 2014 • 155 Determination of the relevant charging parameters for the modeling of unipolar chargers
Domat, M. and Kruis, F.E. and Fernandez-Diaz, J.M.
Journal of Aerosol Science 71 16-28 (2014)A model for unipolar charging of nanoparticles based on the Fuchs birth-and-death theory is developed. It includes both diffusional and electrical losses for particles and ions. Electrical losses are modeled by inclusion of a radial electric field which is caused by space charge. The model can be used to obtain the initial ion concentration and mean radial electric field from data of charge distribution fractions, without additional measurements. It was successfully applied to results from three different unipolar chargers. In all cases, good agreement between experimental and modeling results has been obtained. The model can be used to assist the operation of unipolar chargers, e.g. by predicting charging efficiencies for particle sizes which are not experimentally accessible. © 2014 Elsevier Ltd.
view abstract doi: 10.1016/j.jaerosci.2014.01.005 2014 • 154 Effects of laser sintering processing time and temperature on changes in polyamide 12 powder particle size, shape and distribution
Mielicki, C. and Gronhoff, B. and Wortberg, J.
AIP Conference Proceedings 1593 728-731 (2014)In laser sintering (LS) un-molten Polyamide 12 (PA12) powder is usually re-used (recycled) in further processes. However, LS processing time at powder bed temperature leads to material property changes. As a consequence, un-molten PA12 powder that is re-used or recycled in further processes leads to process and part properties deviations. In this context, powder particle size, shape and distribution is assumed to affect surface roughness and porosity of LS parts. In order to investigate this process effect on changes in powder size, shape and distribution, PA12 powder was systematically aged in a vacuum oven at conditions close to the LS process. According to this procedure, polymeric powder was obtained with aging times up to 120 hours and analyzed by dynamic image analysis. At first, fresh powder was investigated as a reference. The effect of LS processing time and temperature, i.e. powder bed temperature of approx. 174°C was measured with respect to changes in size distribution and shape whereas particles were considered of size up to 500μm. The influence of LS processing time at powder bed temperature was found to be neither significant on changes in particle size nor distribution. With respect to particle shape, a higher deviation to the reference was observed for particle size bigger than 100 μm and longer aging times. Consequently, influences on particle shape changes on surface roughness are assumed to be more likely than influences on part porosity due to LS processing conditions. © 2014 American Institute of Physics.
view abstract doi: 10.1063/1.4873880 2014 • 153 Effects of silver nitrate and silver nanoparticles on a planktonic community: General trends after short-term exposure
Boenigk, J. and Beisser, D. and Zimmermann, S. and Bock, C. and Jakobi, J. and Grabner, D. and Großmann, L. and Rahmann, S. and Barcikowski, S. and Sures, B.
PLoS ONE 9 (2014)Among metal pollutants silver ions are one of the most toxic forms, and have thus been assigned to the highest toxicity class. Its toxicity to a wide range of microorganisms combined with its low toxicity to humans lead to the development of a wealth of silver-based products in many bactericidal applications accounting to more than 1000 nano-technology-based consumer products. Accordingly, silver is a widely distributed metal in the environment originating from its different forms of application as metal, salt and nanoparticle. A realistic assessment of silver nanoparticle toxicity in natural waters is, however, problematic and needs to be linked to experimental approaches. Here we apply metatranscriptome sequencing allowing for elucidating reactions of whole communities present in a water sample to stressors. We compared the toxicity of ionic silver and ligand-free silver nanoparticles by short term exposure on a natural community of aquatic microorganisms. We analyzed the effects of the treatments on metabolic pathways and species composition on the eukaryote metatranscriptome level in order to describe immediate molecular responses of organisms using a community approach. We found significant differences between the samples treated with 5 μg/L AgNO 3 compared to the controls, but no significant differences in the samples treated with AgNP compared to the control samples. Statistical analysis yielded 126 genes (KO-IDs) with significant differential expression with a false discovery rate (FDR) < 0.05 between the control (KO) and AgNO3 (NO3) groups. A KEGG pathway enrichment analysis showed significant results with a FDR below 0.05 for pathways related to photosynthesis. Our study therefore supports the view that ionic silver rather than silver nanoparticles are responsible for silver toxicity. Nevertheless, our results highlight the strength of metatranscriptome approaches for assessing metal toxicity on aquatic communities. © 2014 Boenigk et al.
view abstract doi: 10.1371/journal.pone.0095340 2014 • 152 Elemental composition of particulate matter and the association with lung function
Eeftens, M. and Hoek, G. and Gruzieva, O. and Mölter, A. and Agius, R. and Beelen, R. and Brunekreef, B. and Custovic, A. and Cyrys, J. and Fuertes, E. and Heinrich, J. and Hoffmann, B. and De Hoogh, K. and Jedynska, A. and Keuke...
Epidemiology 25 648-657 (2014)BACKGROUND: Negative effects of long-term exposure to particulate matter (PM) on lung function have been shown repeatedly. Spatial differences in the composition and toxicity of PM may explain differences in observed effect sizes between studies. METHODS: We conducted a multicenter study in 5 European birth cohorts - BAMSE (Sweden), GINIplus and LISAplus (Germany), MAAS (United Kingdom), and PIAMA (The Netherlands) - for which lung function measurements were available for study subjects at the age of 6 or 8 years. Individual annual average residential exposure to copper, iron, potassium, nickel, sulfur, silicon, vanadium, and zinc within PM smaller than 2.5 μm (PM2.5) and smaller than 10 μm (PM10) was estimated using land-use regression models. Associations between air pollution and lung function were analyzed by linear regression within cohorts, adjusting for potential confounders, and then combined by random effects meta-analysis. RESULTS: We observed small reductions in forced expiratory volume in the first second, forced vital capacity, and peak expiratory flow related to exposure to most elemental pollutants, with the most substantial negative associations found for nickel and sulfur. PM10 nickel and PM10 sulfur were associated with decreases in forced expiratory volume in the first second of 1.6% (95% confidence interval = 0.4% to 2.7%) and 2.3% (-0.1% to 4.6%) per increase in exposure of 2 and 200 ng/m, respectively. Associations remained after adjusting for PM mass. However, associations with these elements were not evident in all cohorts, and heterogeneity of associations with exposure to various components was larger than for exposure to PM mass. CONCLUSIONS: Although we detected small adverse effects on lung function associated with annual average levels of some of the evaluated elements (particularly nickel and sulfur), lower lung function was more consistently associated with increased PM mass. Copyright © 2014 by Lippincott Williams & Wilkins.
view abstract doi: 10.1097/EDE.0000000000000136 2014 • 151 Enhancing solar cell efficiency by lenses on the nano- And microscale
Schmid, M. and Manley, P.
Proceedings of SPIE - The International Society for Optical Engineering 9178 (2014)Metallic nanoparticles exhibiting plasmonic effects as well as dielectric nanoparticles coupling the light into resonant modes have both shown successful application to photovoltaics. On the larger scale, microconcentrator optics promise to enhance solar cell efficiency and reduce material consumption. Here we want to make the link between concentrators on the nano- And on the microscale. From metallic nanospheres we turn to dielectric ones and then look at increasing radii to approach concentrator optics on the mircoscale. The nano- And microlenses are investigated with respect to their interaction with light using 3D simulations with the finite element method. Resulting maps of local electric field distributions reveal the focusing behavior of the dielectric spheres. For larger lens sizes, ray tracing calculations can be applied which give ray distributions in agreement with areas of high electric field intensities. Calculations of back focal lengths using ray tracing coincide with results from geometrical optics simulations. They give us insight into how the focal length can be tuned as a function of particle size, but also depending on the substrate refractive index and the shape of the microlens. Turning from spherical to segment-shaped lenses allows us to approach the realistic case of microconcentrator optics and to draw conclusions about focus tuning and system design. Despite the similarities of focusing behavior we find for the nano- And the microlenses, the integration into solar cells needs to be carefully adjusted, depending on the ambition of material saving, concentration level, focal distance and lens size, all being closely related. © 2014 SPIE.
view abstract doi: 10.1117/12.2061132 2014 • 150 Exceptional size-dependent activity enhancement in the electroreduction of CO2 over Au nanoparticles
Mistry, H. and Reske, R. and Zeng, Z. and Zhao, Z.-J. and Greeley, J. and Strasser, P. and Cuenya, B.R.
Journal of the American Chemical Society 136 16473-16476 (2014)The electrocatalytic reduction of CO2 to industrial chemicals and fuels is a promising pathway to sustainable electrical energy storage and to an artificial carbon cycle, but it is currently hindered by the low energy efficiency and low activity displayed by traditional electrode materials. We report here the size-dependent catalytic activity of micelle-synthesized Au nanoparticles (NPs) in the size range of ∼1-8 nm for the electroreduction of CO2 to CO in 0.1 M KHCO3. A drastic increase in current density was observed with decreasing NP size, along with a decrease in Faradaic selectivity toward CO. Density functional theory calculations showed that these trends are related to the increase in the number of low-coordinated sites on small NPs, which favor the evolution of H2 over CO2 reduction to CO. We show here that the H2/CO product ratio can be specifically tailored for different industrial processes by tuning the size of the catalyst particles. © 2014 American Chemical Society.
view abstract doi: 10.1021/ja508879j 2014 • 149 Gold and silver nanoparticle monomers are non-SERS-active: A negative experimental study with silica-encapsulated Raman-reporter-coated metal colloids
Zhang, Y. and Walkenfort, B. and Yoon, J.H. and Schlücker, S. and Xie, W.
Physical Chemistry Chemical Physics 17 21120-21126 (2014)Noble metal nanoparticles (NPs) are the most commonly employed plasmonic substrates in surface-enhanced Raman scattering (SERS) experiments. Computer simulations show that monomers of Ag and Au nanocrystals ("spherical" NPs) do not exhibit a notable plasmonic enhancement, i.e., they are essentially non-SERS-active. However, in experiments, SERS enhanced by spherical NP colloids has been frequently reported. This implies that the monomers do not have strong SERS activity, but detectable enhancement should more or less be there. Because of the gap between theory and practice, it is important to demonstrate experimentally how SERS-active the metal colloid actually is and, in case a SERS signal is observed, where it originates from. In particular the aggregation of the colloid, induced by high centrifugal forces in washing steps or due to a harsh ionic environment of the suspension medium, should be controlled since it is the very high SERS activity of NP clusters which dominates the overall SERS signal of the colloid. We report here the experimental evaluation of the SERS activity of 80 nm Au and Ag NP monomers. Instead of showing fancy nanostructures and super SERS enhancement, we present the method on how to obtain negative experimental data. In this approach, no SERS signal was obtained from the colloid with a Raman reporter on the metal surface when the NPs were encapsulated carefully within a thick silica shell. Without silica encapsulation, if a very low centrifugation speed is used for the washing steps, only a negligible SERS signal can be detected even at very high NP concentrations. In contrast, strong SERS signals can be detected when the NPs are suspended in acidic solutions. These results indicate that Au and Ag NP monomers essentially exhibit no SERS activity of practical relevance. © the Owner Societies 2015.
view abstract doi: 10.1039/c4cp05073h 2014 • 148 Gold nanoparticles interfere with sperm functionality by membrane adsorption without penetration
Taylor, U. and Barchanski, A. and Petersen, S. and Kues, W.A. and Baulain, U. and Gamrad, L. and Sajti, L. and Barcikowski, S. and Rath, D.
Nanotoxicology 8 118-127 (2014)To examine gold nanoparticle reprotoxicity, bovine spermatozoa were challenged with ligand-free or oligonucleotide-conjugated gold nanoparticles synthesized purely without any surfactants by laser ablation. Sperm motility declined at nanoparticle mass dose of 10 μg/ml (corresponding to ∼14 000 nanoparticles per sperm cell) regardless of surface modification. Sperm morphology and viability remained unimpaired at all concentrations. Transmission electron microscopy showed an modification dependant attachment of nanoparticles to the cell membrane of spermatozoa, but provided no evidence for nanoparticle entrance into sperm cells. A molecular examination revealed a reduction of free thiol residues on the cell membrane after nanoparticle exposure, which could explain the decrease in sperm motility. Sperm fertilising ability decreased after exposure to 10 μg/ml of ligand-free nanoparticles indicating that agglomerated ligand-free nanoparticles interfere with membrane properties necessary for fertilisation. In conclusion, nanoparticles may impair key sperm functions solely by interacting with the sperm surface membrane. © 2014 Informa UK Ltd. All rights reserved.
view abstract doi: 10.3109/17435390.2013.859321 2014 • 147 Impact of the specific surface area on the memory effect in Li-ion batteries: The case of anatase TiO2
Madej, E. and Mantia, F.L. and Schuhmann, W. and Ventosa, E.
Advanced Energy Materials 4 (2014)Until recently, the memory effect was believed to be absent in Li-ion battery materials. Here, the memory effect is clearly observed in anatase TiO2 nanoparticles when they are used as the negative electrode material in Li-ion batteries. Additionally, the memory effect strongly decreases with increasing specific surface area of the TiO2 sample. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA.
view abstract doi: 10.1002/aenm.201400829 2014 • 146 Influence of molecular hydrogen on acetylene pyrolysis: Experiment and modeling
Aghsaee, M. and Dürrstein, S.H. and Herzler, J. and Böhm, H. and Fikri, M. and Schulz, C.
Combustion and Flame 161 2263-2269 (2014)The effect of molecular hydrogen on the formation of molecular carbonaceous species important for soot formation is studied through a combination of shock-tube experiments with high-repetition-rate time-of-flight mass spectrometry and detailed chemistry modeling. The experiment allows to simultaneously measure the concentration-time profiles for various species with a time resolution of 10μs. Concentration histories of reactants and polyacetylene intermediates (C2xH2, x=1-4) are measured during the pyrolysis of acetylene with and without H2 added to the gas mixture for a wide range of conditions. In the 1760-2565K temperature range, reasonable agreement between the experiment and the model predictions for C2H2, C4H2, C6H2, and C8H2 is achieved. H2 addition leads to the depletion of important building blocks for particle formation, namely of polyacetylenes due to an enhanced consumption of important radicals by H2, which are required for the fast build-up of carbonaceous material. © 2014 The Combustion Institute.
view abstract doi: 10.1016/j.combustflame.2014.03.012 2014 • 145 Investigation into mixing capability and solid dispersion preparation using the DSM Xplore Pharma Micro Extruder
Sakai, T. and Thommes, M.
Journal of Pharmacy and Pharmacology 66 218-231 (2014)Objectives The goal of this investigation was to qualify the DSM Xplore Pharma Micro Extruder as a formulation screening tool for early-stage hot-melt extrusion. Methods Dispersive and distributive mixing was investigated using soluplus, copovidone or basic butylated methacrylate copolymer with sodium chloride (NaCl) in a batch size of 5 g. Eleven types of solid dispersions were prepared using various drugs and carriers in batches of 5 g in accordance with the literature. Key findings The dispersive mixing was a function of screw speed and recirculation time and the particle size was remarkably reduced after 1 min of processing, regardless of the polymers. An inverse relationship between the particle size and specific mechanical energy (SME) was also found. The SME values were higher than those in large-scale extruders. After 1 min recirculation at 200 rpm, the uniformity of NaCl content met the criteria of the European Pharmacopoeia, indicating that distributive mixing was achieved in this time. For the solid dispersions preparations, the results from different scanning calorimetry, powder X-ray diffractometry and in-vitro dissolution tests confirmed that all solid-dispersion systems were successfully prepared. Conclusions These findings demonstrated that the extruder is a useful tool to screen solid-dispersion formulations and their material properties on a small scale. © 2013 Royal Pharmaceutical Society.
view abstract doi: 10.1111/jphp.12085 2014 • 144 Investigations of the effect of electrode gap on the performance of a corona charger having separated corona and charging zones
Domat, M. and Kruis, F.E. and Fernandez-Diaz, J.M.
Journal of Aerosol Science 68 1-13 (2014)An efficient and a versatile unipolar corona charger was developed. It has indirect charging characteristics, with corona and charging regions separated. Ions were generated by a needle electrode and then driven to the charging region by a sheath flow in order to reduce the electrostatic loss of nanoparticles. The distance of the electrode to the walls can be adjusted by a micrometer, modifying the onset voltage and N it-product, and therefore the intrinsic and extrinsic charging efficiencies and loss of charged particles. Experimental results indicate that the generated ion current is practically the same independent of the variation in the applied voltage or corona current, but varying the electrode gap distance seems to be a much more efficient way to regulate the N it-product. The charging efficiency can vary from high values, comparable to the higher efficiency chargers presented in the literature, to lower levels such as reached with bipolar chargers. © 2013 Elsevier Ltd.
view abstract doi: 10.1016/j.jaerosci.2013.08.017 2014 • 143 Mössbauer study of temperature-dependent cycloidal ordering in BiFeO3 nanoparticles
Landers, J. and Salamon, S. and Escobar Castillo, M. and Lupascu, D.C. and Wende, H.
Nano Letters 14 6061-6065 (2014)To study the effects of different temperatures and particle sizes on the anharmonic cycloidal spin structure in BiFeO3 nanoparticles, Mössbauer spectroscopy was applied to three sets of particles with different mean diameters in the range of 54 nm to 1.6 μm at temperatures between 4.2 and 800 K. The paramagnetic transition showed a distinct broadening upon decreasing particle size with Néel temperatures decreasing from 652 to 631 K. The anharmonicity of the long-range cycloidal structure, calculated from experimental Mössbauer spectra, is revealed to decrease upon rising temperature, starting at 150-200 K and reaching the harmonic state at about 400 K. © 2014 American Chemical Society.
view abstract doi: 10.1021/nl5031375 2014 • 142 MSC-derived exosomes: A novel tool to treat therapy-refractory graft-versus-host disease
Kordelas, L. and Rebmann, V. and Ludwig, A.-K. and Radtke, S. and Ruesing, J. and Doeppner, T.R. and Epple, M. and Horn, P.A. and Beelen, D.W. and Giebel, B.
Leukemia 28 970-973 (2014)
doi: 10.1038/leu.2014.41 2014 • 141 Multiple reentrant glass transitions in confined hard-sphere glasses
Mandal, S. and Lang, S. and Gross, M. and Oettel, M. and Raabe, D. and Franosch, T. and Varnik, F.
Nature Communications 5 (2014)Glass-forming liquids exhibit a rich phenomenology upon confinement. This is often related to the effects arising from wall-fluid interactions. Here we focus on the interesting limit where the separation of the confining walls becomes of the order of a few particle diameters. For a moderately polydisperse, densely packed hard-sphere fluid confined between two smooth hard walls, we show via event-driven molecular dynamics simulations the emergence of a multiple reentrant glass transition scenario upon a variation of the wall separation. Using thermodynamic relations, this reentrant phenomenon is shown to persist also under constant chemical potential. This allows straightforward experimental investigation and opens the way to a variety of applications in micro-and nanotechnology, where channel dimensions are comparable to the size of the contained particles. The results are in line with theoretical predictions obtained by a combination of density functional theory and the mode-coupling theory of the glass transition. © 2014 Macmillan Publishers Limited.
view abstract doi: 10.1038/ncomms5435 2014 • 140 Nanoparticle impacts reveal magnetic field induced agglomeration and reduced dissolution rates
Tschulik, K. and Compton, R.G.
Physical Chemistry Chemical Physics 16 13909-13913 (2014)Superparamagnetic nanoparticles (NPs) are used in a variety of magnetic field-assisted chemical and medical applications, yet little of their fate during magnetic field interrogation is known. Here, fundamental and new insights in this are gained by cathodic particle coulometry. This methodology is used to study individual Fe3O4 NPs in the presence and absence of a magnetic field. It is first noticed that no major NP agglomeration occurs in the absence of a magnetic field even in a suspension of high ionic strength. In contrast, a significant magnetic field-induced agglomeration of NPs is observed in a magnetic field. A second new finding is that the dissolution of Fe 3O4 NPs is strongly inhibited in a magnetic field. This is explained as a result of the magnetic field gradient force trapping the released Fe2+ ions near the surface of a magnetized Fe 3O4 NP and thus hindering the mass-transport controlled NP dissolution. Consequently, fundamental magnetic field effects are measured and quantified on both the single NP scale and in suspension and two novel effects are discovered. This journal is © the Partner Organisations 2014.
view abstract doi: 10.1039/c4cp01618a 2014 • 139 Nanoparticle release from dental composites
Van Landuyt, K.L. and Hellack, B. and Van Meerbeek, B. and Peumans, M. and Hoet, P. and Wiemann, M. and Kuhlbusch, T.A.J. and Asbach, C.
Acta Biomaterialia 10 365-374 (2014)Dental composites typically contain high amounts (up to 60 vol.%) of nanosized filler particles. There is a current concern that dental personnel (and patients) may inhale nanosized dust particles (< 100 nm) during abrasive procedures to shape, finish or remove restorations but, so far, whether airborne nanoparticles are released has never been investigated. In this study, composite dust was analyzed in real work conditions. Exposure measurements of dust in a dental clinic revealed high peak concentrations of nanoparticles in the breathing zone of both dentist and patient, especially during aesthetic treatments or treatments of worn teeth with composite build-ups. Further laboratory assessment confirmed that all tested composites released very high concentrations of airborne particles in the nanorange (>106 cm-3). The median diameter of airborne composite dust varied between 38 and 70 nm. Electron microscopic and energy dispersive X-ray analysis confirmed that the airborne particles originated from the composite, and revealed that the dust particles consisted of filler particles or resin or both. Though composite dust exhibited no significant oxidative reactivity, more toxicological research is needed. To conclude, on manipulation with the bur, dental composites release high concentrations of nanoparticles that may enter deeply into the lungs. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
view abstract doi: 10.1016/j.actbio.2013.09.044 2014 • 138 Ostwald-Freundlich diffusion-limited dissolution kinetics of nanoparticles
Ely, D.R. and Edwin García, R. and Thommes, M.
Powder Technology 257 120-123 (2014)For many years, nanoparticles have garnered increasing interest in pharmaceutical investigations. It is well known that the solubility of nanoparticles increases with decreasing size due to the Gibbs-Thomson effect. However, there are currently no analytical models to describe the kinetics of nanoparticle dissolution. The purpose of this article is to provide a Thermodynamics-based description of the kinetics of nanoparticle dissolution. In particular, the Ostwald-Freundlich relation is used to correct dissolution times for small particles, which have higher solubilities than larger particles. The developed model is an extension of the Hixson-Crowell cube root law in which the total normalized dissolution time is corrected by a "solubility size factor" that approaches unity for increasing initial particle size. This model enables rapid estimation of the total dissolution time of spherical nanoparticles in a gently agitated, zero solute concentration reservoir. The total dissolution time predicted differs from Hixson-Crowell by nearly 10% for initial particle sizes fifty times larger than the characteristic particle size, and increases to more than a factor of six at the characteristic particle size. This work provides a physics-based description of the nanoparticle dissolution kinetics and details the reaches and limitations of the developed model. The theoretical framework provided herein is valid for a wide range of dissolution processes and size scales affording it a high level of practicality. © 2014 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2014.01.095 2014 • 137 Oxidative potential of particulate matter collected at sites with different source characteristics
Janssen, N.A.H. and Yang, A. and Strak, M. and Steenhof, M. and Hellack, B. and Gerlofs-Nijland, M.E. and Kuhlbusch, T. and Kelly, F. and Harrison, R. and Brunekreef, B. and Hoek, G. and Cassee, F.
Science of the Total Environment 472 572-581 (2014)Background: The oxidative potential (OP) of particulate matter (PM) has been proposed as a more health relevant metric than PM mass. Different assays exist for measuring OP and little is known about how the different assays compare. Aim: To assess the OP of PM collected at different site types and to evaluate differences between locations, size fractions and correlation with PM mass and PM composition for different measurement methods for OP. Methods: PM2.5 and PM10 was sampled at 5 sites: an underground station, a farm, 2 traffic sites and an urban background site. Three a-cellular assays; dithiothreitol (OPDTT), electron spin resonance (OPESR) and ascorbate depletion (OPAA) were used to characterize the OP of PM. Results: The highest OP was observed at the underground, where OP of PM10 was 30 (OPDTT) to >600 (OPESR) times higher compared to the urban background when expressed as OP/m3 and 2-40 times when expressed as OP/μg. For the outdoor sites, samples from the farm showed significantly lower OPESR and OPAA, whereas samples from the continuous traffic site showed the highest OP for all assays. Contrasts in OP between sites were generally larger than for PM mass and were lower for OPDTT compared to OPESR and OPAA. Furthermore, OPDTT/μg was significantly higher in PM2.5 compared to PM10, whereas the reverse was the case for OPESR. OPESR and OPAA were highly correlated with traffic-related PM components (i.e. EC, Fe, Cu, PAHs), whereas OPDTT showed the highest correlation with PM mass and OC. Conclusions: Contrasts in OP between sites, differences in size fractions and correlation with PM composition depended on the specific OP assay used, with OPESR and OPAA showing the most similar results. This suggests that either OPESR or OPAA and OPDTT can complement each other in providing information regarding the oxidative properties of PM, which can subsequently be used to study its health effects. © 2013 The Authors.
view abstract doi: 10.1016/j.scitotenv.2013.11.099 2014 • 136 Parameterized electronic description of carbon cohesion in iron grain boundaries
Hatcher, N. and Madsen, G.K.H. and Drautz, R.
Journal of Physics Condensed Matter 26 (2014)We employ a recently developed iron-carbon orthogonal tight-binding model in calculations of carbon in iron grain boundaries. We use the model to evaluate the properties of carbon near and on the Σ5 (3 1 0)[0 0 1] symmetric tilt grain boundary (GB) in iron, and calculations show that a carbon atom lowers the GB energy by 0.29 eV/atom in accordance with DFT. Carbon segregation to the GB is analyzed, and we find an energy barrier of 0.92 eV for carbon to segregate to the carbon-free interface while segregation to a fully filled interface is disfavored. Local volume (via Voronoi tessellation), magnetic, and electronic effects are correlated with atomic energy changes, and we isolate two different mechanisms governing carbon's behavior in iron: a volumetric strain which increases the energy of carbon in interstitial α iron and a non-strained local bonding which stabilizes carbon at the GB. © 2014 IOP Publishing Ltd.
view abstract doi: 10.1088/0953-8984/26/14/145502 2014 • 135 Particle size effects in the catalytic electroreduction of CO2 on Cu nanoparticles
Reske, R. and Mistry, H. and Behafarid, F. and Roldan Cuenya, B. and Strasser, P.
Journal of the American Chemical Society 136 6978-6986 (2014)A study of particle size effects during the catalytic CO2 electroreduction on size-controlled Cu nanoparticles (NPs) is presented. Cu NP catalysts in the 2-15 nm mean size range were prepared, and their catalytic activity and selectivity during CO2 electroreduction were analyzed and compared to a bulk Cu electrode. A dramatic increase in the catalytic activity and selectivity for H2 and CO was observed with decreasing Cu particle size, in particular, for NPs below 5 nm. Hydrocarbon (methane and ethylene) selectivity was increasingly suppressed for nanoscale Cu surfaces. The size dependence of the surface atomic coordination of model spherical Cu particles was used to rationalize the experimental results. Changes in the population of low-coordinated surface sites and their stronger chemisorption were linked to surging H2 and CO selectivities, higher catalytic activity, and smaller hydrocarbon selectivity. The presented activity-selectivity-size relations provide novel insights in the CO2 electroreduction reaction on nanoscale surfaces. Our smallest nanoparticles (∼2 nm) enter the ab initio computationally accessible size regime, and therefore, the results obtained lend themselves well to density functional theory (DFT) evaluation and reaction mechanism verification. © 2014 American Chemical Society.
view abstract doi: 10.1021/ja500328k 2014 • 134 Polyethylene wear particles induce TLR 2 upregulation in the synovial layer of mice
Paulus, A.C. and Frenzel, J. and Ficklscherer, A. and Roßbach, B.P. and Melcher, C. and Jansson, V. and Utzschneider, S.
Journal of Materials Science: Materials in Medicine 25 507-513 (2014)A cellular and receptor mediated response to ultra-high-molecular-weight- polyethylene (UHMWPE) wear particles results in a release of proinflammatory cytokines and induces an inflammatory reaction causing osteolysis in total joint replacement. This investigation offers insight into the toll-like receptor (TLR) mediated activation by polyethylene wear particles in the synovial layer of mice. We hypothesized that, similar to recent in vitro results, UHMWPE particles lead to an upregulation of TLR 1 and 2 and TLR 4 in vivo in the synovial tissue of mice as well. Therefore, UHMWPE particles were generated in a common knee simulator according to the ISO standard, separated by acid digestion and determined by scanning electron microscopy. Endotoxin was removed using a method based on ultracentrifugation. A particle suspension (50 μl; 0.1 vol./vol.%) was injected into the left knee joint of female Balb/c mice (n = 8). In a control group, phosphate-buffered saline was injected into the left knee of Balb/c mice (n = 8). The mice were sacrificed after 7 days. Immunohistochemical staining was performed with TLR 1, 2 and 4 polyclonal antibodies for Balb/c mice and evaluated by light microscopy. The particle-stimulated group showed a thickened synovial layer, an increased cellular infiltration and a TLR 2-upregulation in the synovial layer compared to the control group. An increased expression of TLR 1 and TLR 4 could not be demonstrated. These results indicate a mainly TLR 2-induced inflammation to polyethylene wear debris in the synovial layer of mice. © 2013 Springer Science+Business Media New York.
view abstract doi: 10.1007/s10856-013-5095-y 2014 • 133 Rational design of gold nanoparticle toxicology assays: A question of exposure scenario, dose and experimental setup
Taylor, U. and Rehbock, C. and Streich, C. and Rath, D. and Barcikowski, S.
Nanomedicine 9 1971-1989 (2014)Many studies have evaluated the toxicity of gold nanoparticles, although reliable predictions based on these results are rare. In order to overcome this problem, this article highlights strategies to improve comparability and standardization of nanotoxicological studies. To this end, it is proposed that we should adapt the nanomaterial to the addressed exposure scenario, using ligand-free nanoparticle references in order to differentiate ligand effects from size effects. Furthermore, surface-weighted particle dosing referenced to the biologically relevant parameter (e.g., cell number or organ mass) is proposed as the gold standard. In addition, it is recommended that we should shift the focus of toxicological experiments from 'live-dead' assays to the assessment of cell function, as this strategy allows observation of bioresponses at lower doses that are more relevant for in vivo scenarios. © 2014 Future Medicine Ltd.
view abstract doi: 10.2217/nnm.14.139 2014 • 132 Redox dynamics of Ni catalysts in CO 2reforming of methane
Mette, K. and Kühl, S. and Tarasov, A. and Düdder, H. and Kähler, K. and Muhler, M. and Schlögl, R. and Behrens, M.
Catalysis Today 101-110 (2014)The influence of redox dynamics of a Ni/MgAl oxide catalyst for dry reforming of methane (DRM) at high temperature was studied to correlate structural stability with catalytic activity and coking propensity. Structural aging of the catalyst was simulated by repeated temperature-programmed reduction/oxidation (TPR/TPO) cycles. Despite a very high Ni loading of 55.4 wt.%, small Ni nanoparticles of 11 nm were obtained from a hydrotalcite-like precursor with a homogeneous distribution. Redox cycling gradually changed the interaction of the active Ni phase with the oxide support resulting in a crystalline Ni/MgAl<inf>2</inf>O<inf>4</inf>-type catalyst. After cycling the average particle size increased from 11 to 21 nm - while still a large fraction of small particles was present - bringing about a decrease in Ni surface area of 72%. Interestingly, the redox dynamics and its strong structural and chemical consequences were found to have only a moderate influence on the activity in DRM at 900 °C, but lead to a stable attenuation of carbon formation due to a lower fraction of graphitic carbon after DRM in a fixed-bed reactor. Supplementary DRM experiments in a thermobalance revealed that coke formation as a continuous process until a carbon limit is reached and confirmed a higher coking rate for the cycled catalyst. © 2014 Published by Elsevier B.V.
view abstract doi: 10.1016/j.cattod.2014.06.011 2014 • 131 Respiratory effects of fine and ultrafine particles from indoor sources-a randomized sham-controlled exposure study of healthy volunteers
Soppa, V.J. and Schins, R.P.F. and Hennig, F. and Hellack, B. and Quass, U. and Kaminski, H. and Kuhlbusch, T.A.J. and Hoffmann, B. and Weinmayr, G.
International Journal of Environmental Research and Public Health 11 6871-6889 (2014)Particulate air pollution is linked to impaired respiratory health. We analyzed particle emissions from common indoor sources (candles burning (CB), toasting bread (TB), frying sausages (FS)) and lung function in 55 healthy volunteers (mean age 33.0 years) in a randomized cross-over controlled exposure study. Lung-deposited particle surface area concentration (PSC), size-specific particle number concentration (PNC) up to 10 μm, and particle mass concentration (PMC) of PM1, PM2.5 and PM10 were determined during exposure (2 h). FEV1, FVC and MEF25%-75% was measured before, 4 h and 24 h after exposure. Wilcoxon-rank sum tests (comparing exposure scenarios) and mixed linear regression using particle concentrations and adjusting for personal characteristics, travel time and transportation means before exposure sessions were performed. While no effect was seen comparing the exposure scenarios and in the unadjusted model, inverse associations were found for PMC from CB and FS in relation to FEV1 and MEF25%-75%. with a change in 10 μg/m3 in PM2.5 from CB being associated with a change in FEV1 of -19 mL (95%-confidence interval-43; 5) after 4 h. PMC from TB and PNC of UFP were not associated with lung function changes, but PSC from CB was. Elevated indoor fine particles from certain sources may be associated with small decreases in lung function in healthy adults. © 2014 by the authors; licensee MDPI, Basel, Switzerland.
view abstract doi: 10.3390/ijerph110706871 2014 • 130 Single core-shell nanoparticle probes for non-invasive magnetic force microscopy
Uhlig, T. and Wiedwald, U. and Seidenstücker, A. and Ziemann, P. and Eng, L.M.
Nanotechnology 25 (2014)We present an easy, fast and reliable method for the preparation of magnetic force microscopy (MFM) probes based on single Co nanoparticles (NPs). Due to their dipolar character, these magnetic probes open up a new approach for quantitative and non-invasive MFM measurements on the nanometer length scale. To guarantee long-term stability of these tips under ambient conditions, an ultrathin protecting Au shell was grown around the Co NPs through photochemical deposition. Single magnetic particles were firmly attached to standard silicon AFM tips using bifunctional self-assembling molecules. Such probes were tested on longitudinal magnetic recording media and compared to the results as recorded with conventional thin-film MFM tips. Easy data interpretation of the magnetic nanoparticle probes in a point dipole model is shown. Our nanoparticle tips provide excellent endurance for MFM recording, enable non-invasive probing while maintaining a high sensitivity, resolution, and reproducibility. © 2014 IOP Publishing Ltd.
view abstract doi: 10.1088/0957-4484/25/25/255501 2014 • 129 Spheronization process particle kinematics determined by discrete element simulations and particle image velocimentry measurements
Koester, M. and García, R.E. and Thommes, M.
International Journal of Pharmaceutics 477 81-87 (2014)Spheronization is an important pharmaceutical manufacturing technique to produce spherical agglomerates of 0.5-2 mm diameter. These pellets have a narrow size distribution and a spherical shape. During the spheronization process, the extruded cylindrical strands break in short cylinders and evolve from a cylindrical to a spherical state by deformation and attrition/agglomeration mechanisms. Using the discrete element method, an integrated modeling-experimental framework is presented, that captures the particle motion during the spheronization process. Simulations were directly compared and validated against particle image velocimetry (PIV) experiments with monodisperse spherical and dry γ-Al2O3 particles. Result demonstrate a characteristic torus like flow pattern, with particle velocities about three times slower than the rotation speed of the friction plate. Five characteristic zones controlling the spheronization process are identified: Zone I, where particles undergo shear forces that favors attrition and contributes material to the agglomeration process; Zone II, where the static wall contributes to the mass exchange between particles; Zone III, where gravitational forces combined with particle motion induce particles to collide with the moving plate and re-enter Zone I; Zone IV, where a subpopulation of particles are ejected into the air when in contact with the friction plate structure; and Zone V where the low poloidal velocity favors a stagnant particle population and is entirely controlled by the batch size. These new insights in to the particle motion are leading to deeper process understanding, e.g., the effect of load and rotation speed to the pellet formation kinetics. This could be beneficial for the optimization of a manufacturing process as well as for the development of new formulations. © 2014 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.ijpharm.2014.10.007 2014 • 128 Structural evolution of silver nanoparticles during wet-chemical synthesis
Banerjee, S. and Loza, K. and Meyer-Zaika, W. and Prymak, O. and Epple, M.
Chemistry of Materials 26 951-957 (2014)The formation of silver nanoparticles during the reduction with glucose in the presence of poly(N-vinyl pyrrolidone) as capping agent was followed for more than 3000 min. First, spherical silver nanoparticles are formed, but in later stages, an increasing fraction of nanotriangles and also a few nanorods develop. Both spherical and trigonal nanoparticles grow with time, indicating separate nucleation pathways. The domain size in the spherical nanoparticles increases proportionally to the particle diameter and is always about 1/ 4 of the diameter, indicating that twinned seeds are formed very early in the process and then simply grow by extending their domains. The lattice constant of the nanoparticles is systematically increased in comparison to microcrystalline silver (4.0877 vs 4.08635 Å) but did not change as a function of particle diameter. A thorough analysis of the texture coefficient, supported by transmission electron microscopy data, showed that the apparently spherical particles are in fact flattened pentagonal prisms, which typically lie on their flat pentagonal face. Neither the presence of oxygen nor the presence of ambient light had any influence on the particle properties. © 2014 American Chemical Society.
view abstract doi: 10.1021/cm4025342 2014 • 127 Surface functionalization of microwave plasma-synthesized silica nanoparticles for enhancing the stability of dispersions
Sehlleier, Y.H. and Abdali, A. and Schnurre, S.M. and Wiggers, H. and Schulz, C.
Journal of Nanoparticle Research 16 (2014)Gas phase-synthesized silica nanoparticles were functionalized with three different silane coupling agents (SCAs) including amine, amine/phosphonate and octyltriethoxy functional groups and the stability of dispersions in polar and non-polar dispersing media such as water, ethanol, methanol, chloroform, benzene, and toluene was studied. Fourier transform infrared spectroscopy showed that all three SCAs are chemically attached to the surface of silica nanoparticles. Amine-functionalized particles using steric dispersion stabilization alone showed limited stability. Thus, an additional SCA with sufficiently long hydrocarbon chains and strong positively charged phosphonate groups was introduced in order to achieve electrosteric stabilization. Steric stabilization was successful with hydrophobic octyltriethoxy-functionalized silica nanoparticles in non-polar solvents. The results from dynamic light scattering measurements showed that in dispersions of amine/phosphonate- and octyltriethoxy-functionalized silica particles are dispersed on a primary particle level. Stable dispersions were successfully prepared from initially agglomerated nanoparticles synthesized in a microwave plasma reactor by designing the surface functionalization. © 2014 Springer Science+Business Media.
view abstract doi: 10.1007/s11051-014-2557-1 2014 • 126 Synthesis of a cementitious material nanocement using bottom-up nanotechnology concept: An alternative approach to avoid COemission during production of cement
Jo, B.W. and Chakraborty, S. and Yoon, K.W.
Journal of Nanomaterials 2014 (2014)The world's increasing need is to develop smart and sustainable construction material, which will generate minimal climate changing gas during their production. The bottom-up nanotechnology has established itself as a promising alternative technique for the production of the cementitious material. The present investigation deals with the chemical synthesis of cementitious material using nanosilica, sodium aluminate, sodium hydroxide, and calcium nitrate as reacting phases. The characteristic properties of the chemically synthesized nanocement were verified by the chemical composition analysis, setting time measurement, particle size distribution, fineness analysis, and SEM and XRD analyses. Finally, the performance of the nanocement was ensured by the fabrication and characterization of the nanocement based mortar. Comparing the results with the commercially available cement product, it is demonstrated that the chemically synthesized nanocement not only shows better physical and mechanical performance, but also brings several encouraging impacts to the society, including the reduction of COemission and the development of sustainable construction material. A plausible reaction scheme has been proposed to explain the synthesis and the overall performances of the nanocement. © 2014 Byung Wan Jo et al.
view abstract doi: 10.1155/2014/409380 2014 • 125 Transversal bed motion in rotating drums using spherical particles: Comparison of experiments with DEM simulations
Komossa, H. and Wirtz, S. and Scherer, V. and Herz, F. and Specht, E.
Powder Technology 264 96-104 (2014)Experimental investigations and numerical simulations with the discrete element method (DEM) were carried out to improve the understanding of the movement and mechanical interaction of particles in rotary kilns. The focus is on the bed movement in the rolling motion mode with rotational speeds varying between 3 and 15. rpm. Characteristic parameters for this system are the Froude number, the dynamic angle of repose, the thickness of the active layer and the particle velocity on the bed surface and at the wall. These parameters were measured in rotating drum experiments, computed in DEM simulations and compared with each other. When available, analytical and/or semi-empirical macroscopic models were included in the comparison. Both the DEM simulations and the analytical macroscopic models show good agreement with the experiments in general. The wide range of parameters considered, like drum diameter, particle diameter and rotational speeds, provide a comprehensive reference data set. © 2014 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2014.05.021 2014 • 124 Viral potassium channels as a robust model system for studies of membrane-protein interaction
Braun, C.J. and Lachnit, C. and Becker, P. and Henkes, L.M. and Arrigoni, C. and Kast, S.M. and Moroni, A. and Thiel, G. and Schroeder, I.
Biochimica et Biophysica Acta - Biomembranes 1838 1096-1103 (2014)The viral channel KcvNTS belongs to the smallest K+ channels known so far. A monomer of a functional homotetramer contains only 82 amino acids. As a consequence of the small size the protein is almost fully submerged into the membrane. This suggests that the channel is presumably sensitive to its lipid environment. Here we perform a comparative analysis for the function of the channel protein embedded in three different membrane environments. 1. Single-channel currents of KcvNTS were recorded with the patch clamp method on the plasma membrane of HEK293 cells. 2. They were also measured after reconstitution of recombinant channel protein into classical planar lipid bilayers and 3. into horizontal bilayers derived from giant unilamellar vesicles (GUVs). The recombinant channel protein was either expressed and purified from Pichia pastoris or from a cell-free expression system; for the latter a new approach with nanolipoprotein particles was used. The data show that single-channel activity can be recorded under all experimental conditions. The main functional features of the channel like a large single-channel conductance (80 pS), high open-probability (> 50%) and the approximate duration of open and closed dwell times are maintained in all experimental systems. An apparent difference between the approaches was only observed with respect to the unitary conductance, which was ca. 35% lower in HEK293 cells than in the other systems. The reason for this might be explained by the fact that the channel is tagged by GFP when expressed in HEK293 cells. Collectively the data demonstrate that the small viral channel exhibits a robust function in different experimental systems. This justifies an extrapolation of functional data from these systems to the potential performance of the channel in the virus/host interaction. This article is part of a Special Issue entitled: Viral Membrane Proteins - Channels for Cellular Networking. © 2013 Elsevier B.V.
view abstract doi: 10.1016/j.bbamem.2013.06.010 2014 • 123 ZnO-modified hybrid polymers as an antibacterial finish for textiles
Farouk, A. and Moussa, S. and Ulbricht, M. and Schollmeyer, E. and Textor, T.
Textile Research Journal 84 40-51 (2014)The antibacterial activity of ZnO is reported by several authors. We present the preparation and application of inorganic–organic hybrid polymers modified/filled with ZnO nanoparticles of varying particle sizes. Inorganic–organic hybrid polymers employed here are based on 3-glycidyloxypropyltrimethoxysilane (GPTMS). ZnO is prepared by hydrolysis of zinc acetate in different solvents (methanol, ethanol or 2-propanol) using lithium hydroxide (LiOH ċ H2O). The hybrid materials prepared are applied to cotton (100%) and cotton/polyester (65/35%) fabrics. The antibacterial performance of these sol-gel derived hybrid materials is exemplarily investigated against Gram-negative bacterium Escherichia coli and Gram–positive Micrococcus luteus. Effects of particle size and concentration for the antibacterial performance are examined. Literature discusses various (active) species and processes responsible for the antibacterial action of ZnO. Therefore, particular attention is paid to investigate active species available in the described systems as well as to observe possible interaction between the nanoparticles and bacteria; the first results are presented. © 2014, SAGE Publications. All rights reserved.
view abstract doi: 10.1177/0040517513485623 2013 • 122 Adhesion, Vitality and Osteogenic Differentiation Capacity of Adipose Derived Stem Cells Seeded on Nitinol Nanoparticle Coatings
Strauß, S. and Neumeister, A. and Barcikowski, S. and Kracht, D. and Kuhbier, J.W. and Radtke, C. and Reimers, K. and Vogt, P.M.
PLoS ONE 8 (2013)Autologous cells can be used for a bioactivation of osteoimplants to enhance osseointegration. In this regard, adipose derived stem cells (ASCs) offer interesting perspectives in implantology because they are fast and easy to isolate. However, not all materials licensed for bone implants are equally suited for cell adhesion. Surface modifications are under investigation to promote cytocompatibility and cell growth. The presented study focused on influences of a Nitinol-nanoparticle coating on ASCs. Possible toxic effects as well as influences on the osteogenic differentiation potential of ASCs were evaluated by viability assays, scanning electron microscopy, immunofluorescence and alizarin red staining. It was previously shown that Nitinol-nanoparticles exert no cell toxic effects to ASCs either in soluble form or as surface coating. Here we could demonstrate that a Nitinol-nanoparticle surface coating enhances cell adherence and growth on Nitinol-surfaces. No negative influence on the osteogenic differentiation was observed. Nitinol-nanoparticle coatings offer new possibilities in implantology research regarding bioactivation by autologous ASCs, respectively enhancement of surface attraction to cells. © 2013 Strauß et al.
view abstract doi: 10.1371/journal.pone.0053309 2013 • 121 Adjustment and online determination of primary particle size in transferred arc synthesis of copper nanoparticles
Stein, M. and Kiesler, D. and Kruis, F.E.
Aerosol Science and Technology 47 1276-1284 (2013)Scaling up metal nanoparticle production is a desired goal of much research, the need of the industry due to the growing market of applications increases significantly. However, a scale up of production rate often leads to an increase in particle size and a broadening of size distribution. Particle characterization in terms of size is mostly done after synthesis. In this work, a transferred arc process is optimized to increase the production rate of pure copper nanoparticles economically. The maximum production rate for different particle sizes is determined by TEOM measurements. While the influence of different carrier gases has been investigated before, different mixtures of nitrogen and argon as carrier gas are used to manipulate the primary particle size. Primary particle size determination is performed by a novel analysis method based on parallel online ELPI and SMPS measurement. An equation is found to calculate the mass mobility exponent directly on the basis of the effective density of an agglomerate. Hence, the method is suitable for determining the primary particle sizes directly online. Copyright © American Association for Aerosol Research.
view abstract doi: 10.1080/02786826.2013.835484 2013 • 120 Advanced nanoparticle generation and excitation by lasers in liquids
Barcikowski, S. and Compagnini, G.
Physical Chemistry Chemical Physics 15 3022-3026 (2013)Today, nanoparticles are widely implemented as functional elements onto surfaces, into volumes and as nano-hybrids, resulting for example in bioactive composites and biomolecule conjugates. However, only limited varieties of materials compatible for integration into advanced functional materials are available: nanoparticles synthesized using conventional gas phase processes are often agglomerated into micro powders that are hard to re-disperse into functional matrices. Chemical synthesis methods often lead to impurities of the nanoparticle colloids caused by additives and precursor reaction products. In the last decade, laser ablation and nanoparticle generation in liquids has proven to be a unique and efficient technique to generate, excite, fragment, and conjugate a large variety of nanostructures in a scalable and clean manner. This editorial briefly highlights selected recent advancements and critical aspects in the field of pulsed laser-based nanoparticle generation and manipulation, including exemplary strategies to harvest the unique properties of the laser-generated nanomaterials in the field of biomedicine and catalysis. The presented critical aspects address future assignments such as size control and scale-up. This journal is © 2013 the Owner Societies.
view abstract doi: 10.1039/c2cp90132c 2013 • 119 Analysis of particle kinematics in spheronization via particle image velocimetry
Koester, M. and Thommes, M.
European Journal of Pharmaceutics and Biopharmaceutics 83 307-314 (2013)Spheronization is a wide spread technique in pellet production for many pharmaceutical applications. Pellets produced by spheronization are characterized by a particularly spherical shape and narrow size distribution. The particle kinematic during spheronization is currently not well-understood. Therefore, particle image velocimetry (PIV) was implemented in the spheronization process to visualize the particle movement and to identify flow patterns, in order to explain the influence of various process parameters. The spheronization process of a common formulation was recorded with a high-speed camera, and the images were processed using particle image velocimetry software. A crosscorrelation approach was chosen to determine the particle velocity at the surface of the pellet bulk. Formulation and process parameters were varied systematically, and their influence on the particle velocity was investigated. The particle stream shows a torus-like shape with a twisted rope-like motion. It is remarkable that the overall particle velocity is approximately 10-fold lower than the tip speed of the friction plate. The velocity of the particle stream can be correlated to the water content of the pellets and the load of the spheronizer, while the rotation speed was not relevant. In conclusion, PIV was successfully applied to the spheronization process, and new insights into the particle velocity were obtained. © 2012 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.ejpb.2012.08.013 2013 • 118 Buoyancy induced limits for nanoparticle synthesis experiments in horizontal premixed low-pressure flat-flame reactors
Weise, C. and Faccinetto, A. and Kluge, S. and Kasper, T. and Wiggers, H. and Schulz, C. and Wlokas, I. and Kempf, A.
Combustion Theory and Modelling 17 504-521 (2013)Premixed low-pressure flat-flame reactors can be used to investigate the synthesis of nanoparticles. The present work examines the flow field inside such a reactor during the formation of carbon (soot) and iron oxide (from Fe(CO)5) nanoparticles, and how it affects the measurements of nanoparticle size distribution. The symmetry of the flow and the impact of buoyancy were analysed by three-dimensional simulations and the nanoparticle size distribution was obtained by particle mass spectrometry (PMS) via molecular beam sampling at different distances from the burner. The PMS measurements showed a striking, sudden increase in particle size at a critical distance from the burner, which could be explained by the flow field predicted in the simulations. The simulation results illustrate different fluid mechanical phenomena which have caused this sudden rise in the measured particle growth. Up to the critical distance, buoyancy does not affect the flow, and an (almost) linear growth is observed in the PMS experiments. Downstream of this critical distance, buoyancy deflects the hot gas stream and leads to an asymmetric flow field with strong recirculation. These recirculation zones increase the particle residence time, inducing very large particle sizes as measured by PMS. This deviation from the assumed symmetric, one-dimensional flow field prevents the correct interpretation of the PMS results. To overcome this problem, modifications to the reactor were investigated; their suitability to reduce the flow asymmetry was analysed. Furthermore, 'safe' operating conditions were identified for which accurate measurements are feasible in premixed low-pressure flat-flame reactors that are transferrable to other experiments in this type of reactor. The present work supports experimentalists to find the best setup and operating conditions for their purpose. © 2013 Copyright Taylor and Francis Group, LLC.
view abstract doi: 10.1080/13647830.2013.781224 2013 • 117 Comparability of mobility particle sizers and diffusion chargers
Kaminski, H. and Kuhlbusch, T.A.J. and Rath, S. and Götz, U. and Sprenger, M. and Wels, D. and Polloczek, J. and Bachmann, V. and Dziurowitz, N. and Kiesling, H.-J. and Schwiegelshohn, A. and Monz, C. and Dahmann, D. and Asbach, C.
Journal of Aerosol Science 57 156-178 (2013)A large study on the comparability of various aerosol instruments was conducted. The study involved altogether 24 instruments, including eleven scanning, sequential and fast mobility particle sizers (five Grimm SMPS+C, three TSI SMPS and three FMPS) with different settings and differential mobility analyzers (DMAs), twelve instruments based on unipolar diffusion charging to determine size integrated concentrations and in some cases mean particle size (five miniDiSCs of the University of Applied Sciences and Arts Northwestern Switzerland, four Philips Aerasense nanoTracers, two TSI Nanoparticle Surface Area Monitors and one Grimm nanoCheck) and one TSI ultrafine condensation particle counter (UCPC). All instruments were simultaneously challenged with particles of various sizes, concentrations and morphologies. All measurement results were compared with those from a freshly calibrated SMPS for size distributions and the UCPC for number concentration. In general, all SMPSs showed good comparability with particularly the sizing agreeing to within a few percent. Differences in the determined number concentration were somewhat more pronounced, but the largest deviations could be tracked back to the use of an older software version. The comparability of the FMPSs was shown to be lower, with discrepancies on the order of ±25% for sizing and ±30% for total concentrations. The discrepancies between FMPSs and the internal reference SMPS seemed to be influenced by particle size and morphology. Total number and/or lung deposited surface area concentrations measured with unipolar diffusion charger based instruments generally agreed to within ±30% with the internal references (CPC for number concentrations; lung deposited surface area derived from SMPS measurements), as long as the particle size distributions of the test aerosols were within the specified limits for the instruments. When the upper size limit was exceeded, deviations of up to several hundred percent were detected. © 2012 Elsevier Ltd.
view abstract doi: 10.1016/j.jaerosci.2012.10.008 2013 • 116 Coupled DEM/CFD simulation of heat transfer in a generic grate system agitated by bars
Rickelt, S. and Sudbrock, F. and Wirtz, S. and Scherer, V.
Powder Technology 249 360-372 (2013)Coupled DEM/CFD simulations are compared to experiments with agitated spherical particles (10. mm in diameter) on a generic grate and exposed to a transient heat-up by a hot air flow. A video camera and a thermographic system monitor the experiments. Because the particles show Biot numbers >. 1 the radial temperature distribution within the particle has been calculated by solving the unsteady one-dimensional differential equation for heat conduction in the DEM simulations. A visual comparison of the heat-up of the particles and particle transport within the bed shows a good agreement between simulations and experiments. In addition, local minimum, maximum and average particle surface temperatures in different layers of the particle bed are calculated. Experimentally measured temperature gradients over the particle bed height are in very good agreement to DEM/CFD simulations. © 2013 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2013.08.043 2013 • 115 Design and experimental evaluation of a new nanoparticle thermophoretic personal sampler
Azong-Wara, N. and Asbach, C. and Stahlmecke, B. and Fissan, H. and Kaminski, H. and Plitzko, S. and Bathen, D. and Kuhlbusch, T.A.J.
Journal of Nanoparticle Research 15 (2013)A personal sampler that thermophoretically samples particles between a few nanometers and approximately 300 nm has been designed and first prototypes built. The thermal precipitator (TP) is designed to take samples in the breathing zone of a worker in order to determine the personal exposure to airborne nanomaterials. In the sampler, particles are deposited onto silicon substrates that can be used for consecutive electron microscopic (EM) analysis of the particle size distribution and chemical composition of the sampled particles. Due to very homogeneous size-independent particle deposition on a large portion of the substrate, representative samples can be taken for offline analysis. The experimental evaluation revealed a good general agreement with numerical simulations concerning homogeneity of the deposit and a very high correlation (R^2 = 0.98) of the deposition rate per unit area with number concentrations simultaneously measured with an SMPS for particle sizes between 14 and 305 nm. The samplers' small size of only 45 x 32 × 97 mm3 and low weight of only 140 g make it perfectly suitable as a personal sampler. The power consumption for temperature control and pump is around 1.5 W and can be easily provided by batteries. © 2013 Springer Science+Business Media Dordrecht.
view abstract doi: 10.1007/s11051-013-1530-8 2013 • 114 Design of biorelevant test setups for the prediction of diclofenac in vivo features after oral administration
Guhmann, M. and Thommes, M. and Gerber, F. and Pöllinger, N. and Klein, S. and Breitkreutz, J. and Weitschies, W.
Pharmaceutical Research 30 1483-1501 (2013)Purpose: Design of biorelevant test setups mimicking the physiological conditions experienced by drugs after oral administration along the passage through the mouth and the GI tract for the in vitro evaluation of diclofenac exhibiting multiple-peak phenomenon during absorption. Methods: The biorelevant models simulated successively saliva (SSF, pH 6.2-6.75-7.4, 5 mL, 3 min), gastric (SGF-FaSSGF, pH 1.2-1.6, 50-250 mL, 30 min) and intestinal (FaSSIF, pH 6.8, 250 mL, 60 min) fluids. Applying these models, diclofenac free acid and its sodium/potassium salt were comparatively evaluated for dissolution and further characterized by HPLC, optical morphogranulometry, DSC and PXRD to elucidate peculiar behaviors. Results: Diclofenac salts almost completely dissolved in SSF and showed a transitional dissolution pattern before complete precipitation in SGF/FaSSGF. This peculiar pattern correlated with simultaneous chemical modification and formation of agglomerates. With low dissolution in SSF and almost immediately complete precipitation, these behaviors were not observed with diclofenac free acid. Distinct diclofenac features were strongly determined by pH-modifications after oral administration. Conclusions: The multiple-peak phenomenon observed after administrating a solution, suspension or dispersible formulation of diclofenac salts are likely caused by drug precipitation and agglomeration in the stomach leading to irregular gastric-emptying. Diclofenac free acid may provide more reliable in vivo features. © 2013 Springer Science+Business Media New York.
view abstract doi: 10.1007/s11095-013-0974-y 2013 • 113 Direct gas-phase synthesis of single-phase β-FeSi2 nanoparticles
Bywalez, R. and Orthner, H. and Mehmedovic, E. and Imlau, R. and Kovacs, A. and Luysberg, M. and Wiggers, H.
Journal of Nanoparticle Research 15 (2013)For the first time, phase-pure β-FeSi2 nanoparticles were successfully produced by gas-phase synthesis. We present a method to fabricate larger quantities of semiconducting β-FeSi2 nanoparticles, with crystallite sizes between 10 and 30 nm, for solar and thermoelectric applications utilizing a hot-wall reactor. A general outline for the production of those particles by thermal decomposition of silane and iron pentacarbonyl is provided based on kinetic data. The synthesized particles are investigated by X-ray diffraction and transmission electron microscopy, providing evidence that the as-prepared materials are indeed β-FeSi2, while revealing morphological characteristics inherent to the nanoparticles created. © 2013 Springer Science+Business Media.
view abstract doi: 10.1007/s11051-013-1878-9 2013 • 112 Effect of carrier gas composition on transferred arc metal nanoparticle synthesis
Stein, M. and Kiesler, D. and Kruis, F.E.
Journal of Nanoparticle Research 15 (2013)Metal nanoparticles are used in a great number of applications; an effective and economical production scaling-up is hence desirable. A simple and cost-effective transferred arc process is developed, which produces pure metal (Zn, Cu, and Ag) nanoparticles with high production rates, while allowing fast optimization based on energy efficiency. Different carrier gas compositions, as well as the electrode arrangements and the power input are investigated to improve the production and its efficiency and to understand the arc production behavior. The production rates are determined by a novel process monitoring method, which combines an online microbalance method with a scanning mobility particle sizer for fast production rate and size distribution measurement. Particle characterization is performed via scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction measurements. It is found that the carrier gas composition has the largest impact on the particle production rate and can increase it with orders of magnitude. This appears to be not only a result of the increased heat flux and melt temperature but also of the formation of tiny nitrogen (hydrogen) bubbles in the molten feedstock, which impacts feedstock evaporation significantly in bi-atomic gases. A production rate of sub 200 nm particles from 20 up to 2,500 mg/h has been realized for the different metals. In this production range, specific power consumptions as low as 0.08 kWh/g have been reached. © 2013 Springer Science+Business Media Dordrecht.
view abstract doi: 10.1007/s11051-012-1400-9 2013 • 111 Effect of particle size on ferroelectric and magnetic properties of BiFeO3 nanopowders
Castillo, M.E. and Shvartsman, V.V. and Gobeljic, D. and Gao, Y. and Landers, J. and Wende, H. and Lupascu, D.C.
Nanotechnology 24 (2013)The ferroelectric and magnetic behaviour of multiferroic BiFeO3 nanoparticles has been studied using piezoresponse force microscopy (PFM), Mössbauer spectroscopy and SQUID magnetometry. The results of the PFM studies indicate a decay of the spontaneous polarization with decreasing particle size. Nevertheless, particles with diameter ∼50 nm still manifest ferroelectric behaviour. At the same time these particles are weakly ferromagnetic. The Mössbauer spectroscopy studies prove that the weak ferromagnetic state is due to non-compensated surface spins rather than distortions of the cycloidal spin structure characteristic for bulk BiFeO 3. © 2013 IOP Publishing Ltd.
view abstract doi: 10.1088/0957-4484/24/35/355701 2013 • 110 Experimental and numerical investigation on the influence of particle shape and shape approximation on hopper discharge using the discrete element method
Höhner, D. and Wirtz, S. and Scherer, V.
Powder Technology 235 614-627 (2013)In this study experimental and numerical investigations with the discrete element method (DEM) on the discharge of spheres and polyhedral dices from a hopper are conducted. In DEM the dices are approximated by polyhedra and smoothed polyhedra respectively and hence allow examining the influence of sharply-edged and smooth particle geometries on the discharge properties. Simulation results are in good general agreement with the experiments and hence demonstrate the adequacy of DEM as well as polyhedral and smoothed polyhedral approximation schemes to simulate non-spherical particle geometries. Compared to spheres the dices exhibit an increased flow resistance and readiness to form pile-ups at the bottom walls of the hopper. Both phenomena are better approximated using polyhedral approximations of the dices, showcasing the influence of the selected shape approximation scheme on the numerical results. © 2012 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2012.11.004 2013 • 109 Facile synthesis of polymer core@silver shell hybrid nanoparticles with super surface enhanced Raman scattering capability
Huo, D. and He, J. and Yang, S. and Zhou, Z. and Hu, Y. and Epple, M.
Journal of Colloid and Interface Science 393 119-125 (2013)Silver nano-shells (SNSs) were synthesized via a two-step seeds-mediated method. Polymer cores were composed of ultrafine gold nanoparticles (NPs) modified chitosan-poly(acrylic acid) nanoparticles (CS-PAA NPs). Then, deposition of silver upon gold nucleus leads to the seed enlargement and finally forms silver shell on the surface of CS-PAA NPs to get SNSs. Transmission electron microscope (TEM) showed SNSs had a discrete silver shell plus some pores and gaps, which could acted as "hot spots" and provided the great potential of these SNSs to be used as SERS substrates with wavelength ranging from visible to infrared region (700-1000. nm) by tuning shell coverage of silver. SERS experiments with dibenzyl disulphide (DBDS) as the indicator showed that the resulting SNSs allowed the production of highly consistent enhancement of the Raman signals down to nM concentrations of DBDS. Considering the excellent biocompatibility of polymer core and their small size, these SNSs are highly desirable candidates as the enhancers for high performance SERS analysis and as SERS optical labels in biomedical imaging. © 2012 Elsevier Inc.
view abstract doi: 10.1016/j.jcis.2012.11.003 2013 • 108 Guided hierarchical co-assembly of soft patchy nanoparticles
Gröschel, A.H. and Walther, A. and Löbling, T.I. and Schacher, F.H. and Schmalz, H. and Müller, A.H.E.
Nature 503 247-251 (2013)The concept of hierarchical bottom-up structuring commonly encountered in natural materials provides inspiration for the design of complex artificial materials with advanced functionalities. Natural processes have achieved the orchestration of multicomponent systems across many length scales with very high precision, but man-made self-assemblies still face obstacles in realizing well-defined hierarchical structures. In particle-based self-assembly, the challenge is to program symmetries and periodicities of superstructures by providing monodisperse building blocks with suitable shape anisotropy or anisotropic interaction patterns ('patches'). Irregularities in particle architecture are intolerable because they generate defects that amplify throughout the hierarchical levels. For patchy microscopic hard colloids, this challenge has been approached by using top-down methods (such as metal shading or microcontact printing), enabling molecule-like directionality during aggregation. However, both top-down procedures and particulate systems based on molecular assembly struggle to fabricate patchy particles controllably in the desired size regime (10-100 nm). Here we introduce the co-assembly of dynamic patchy nanoparticles-that is, soft patchy nanoparticles that are intrinsically self-assembled and monodisperse-as a modular approach for producing well-ordered binary and ternary supracolloidal hierarchical assemblies. We bridge up to three hierarchical levels by guiding triblock terpolymers (length scale ∼10 nm) to form soft patchy nanoparticles (20-50 nm) of different symmetries that, in combination, co-assemble into substructured, compartmentalized materials (>10 μm) with predictable and tunable nanoscale periodicities. We establish how molecular control over polymer composition programs the building block symmetries and regulates particle positioning, offering a route to well-ordered mixed mesostructures of high complexity. © 2013 Macmillan Publishers Limited. All rights reserved.
view abstract doi: 10.1038/nature12610 2013 • 107 Influence of janus particle shape on their interfacial behavior at liquid-liquid interfaces
Ruhland, T.M. and Gröschel, A.H. and Ballard, N. and Skelhon, T.S. and Walther, A. and Müller, A.H.E. and Bon, S.A.F.
Langmuir 29 1388-1394 (2013)We investigate the self-Assembly behavior of Janus particles with different geometries at a liquid-liquid interface. The Janus particles we focus on are characterized by a phase separation along their major axis into two hemicylinders of different wettability. We present a combination of experimental and simulation data together with detailed studies elucidating the mechanisms governing the adsorption process of Janus spheres, Janus cylinders, and Janus discs. Using the pendant drop technique, we monitor the assembly kinetics following changes in the interfacial tension of nanoparticle adsorption. According to the evolution of the interfacial tension and simulation data, we will specify the characteristics of early to late stages of the Janus particle adsorption and discuss the effect of Janus particle shape and geometry. The adsorption is characterized by three adsorption stages which are based on the different assembly kinetics and different adsorption mechanisms depending on the particle shape. © 2013 American Chemical Society.
view abstract doi: 10.1021/la3048642 2013 • 106 Influence of MCC II fraction and storage conditions on pellet properties
Krueger, C. and Thommes, M. and Kleinebudde, P.
European Journal of Pharmaceutics and Biopharmaceutics 85 1039-1045 (2013)Microcrystalline cellulose II (MCC II) - a polymorph of commonly used MCC I - was introduced as new pelletization aid in wet-extrusion/spheronization leading to fast disintegrating pellets. Previous investigations suggested that pellet properties were influenced by the fraction of MCC II. Furthermore, it is unknown whether the storage conditions can affect the disintegration behavior. Therefore, the effects of MCC II fraction and the storage conditions on several pellet properties were investigated. MCC II-based pellets were prepared of pure MCC II or binary mixtures containing 10-50% (steps of 10%) MCC II as pelletization aid and theophylline, chloramphenicol or lactose. The pellets were characterized by their aspect ratio, equivalent diameter, water content, tensile strength, porosity as well as shrinking, and disintegration behavior and drug release according to their MCC II fraction. Furthermore, the pellets were stored at different relative humidities (0-97%rh), and the influence on their disintegration and drug release was investigated. With increasing MCC II fraction, the pellets became lager in size, decreased their porosity, and required higher water contents for spheronization. Moreover, the disintegration time increased and the disintegration itself was incomplete. Furthermore, the storage conditions had an impact on the disintegration properties of MCC II-based pellets. The disintegrating was affected irreversibly after storage at high humidity (80-97%rh) resulting in a slow drug release. Therefore, MCC II-based pellets need to be stored below 80%rh to secure a fast disintegration. A better knowledge of the properties of MCC II-based pellets was obtained providing a basis for a successful manufacturing and adequate storage of MCC II-based pellets prepared by extrusion/spheronization. © 2013 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.ejpb.2013.07.001 2013 • 105 Influence of the cation alkyl chain length of imidazolium-based room temperature ionic liquids on the dispersibility of TiO2 nanopowders
Wittmar, A. and Gajda, M. and Gautam, D. and Dörfler, U. and Winterer, M. and Ulbricht, M.
Journal of Nanoparticle Research 15 (2013)The influence of the length of the cation alkyl chain on the dispersibility by ultrasonic treatment of TiO2 nanopowders in hydrophilic imidazolium-based room temperature ionic liquids was studied for the first time by dynamic light scattering and advanced rheology. TiO2 nanopowders had been synthesized by chemical vapor synthesis (CVS) under varied conditions leading to two different materials. A commercial nanopowder had been used for comparison. Characterizations had been done using transmission electron microscopy, X-ray diffraction, nitrogen adsorption with BET analysis, and FT-IR spectroscopy. Primary particle sizes were about 6 and 8 nm for the CVS-based and 26 nm for the commercial materials. The particle size distribution in the dispersion was strongly influenced by the length of the cation alkyl chain for all the investigated powders with different structural characteristics and concentrations in the dispersion. It was found that an increase of the alkyl chain length was beneficial, leading to a narrowing of the particle size distribution and a decrease of the agglomerate size in dispersion. The smallest average nanoparticle sizes in dispersion were around 30 nm. Additionally, the surface functionality of the nanoparticles, the concentration of the solid material in the liquid, and the period of ultrasonic treatment control the dispersion quality, especially in the case of the ionic liquids with the shorter alkyl chain. The influence of the nanopowders characteristics on their dispersibility decreases considerably with increasing cation alkyl chain length. The results indicate that ionic liquids with adapted structure are candidates as absorber media for nanoparticles synthesized in gas phase processes to obtain liquid dispersions directly without redispergation. © 2013 Springer Science+Business Media Dordrecht.
view abstract doi: 10.1007/s11051-013-1463-2 2013 • 104 Interaction of electrolyte molecules with carbon materials of well-defined porosity: Characterization by solid-state NMR spectroscopy
Borchardt, L. and Oschatz, M. and Paasch, S. and Kaskel, S. and Brunner, E.
Physical Chemistry Chemical Physics 15 15177-15184 (2013)Electrochemical double-layer capacitors (EDLCs or supercapacitors) are of special potential interest with respect to energy storage. Nearly all EDLCs make use of porous carbons as electrode materials. Further tuning of their performance in EDLC applications requires a better understanding of their properties. In particular, the understanding of the interactions between carbon-based materials and electrolyte solutions is of fundamental interest with respect to future applications. Since the capacitance of carbon-based electrode materials is known to depend on the pore size, we have studied different porous carbon materials of well-defined, variable pore size loaded with 1 M TEABF 4 in acetonitrile or with pure acetonitrile using solid-state magic angle spinning (MAS) 1H, 11B, and 13C NMR spectroscopy. © the Owner Societies 2013.
view abstract doi: 10.1039/c3cp52283k 2013 • 103 Investigations on diffusion limitations of biocatalyzed reactions in amphiphilic polymer conetworks in organic solvents
Schoenfeld, I. and Dech, S. and Ryabenky, B. and Daniel, B. and Glowacki, B. and Ladisch, R. and Tiller, J.C.
Biotechnology and Bioengineering 110 2333-2342 (2013)The use of enzymes as biocatalysts in organic media is an important issue in modern white biotechnology. However, their low activity and stability in those media often limits their full-scale application. Amphiphilic polymer conetworks (APCNs) have been shown to greatly activate entrapped enzymes in organic solvents. Since these nanostructured materials are not porous, the bioactivity of the conetworks is strongly limited by diffusion of substrate and product. The present manuscript describes two different APCNs as nanostructured microparticles, which showed greatly increased activities of entrapped enzymes compared to those of the already activating membranes and larger particles. We demonstrated this on the example of APCN particles based on PHEA-l-PDMS loaded with α-Chymotrypsin, which resulted in an up to 28,000-fold higher activity of the enzyme compared to the enzyme powder. Furthermore, lipase from Rhizomucor miehei entrapped in particles based on PHEA-l-PEtOx was tested in n-heptane, chloroform, and substrate. Specific activities in smaller particles were 10- to 100-fold higher in comparison to the native enzyme. The carrier activity of PHEA-l-PEtOx microparticles was tenfold higher with some 25-50-fold lower enzyme content compared to a commercial product. Biotechnol. Bioeng. 2013; 110:2333-2342. © 2013 Wiley Periodicals, Inc.
view abstract doi: 10.1002/bit.24906 2013 • 102 Label-free SERS monitoring of chemical reactions catalyzed by small gold nanoparticles using 3D plasmonic superstructures
Xie, W. and Walkenfort, B. and Schlücker, S.
Journal of the American Chemical Society 135 1657-1660 (2013)Label-free in situ surface-enhanced Raman scattering (SERS) monitoring of reactions catalyzed by small gold nanoparticles using rationally designed plasmonic superstructures is presented. Catalytic and SERS activities are integrated into a single bifunctional 3D superstructure comprising small gold satellites self-assembled onto a large shell-isolated gold core, which eliminates photocatalytic side reactions. © 2012 American Chemical Society.
view abstract doi: 10.1021/ja309074a 2013 • 101 Long-circulating poly(ethylene glycol)-coated poly(lactid-co-glycolid) microcapsules as potential carriers for intravenously administered drugs
Ferenz, K.B. and Waack, I.N. and Mayer, C. and De Groot, H. and Kirsch, M.
Journal of Microencapsulation 30 632-642 (2013)The intrinsic advantages of microcapsules with regard to nanocapsules as intravenous drug carrier systems are still not fully exploited. Especially, in clinical situations where a long-term drug release within the vascular system is desired, if large amounts of drug have to be administered or if capillary leakage occurs, long-circulating microparticles may display a superior alternative to nanoparticles. Here, microcapsules were synthesised and parameters such as in vitro tendency of agglomeration, protein adsorption and in vivo performance were investigated. Biocompatible poly(ethylene glycol) (PEG)-coated poly(DL-lactide-co-glycolide) (PLGA) as wall material, solid and perfluorodecalin (PFD)-filled PEG-PLGA microcapsules (1.5 μm diameter) were manufactured by using a modified solvent evaporation method with either 1% poly(vinyl alcohol) (PVA) or 1.5% cholate as emulsifying agents. Compared to microcapsules manufactured with cholate, the protein adsorption (albumin and IgG) was clearly decreased and agglomeration of capsules was prevented, when PVA was used. The intravenous administration of these microcapsules, both solid and PFD-filled, in rats was successful and exhibited a circulatory half-life of about 1 h. Our data clearly demonstrate that PEG-PLGA microcapsules, manufactured by using PVA, are suitable biocompatible, long-circulating drug carriers, applicable for intravenous administration. © 2013 Informa UK Ltd. All rights reserved.
view abstract doi: 10.3109/02652048.2013.770098 2013 • 100 Mechanism of the uptake of cationic and anionic calcium phosphate nanoparticles by cells
Sokolova, V. and Kozlova, D. and Knuschke, T. and Buer, J. and Westendorf, A.M. and Epple, M.
Acta Biomaterialia 9 7527-7535 (2013)The uptake of calcium phosphate nanoparticles (diameter 120 nm) with different charge by HeLa cells was studied by flow cytometry. The amount of uptaken nanoparticles increased with increasing concentration of nanoparticles in the cell culture medium. Several inhibitors of endocytosis and macropinocytosis were applied to elucidate the uptake mechanism of nanoparticles into HeLa cells: wortmannin, LY294002, nocodazole, chlorpromazine and nystatin. Wortmannin and LY294002 strongly reduced the uptake of anionic nanoparticles, which indicates macropinocytosis as uptake mechanism. For cationic nanoparticles, the uptake was reduced to a lesser extent, indicating a different uptake mechanism. The localization of nanoparticles inside the cells was investigated by conjugating them with the pH-sensitive dye SNARF-1. The nanoparticles were localized in lysosomes after 3 h of incubation. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
view abstract doi: 10.1016/j.actbio.2013.02.034 2013 • 99 Mutual enhancement of the current density and the coulombic efficiency for a bioanode by entrapping bi-enzymes with Os-complex modified electrodeposition paints
Shao, M. and Nadeem Zafar, M. and Sygmund, C. and Guschin, D.A. and Ludwig, R. and Peterbauer, C.K. and Schuhmann, W. and Gorton, L.
Biosensors and Bioelectronics 40 308-314 (2013)A bioanode with high current density and coulombic efficiency was developed by co-immobilization of pyranose dehydrogenase from Agaricus meleagris (AmPDH) with the dehydrogenase domain of cellobiose dehydrogenase from Corynascus thermophiles (recDH. CtCDH) expressed recombinantly in Escherichia coli. The two enzymes were entrapped in Os-complex modified electrodeposition polymers (Os-EDPs) with specifically adapted redox potential by means of chemical co-deposition. AmPDH oxidizes glucose at both the C2 and C3 positions whereas recDH. CtCDH oxidizes glucose only at the C1 position. Electrochemical measurements reveal that maximally 6 electrons can be harvested from one glucose molecule at the two-enzyme anode via a cascade reaction, as AmPDH oxidizes the products formed from of the recDH. CtCDH catalyzed substrate oxidation and vice versa. Furthermore, a significant increase in current density can be obtained by combining AmPDH and recDH. CtCDH in a single modified electrode. We propose the use of this bioanode in biofuel cells with increased current density and coulombic efficiency. © 2012 Elsevier B.V.
view abstract doi: 10.1016/j.bios.2012.07.069 2013 • 98 Nanoscale thermomechanics of wear-resilient polymeric bilayer systems
Kaule, T. and Zhang, Y. and Emmerling, S. and Pihan, S. and Foerch, R. and Gutmann, J. and Butt, H.-J. and Berger, R. and Duerig, U. and Knoll, A.W.
ACS Nano 7 748-759 (2013)We explore the effect of an ultrathin elastic coating to optimize the mechanical stability of an underlying polymer film for nanoscale applications. The coating consists of a several nanometer thin plasma-polymerized norbornene layer. Scanning probes are used to characterize the system in terms of shear-force-induced wear and thermally assisted indentation. The layer transforms a weakly performing polystyrene film into a highly wear-resistive system, ideal for high-density and low-power data storage applications. The result can be understood from the indentation characteristics with a hot and sharp indenter tip. The latter gives rise to a deformation mode in the fully plastic regime, enabling a simple interpretation of the results. The softening transition and the yield stress of the system on a microsecond time scale and a nanometer size scale were obtained. We show that the plastic deformation is governed by yielding in the polystyrene sublayer, which renders the overall system soft for plastic deformation. The ultrathin protection layer contributes as an elastic skin, which shields part of the temperature and pressure and enables the high wear resistance against lateral forces. Moreover, the method of probing polymers at microsecond and nanometer size scales opens up new opportunities for studying polymer physics in a largely unexplored regime. Thus, we find softening temperatures of more than 100 °C above the polystyrene glass transition, which implies that for the short interaction time scales the glassy state of the polymer is preserved up to this temperature. © 2012 American Chemical Society.
view abstract doi: 10.1021/nn305047m 2013 • 97 Particle size effect in methane activation over supported palladium nanoparticles
Ota, A. and Kunkes, E.L. and Kröhnert, J. and Schmal, M. and Behrens, M.
Applied Catalysis A: General 452 203-213 (2013)A synthesis method for producing MgAl oxide supported uniform palladium nanoparticles with varying diameters has been developed. The method consists of reductive-thermal decomposition of a PdMgAl hydrotalcite-like compound, formed via co-precipitation of metal nitrate salts and sodium carbonate. The hydrotalcite-like precursors were characterized by XRD, TG-MS and SEM, and were found to contain a well-defined crystalline structure and a uniform distribution of all constituent elements. The resulting catalysts were characterized by XRD, TEM, Chemisorption of CO and in situ IR measurements of CO, and were found to consist of partially oxide-embedded Pd nanoparticles with diameters ranging from d = 1.7 to 3.3 nm and correspond dispersions of 67-14%. Furthermore, the particle size was found to be inversely related to Pd loading. The palladium catalysts were studied for methane activation via chemisorption at 200 and 400°C followed by a temperature programmed surface hydrogenation. The most disperse catalyst (d = 1.7 nm) possessed an intrinsic methane adsorption capacity, which was an order of magnitude larger than that of other catalysts in the series, indicating a strong structure sensitivity in this reaction. Additionally, the methane adsorption capacity of the hydrotalcite-derived Pd catalysts was nearly two orders of magnitude higher than that of catalysts derived through other synthesis pathways such as colloidal deposition or sonochemical reduction. © 2012 Elsevier B.V.
view abstract doi: 10.1016/j.apcata.2012.11.021 2013 • 96 Quantitative evaluation of size selective precipitation of Mn-doped ZnS quantum dots by size distributions calculated from UV/Vis absorbance spectra
Segets, D. and Komada, S. and Butz, B. and Spiecker, E. and Mori, Y. and Peukert, W.
Journal of Nanoparticle Research 15 (2013)We demonstrate the quantitative evaluation of the sharp classification of manganese-doped zinc sulfide (ZnS:Mn) quantum dots by size selective precipitation. The particles were characterized by the direct conversion of absorbance spectra to particle size distributions (PSDs) and high-resolution transmission electron micrographs (HRTEM). Gradual addition of a poor solvent (2-propanol) to the aqueous colloid led to the flocculation of larger particles. Though the starting suspension after synthesis had an already narrow PSD between 1.5 and 3.2 nm, different particle size fractions were subsequently isolated by the careful adjustment of the good solvent/poor solvent ratio. Moreover, due to the fact that for the analysis of the classification results the size distributions were available, an in-depth understanding of the quality of the distinct classification steps could be achieved. From the PSDs of the feed, as well as the coarse and the fine fractions with their corresponding yields determined after each classification step, an optimum after the first addition of poor solvent was identified with a maximal separation sharpness κ as high as 0.75. Only by the quantitative evaluation of classification results leading to an in-depth understanding of the relevant driving forces, a future transfer of this lab scale post-processing to larger quantities will be possible. © 2013 Springer Science+Business Media Dordrecht.
view abstract doi: 10.1007/s11051-013-1486-8 2013 • 95 Silver-doped calcium phosphate nanoparticles: Synthesis, characterization, and toxic effects toward mammalian and prokaryotic cells
Peetsch, A. and Greulich, C. and Braun, D. and Stroetges, C. and Rehage, H. and Siebers, B. and Köller, M. and Epple, M.
Colloids and Surfaces B: Biointerfaces 102 724-729 (2013)Spherical silver-doped calcium phosphate nanoparticles were synthesized in a co-precipitation route from calcium nitrate/silver nitrate and ammonium phosphate in a continuous process and colloidally stabilized by carboxymethyl cellulose. Nanoparticles with 0.39wt% silver content and a diameter of about 50-60nm were obtained. The toxic effects toward mammalian and prokaryotic cells were determined by viability tests and determination of the minimal inhibitory and minimal bactericidal concentrations (MIC and MBC). Three mammalian cells lines, i.e. human mesenchymal stem cells (hMSC) and blood peripheral mononuclear cells (PBMC, monocytes and T-lymphocytes), and two prokaryotic strains, i.e. Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were used. Silver-doped calcium phosphate nanoparticles and silver acetate showed similar effect toward mammalian and prokaryotic cells with toxic silver concentrations in the range of 1-3μgmL-1. © 2012 Elsevier B.V.
view abstract doi: 10.1016/j.colsurfb.2012.09.040 2013 • 94 Single gold trimers and 3D superstructures exhibit a polarization- independent SERS response
Steinigeweg, D. and Schütz, M. and Schlücker, S.
Nanoscale 5 110-113 (2013)Dimers of metal nanospheres are well-known for their characteristic anisotropic optical response. Here, we demonstrate in single-particle SERS experiments that individual gold trimers and 3D superstructures exhibit a polarization-independent SERS response. This optical behavior of single particle clusters provides constant SERS signals, independent of the mutual orientation of the incident laser polarization and the plasmonic nanostructure, which is desired or even required in many SERS applications. © 2013 The Royal Society of Chemistry.
view abstract doi: 10.1039/c2nr31982a 2013 • 93 Size control of laser-fabricated surfactant-free gold nanoparticles with highly diluted electrolytes and their subsequent bioconjugation
Rehbock, C. and Merk, V. and Gamrad, L. and Streubel, R. and Barcikowski, S.
Physical Chemistry Chemical Physics 15 3057-3067 (2013)Size control of laser-fabricated surfactant-free gold nanoparticles is a challenging endeavor. In this work, we show that size control can be achieved by adding ions with low salinity during synthesis. In addition, this approach offers the opportunity to fundamentally study ion interactions with bare nanoparticle surfaces and can help to elucidate the nanoparticle formation mechanism. The studies were carried out in a flow-through reactor and in the presence of NaCl, NaBr and sodium phosphate buffer at minimal ionic strengths. A significant size quenching effect at ionic strengths from 1-50 μM was found, which allowed surfactant-free nanoparticle size control with average diameters of 6-30 nm. This effect went along with low polydispersity and minimal aggregation tendencies and was confirmed by UV-vis spectroscopy, TEM, SEM and analytical disk centrifugation. Our findings indicate that size quenching originates from an anionic electrostatic stabilization depending on the nanoparticle surface area, which may be caused by specific ion adsorption. By subsequent delayed bioconjugation in liquid-flow using bovine serum albumin as a stabilizing agent, nano-bioconjugates with good stability in cell culture media were obtained, which are applicable in toxicology and cell biology. This journal is © 2013 the Owner Societies.
view abstract doi: 10.1039/c2cp42641b 2013 • 92 Size resolved particle number emission factors of motorway traffic differentiated between heavy and light duty vehicles
Nickel, C. and Kaminski, H. and Hellack, B. and Quass, U. and John, A. and Klemm, O. and Kuhlbusch, T.A.J.
Aerosol and Air Quality Research 13 450-461 (2013)It is well accepted that airborne particles can induce adverse health effects dependent on the source, composition, morphology and size. Studies indicate that ultrafine particles (diameter< 100 nm) are of specific importance. Therefore, upwind and downwind field measurements of particle number size distributions (14-750 nm), nitrogen oxides, PM10and PM1mass concentrations were performed to derive information on sources of those types of particles from motorways. The measurement stations were located at a motorway in a rural area with flat terrain and unhindered air flow situation. The mean particle number concentration was 20,900 #/cm3downwind and 3,400 #/cm3upwind of the motorway. The highest total particle number concentration at the downwind station was 141,000 #/cm3. About 90% of these particles were< 100 nm. The measured data were used to derive size-dependent emission factors (EF) using the NOxtracer method. This method is based on listed NOxEF (HBEFA, 2010). The average total particle number EF per vehicle was determined to be 3.5 × 1014particles/km. The average particle EF was 2.1 × 1014particles/km and 11.8 × 1014particles/km for light duty vehicles (LDV) and heavy duty vehicles (HDV). The higher EF for HDV is mainly caused by particles with diameters below 50 nm. The comparison of EF from the literature show the importance of the particle size range investigated. Especially particles at the lower size detection limit contribute to total particle number concentrations and hence determine the EF significantly. In the EURO V directive, particle number emission limits of 6 × 1011particles/km were set for diesel passenger cars. This value is defined for non-volatile particles > 23 nm. The EF for the given size range (> 23 nm) determined in this study were significantly higher with 1.0 × 1014for LDV. © Taiwan Association for Aerosol Research.
view abstract doi: 10.4209/aaqr.2012.07.0187 2013 • 91 Solid crystal suspensions containing griseofulvin-Preparation and bioavailability testing
Reitz, E. and Vervaet, C. and Neubert, R.H.H. and Thommes, M.
European Journal of Pharmaceutics and Biopharmaceutics 83 193-202 (2013)The improvement of the bioavailability of poorly soluble drugs has been an important issue in pharmaceutical research for many years. Despite the suggestion of several other technologies in the past, drug particle size reduction is still an appropriate strategy to guarantee high bioavailability of various drugs. A few years ago, the Solid Crystal Suspension (SCS) technology was suggested, in which crystalline drug particles are ground and dispersed in a highly soluble crystalline carrier by a hot melt extrusion process. The current study demonstrates the scale-up of the SCS technology to standard, lab-scale extrusion equipment - a change from previous investigations, which used small batch sizes. A twin-screw extruder was modified to account for the rapid crystallization of the carrier. The screw speed and the barrel temperature were identified as critical process parameters and were varied systematically in several experimental designs. Finally, parameters were identified that produced extrudates with rapid dissolution rates. After extrusion, the extrudates were milled to granules and then tableted. These tablets were investigated with respect to their bioavailability in beagle dogs. It was found that drug particle size reduction in the hot melt extrusion led to 3.5-fold higher bioavailability in these dogs than occurred with the physical mixture of the used substances. The solid crystal suspension formulation had a slightly higher bioavailability than the marked product. In conclusion, the SCS technology was successfully scaled up to lab-scale equipment, and the concept was confirmed by a bioavailability study. © 2012 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.ejpb.2012.09.012 2013 • 90 Solid dispersions prepared by continuous cogrinding in an air jet mill
Muehlenfeld, C. and Kann, B. and Windbergs, M. and Thommes, M.
Journal of Pharmaceutical Sciences 102 4132-4139 (2013)Embedding a poorly water-soluble drug as a solid dispersion in a hydrophilic carrier by cogrinding is a possible strategy for enhancing the drug dissolution rate. Although general interest in continuous processes for manufacturing drug formulations has increased, many publications still focus on batch processes. The jet mill used in this study is a promising tool for continuous cogrinding. Investigation of different drug-to-carrier ratios (griseofulvin/mannitol) demonstrated that a drug load of 10% is best suited to investigate the enhanced dissolution behavior. To gain deeper insight into the underlying mechanisms, the coground dispersion is compared with different physical mixtures in terms of physicochemical properties and dissolution behavior. Differential scanning calorimetry and X-ray powder diffraction were used to verify the crystalline structure of the coground formulation. On the basis of the Hixson-Crowell model, particle size reduction was ruled out as the main reason for dissolution enhancement. An increase of surface free energies because of grinding is shown with contact angle measurements. Confocal Raman microscopy investigations revealed the drug's bulk dispersity in the coground formulation as an additional factor for the increased dissolution rate. In conclusion, the continuous cogrinding approach is a promising technique to prepare the drug in a rapidly dissolving, yet crystalline, form. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association.
view abstract doi: 10.1002/jps.23731 2013 • 89 Spheronisation mechanism of MCC II-based pellets
Krueger, C. and Thommes, M. and Kleinebudde, P.
Powder Technology 238 176-187 (2013)Microcrystalline cellulose II (MCC II) - a polymorph of commonly used MCC I - was introduced as new pelletisation aid in wet-extrusion/spheronisation. Preliminary investigations suggested that the spheronisation mechanism of MCC II-based pellets differs from the known mechanism of MCC I. Therefore the spheronisation mechanism of MCC II-based pellets was investigated and compared to that of MCC I.The study dealt with the effect of spheroniser load as well as spheronisation speed and time on the pellet properties of shape (aspect ratio), size (equivalent diameter), weight, porosity, size distribution (10%-interval) and yield (fine fraction) of MCC II-based formulations. The parameters were systematically varied in a 33 full factorial design; Furthermore spheronisation time experiments with spheronisation times from 10s to 15min (13 steps) were conducted. For this purpose mixtures with 20% MCC II and 80% lactose or chloramphenicol were chosen. A mixture of 20% MCC I and 80% lactose served as comparison.Regarding the MCC II-based pellets all investigated pellet properties were significantly influenced by spheronisation speed and time, spheroniser load showed nearly no influence. Aspect ratio, 10%-interval and porosity decreased continuously throughout the entire spheronisation process. After a slight decrease, pellet weight and equivalent diameter increased during spheronisation. On the contrary the fine fraction decreased during spheronisation after passing a maximum in the first minutes of spheronisation. MCC I-based pellets behaved differently during spheronisation: Pellet weight remained nearly constant during spheronisation and the equivalent diameter decreased; The fine fraction was lower compared to that of the MCC II-based pellets. The higher fine fraction of MCC II could partly explain this result as the fine fraction layered on the pellets. However, the fine fraction was too low to explain the complete weight gain. Therefore, a new spheronisation mechanism for MCC-II based pellets was proposed: It was suspected that small pellets abraded during processing and layered on the other pellets. This presumption was supported by the high increase of the 10%-interval of the MCC II-based pellets during spheronisation indicating a narrowing of the size distribution; The improvement was less pronounced for the MCC I-based pellets.MCC II behaves in a different manner than MCC I in spheronisation: A deeper insight into the spheronisation of MCC II-based pellets was obtained providing a new pelletisation mechanism that is the basis to control and influence the spheronisation process of MCC II-based pellets. © 2011 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2011.12.052 2013 • 88 Spray roasting of iron chloride FeCl2: Numerical modelling of industrial scale reactors
Schiemann, M. and Wirtz, S. and Scherer, V. and Bärhold, F.
Powder Technology 245 70-79 (2013)Iron chloride solutions are a waste product in steel pickling plants. A technique to recover the spent solutions is a spray roasting process, where the spent solution is sprayed into a hot reaction atmosphere and solid iron oxide particles are formed. The particle history in spray roasting reactors has an important influence on the efficiency of the recovery process and on the quality of the by-product Fe2O3. The iron oxide underlays strong quality demands for further processing. The particle quality is influenced by the plant design and operation parameters. To investigate the influence of those properties on the iron oxide produced in the spray roasting process, a model for CFD simulations has been developed. It describes the particle formation and chemical reaction of the iron chloride solution in the spray roasting reactor in a simplified way suitable for CFD simulations. Simulations of two different industrial reactor configurations show the capability of the model to predict the influence of geometric variations on the composition of the resulting iron oxide. © 2013 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2013.04.034 2013 • 87 Synthesis of one-dimensional hierarchical NiO hollow nanostructures with enhanced supercapacitive performance
Zhang, G. and Yu, L. and Hoster, H.E. and Lou, X.W.
Nanoscale 5 877-881 (2013)One-dimensional hierarchical hollow nanostructures composed of NiO nanosheets are successfully synthesized through a facile carbon nanofiber directed solution method followed by a simple thermal annealing treatment. With the advantages of high electro-active surface area, carbon nanofiber supported robust structure and short ion and electron transport pathways, the hierarchical hybrid nanostructures deliver largely enhanced capacitance with excellent cycling stability when evaluated as electrode materials for supercapacitors. More specifically, a high capacitance of 642 F g-1 is achieved when the charge-discharge current density is 3 A g-1 and the total capacitance loss is only 5.6% after 1000 cycles. © 2013 The Royal Society of Chemistry.
view abstract doi: 10.1039/c2nr33326k 2013 • 86 The transition from spark to arc discharge and its implications with respect to nanoparticle production
Hontañón, E. and Palomares, J.M. and Stein, M. and Guo, X. and Engeln, R. and Nirschl, H. and Kruis, F.E.
Journal of Nanoparticle Research 15 (2013)The synthesis of nanoparticles by means of electrical discharges between two electrodes in an inert gas at atmospheric pressure, as driven by a constant current ranging from a few milliamps to tens of amps, is investigated in this work. An extensive series of experiments are conducted with copper as a consumable electrode and pure nitrogen as the inert gas. Three different DC power supplies are used to drive electrical discharges for the entire operating current range. Then, three electrical discharge regimes (spark, glow, and arc) with distinct voltage-current characteristics and plasma emission spectra are recognized. For the first time, nanoparticles are synthesized by evaporation of an electrode by atmospheric pressure inert gas DC glow discharge of a few millimeters in size. The discharge regimes are characterized in terms of the mass output rate and the particle size distribution of the copper aerosols by means of online (tapered element oscillating microbalance, TEOM; and scanning mobility particle sizer, SPMS) and offline (gravimetric analysis; small and wide angle X-ray scattering, SWAXS; and transmission electron microscopy, TEM) techniques. The electrical power delivered to the electrode gap and the gas flow rate are two major parameters determining the aerosol mass output rate and the aerosol particle size distribution. The mass output rate of copper aerosols raises from 2 mg h-1 to 2 g h-1 when increasing the electrical power from 9 to 900 W. The particle mean size (SMPS dg) varies between 20 and 100 nm depending upon the electrical power and the gas flow rate, whereas the particle size dispersion (SMPS σg) ranges from 1.4 to 1.7 and is only weakly dependent on the gas flow rate. © 2013 Springer Science+Business Media.
view abstract doi: 10.1007/s11051-013-1957-y 2013 • 85 Thermoresponsive ultrafiltration membranes for the switchable permeation and fractionation of nanoparticles
Frost, S. and Ulbricht, M.
Journal of Membrane Science 448 1-11 (2013)Poly(ethylene terephthalate) track-etched ultrafiltration membranes (110. nm pore diameter) have been functionalized with the thermo-responsive polymer poly(N-isopropylacrylamide) (PNIPAAm) via surface-initiated Atom Transfer Radical Polymerization (SI-ATRP). The PNIPAAm chain lengths, i.e. degree of graft functionalization, inside the membrane pores could be controlled very well with polymerization time. Importantly, gas flow/pore dewetting permporometry measurements demonstrated that the pore diameter in the dry state could be reduced and that the narrow pore size distribution of the membranes was not changed during the grafting process. Both hydrodynamic pore diameters of the membranes and grafted hydrodynamic layer thickness on the pore walls as well as their response to temperature could be estimated by measuring water permeability and applying Hagen-Poiseuille law. Defined temperature-induced swelling/deswelling ratios of ~2 had been observed. These data indicate that PNIPAAm chains in the brush state had been achieved. The ultrafiltration membrane pores could be switched between more open and more closed states. For example, the hydrodynamic pore diameter could be switched from 21. nm at 23. °C to 69. nm at 45. °C. For the same type of membrane the rejection of monomodal 21. nm silica nanoparticles could be switched from 99% at 23. °C to only 35% at 45. °C. The rejection for larger monomodal 35. nm silica nanoparticles was above 90% for every functionalized membrane irrespective of the temperature. For an exemplary functionalized membrane evidence for a switchable size-selective NP fractionation has been found. A mixture of the 21 and the 35. nm silica nanoparticles was ultrafiltered through the membrane and at 23. °C only the smaller ones could be found in the permeate whereas at 45. °C also the larger nanoparticles were able to pass the membrane. © 2013.
view abstract doi: 10.1016/j.memsci.2013.07.036 2012 • 84 A numerical study on the influence of particle shape on hopper discharge within the polyhedral and multi-sphere discrete element method
Höhner, D. and Wirtz, S. and Scherer, V.
Powder Technology 226 16-28 (2012)In this study 3D DEM-simulations of hopper discharge using non-cohesive, monodisperse spherical and polyhedral particles as well as particle shapes generated by the multi-sphere method are carried out. For this purpose an overview of the Common Plane algorithm for contact detection between polyhedral particles is given and an important refinement of the contact point definition is presented. In the hopper the effect of increasing particle angularity on the flow properties is investigated. Moreover, three different hopper designs are chosen, to further examine the influence of hopper angle and hopper opening size on the flow properties in combination with varying particle shapes. It is demonstrated that particles with an increasing angularity reduce the mass flow rate from the hopper and in case of the flat bottom hopper (α = 0°) increase the residual quantity after discharge. In all simulations significant differences between polyhedral and clustered particles were observed, which indicates that the type of particle shape approximation is a parameter that has to be considered in DEM-simulations of hopper discharge. © 2012 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2012.03.041 2012 • 83 Adsorption of nanoparticles at the solid-liquid interface
Brenner, T. and Paulus, M. and Schroer, M.A. and Tiemeyer, S. and Sternemann, C. and Möller, J. and Tolan, M. and Degen, P. and Rehage, H.
Journal of Colloid and Interface Science 374 287-290 (2012)The adsorption of differently charged nanoparticles at liquid-solid interfaces was investigated by in situ X-ray reflectivity measurements. The layer formation of positively charged maghemite (γ-Fe 2O 3) nanoparticles at the aqueous solution-SiO 2 interface was observed while negatively charged gold nanoparticles show no adsorption at this interface. Thus, the electrostatic interaction between the particles and the charged surface was determined as the driving force for the adsorption process. The data analysis shows that a logarithmic particle size distribution describes the density profile of the thin adsorbed maghemite layer. The size distribution in the nanoparticle solution determined by small angle X-ray scattering shows an average particle size which is similar to that found for the adsorbed film. The formed magehemite film exhibits a rather high stability. © 2012 Elsevier Inc.
view abstract doi: 10.1016/j.jcis.2012.02.010 2012 • 82 Au, @ZrO 2 yolk-shell catalysts for CO oxidation: Study of particle size effect by ex-post size control of Au cores
Güttel, R. and Paul, M. and Galeano, C. and Schüth, F.
Journal of Catalysis 289 100-104 (2012)Gold nanoparticles supported on transition metal oxides are found to exhibit a pronounced particle size effect in CO oxidation. However, the preparation of comparable supported gold nanoparticles with different sizes remains challenging, since the catalytic behavior of these materials is very sensitive to the preparation conditions. To overcome this difficulty, Au, @ZrO 2 catalysts with gold core sizes between 5 and 15 nm were prepared by partial leaching of gold in an ex-post manner. The material obtained offers a unique comparability for particle size effect studies in CO oxidation. No effect of gold particle size was observed in the studied size range. © 2012 Elsevier Inc. All rights reserved.
view abstract doi: 10.1016/j.jcat.2012.01.021 2012 • 81 Characterizing permeability and stability of microcapsules for controlled drug delivery by dynamic NMR microscopy
Henning, S. and Edelhoff, D. and Ernst, B. and Leick, S. and Rehage, H. and Suter, D.
Journal of Magnetic Resonance 221 11-18 (2012)Microscopic capsules made from polysaccharides are used as carriers for drugs and food additives. Here, we use NMR microscopy to assess the permeability of capsule membranes and their stability under different environmental conditions. The results allow us to determine the suitability of different capsules for controlled drug delivery. As a measure of the membrane permeability, we monitor the diffusion of paramagnetic molecules into the microcapsules by dynamic NMR microimaging. We obtained the diffusion coefficients of the probe molecules in the membranes and in the capsule core by comparing the measured time dependent concentration maps with numerical solutions of the diffusion equation. The results reveal that external coatings strongly decrease the permeability of the capsules. In addition, we also visualized that the capsules are stable under gastric conditions but dissolve under simulated colonic conditions, as required for targeted drug delivery. Depending on the capsule, the timescales for these processes range from 1 to 28 h. © 2012 Elsevier Inc. All rights reserved.
view abstract doi: 10.1016/j.jmr.2012.05.009 2012 • 80 Comparison of micro- and nanoscale Fe +3-containing (Hematite) particles for their toxicological properties in human lung cells in vitro
Bhattacharya, K. and Hoffmann, E. and Schins, R.F.P. and Boertz, J. and Prantl, E.-M. and Alink, G.M. and Byrne, H.J. and Kuhlbusch, T.A.J. and Rahman, Q. and Wiggers, H. and Schulz, C. and Dopp, E.
Toxicological Sciences 126 173-182 (2012)The specific properties of nanoscale particles, large surface-to-mass ratios and highly reactive surfaces, have increased their commercial application in many fields. However, the same properties are also important for the interaction and bioaccumulation of the nonbiodegradable nanoscale particles in a biological system and are a cause for concern. Hematite (α-Fe 2O 3), being a mineral form of Fe(III) oxide, is one of the most used iron oxides besides magnetite. The aim of our study was the characterization and comparison of biophysical reactivity and toxicological effects of α-Fe 2O 3 nano- (d < 100 nm) and microscale (d < 5 μm) particles in human lung cells. Our study demonstrates that the surface reactivity of nanoscale α-Fe 2O 3 differs from that of microscale particles with respect to the state of agglomeration, radical formation potential, and cellular toxicity. The presence of proteins in culture medium and agglomeration were found to affect the catalytic properties of the hematite nano- and microscale particles. Both the nano- and microscale α-Fe 2O 3 particles were actively taken up by human lung cells in vitro, although they were not found in the nuclei and mitochondria. Significant genotoxic effects were only found at very high particle concentrations (> 50 μg/ml). The nanoscale particles were slightly more potent in causing cyto- and genotoxicity as compared with their microscale counterparts. Both types of particles induced intracellular generation of reactive oxygen species. This study underlines that α-Fe 2O 3 nanoscale particles trigger different toxicological reaction pathways than microscale particles. However, the immediate environment of the particles (biomolecules, physiological properties of medium) modulates their toxicity on the basis of agglomeration rather than their actual size. © The Author 2012. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved.
view abstract doi: 10.1093/toxsci/kfs014 2012 • 79 Current induced surface diffusion on a single-crystalline silver nanowire
Kaspers, M.R. and Bernhart, A.M. and Bobisch, C.A. and Möller, R.
Nanotechnology 23 (2012)Scanning tunnelling microscopy was used to study the morphological changes of the surface of a single-crystalline silver nanowire caused by a lateral electron current. At current densities of about 1.5×10 7 A cm -2, surface atoms are extracted from step edges, resulting in the motion of surface steps, islands and holes with a thickness or depth of one monolayer. Upon current reversal the direction of the material transport can be altered. The findings are interpreted in terms of the wind force. © 2012 IOP Publishing Ltd.
view abstract doi: 10.1088/0957-4484/23/20/205706 2012 • 78 Cytotoxicity and ion release of alloy nanoparticles
Hahn, A. and Fuhlrott, J. and Loos, A. and Barcikowski, S.
Journal of Nanoparticle Research 14 (2012)It is well-known that nanoparticles could cause toxic effects in cells. Alloy nanoparticles with yet unknown health risk may be released from cardiovascular implants made of Nickel-Titanium or Cobalt-Chromium due to abrasion or production failure. We show the bio-response of human primary endothelial and smooth muscle cells exposed to different concentrations of metal and alloy nanoparticles. Nanoparticles having primary particle sizes in the range of 5-250 nm were generated using laser ablation in three different solutions avoiding artificial chemical additives, and giving access to formulations containing nanoparticles only stabilized by biological ligands. Endothelial cells are found to be more sensitive to nanoparticle exposure than smooth muscle cells. Cobalt and Nickel nanoparticles caused the highest cytotoxicity. In contrast, Titanium, Nickel- Iron, and Nickel-Titanium nanoparticles had almost no influence on cells below a nanoparticle concentration of 10 lM. Nanoparticles in cysteine dissolved almost completely, whereas less ions are released when nanoparticles were stabilized in water or citrate solution. Nanoparticles stabilized by cysteine caused less inhibitory effects on cells suggesting cysteine to form metal complexes with bioactive ions in media. © Springer Science+Business Media B.V. 2012.
view abstract doi: 10.1007/s11051-011-0686-3 2012 • 77 Determination of the quantum dot band gap dependence on particle size from optical absorbance and transmission electron microscopy measurements
Segets, D. and Lucas, J.M. and Klupp Taylor, R.N. and Scheele, M. and Zheng, H. and Alivisatos, A.P. and Peukert, W.
ACS Nano 6 9021-9032 (2012)This work addresses the determination of arbitrarily shaped particle size distributions (PSDs) from PbS and PbSe quantum dot (QD) optical absorbance spectra in order to arrive at a relationship between band gap energy and particle size over a large size range. Using a modified algorithm which was previously developed for ZnO, we take only bulk absorption data from the literature and match the PSDs derived from QD absorbance spectra with those from transmission electron microscopical (TEM) image analysis in order to arrive at the functional dependence of the band gap on particle size. Additional samples sized solely from their absorbance spectra with our algorithm show excellent agreement with TEM results. We investigate the influence of parameters of the TEM image analysis such as threshold value on the final result. The band gap versus size relationship developed from analysis of just two samples lies well within the bounds of a number of published data sets. We believe that our methodology provides an attractive shortcut for the study of various novel quantum-confined direct band gap semiconductor systems as it permits the band gap energies of a broad size range of QDs to be probed with relatively few synthetic experiments and without quantum mechanical simulations. © 2012 American Chemical Society.
view abstract doi: 10.1021/nn303130d 2012 • 76 Electron transport at surfaces and interfaces
Bobisch, C.A. and Möller, R.
Chimia 66 23-30 (2012)Here we present two techniques which give insight on transport phenomena with atomic resolution. Ballistic electron emission microscopy is used to study the ballistic transport through layered heterogeneous systems. The measured ballistic fraction of the tunneling current provides information about lossless transport channels through metallic layers and organic adsorbates. The transport characteristics of Bi(111)/Si Schottky devices and the influence of the organic adsorbates perylene tetracaboxylic dianhydride acid and C 60 on the ballistic current are discussed. Scanning tunneling potentiometry gives access to the lateral transport along a surface, thus scattering processes within two-dimensional electron systems for the Bi(111) surface and the Si(111)(√3×√3)-Ag surface could be visualized. © Schweizerische Chemische Gesellschaft.
view abstract doi: 10.2533/chimia.2012.23 2012 • 75 Emission measurement and safety assessment for the production process of silicon nanoparticles in a pilot-scale facility
Wang, J. and Asbach, C. and Fissan, H. and Hülser, T. and Kaminski, H. and Kuhlbusch, T.A.J. and Pui, D.Y.H.
Journal of Nanoparticle Research 14 (2012)Emission into the workplace was measured for the production process of silicon nanoparticles in a pilot-scale facility at the Institute of Energy and Environmental Technology e.V. (IUTA). The silicon nanoparticles were produced in a hot-wall reactor and consisted of primary particles around 60 nm in diameter. We employed real-time aerosol instruments to measure particle number and lungdeposited surface area concentrations and size distribution; airborne particles were also collected for offline electron microscopic analysis. Emission of silicon nanoparticles was not detected during the processes of synthesis, collection, and bagging. This was attributed to the completely closed production system and other safety measures against particle release which will be discussed briefly. Emission of silicon nanoparticles significantly above the detection limit was only observed during the cleaning process when the production system was open and manually cleaned. The majority of the detected particles was in the size range of 100-400 nm and were silicon nanoparticle agglomerates first deposited in the tubing then resuspended during the cleaning process. Appropriate personal protection equipment is recommended for safety protection of the workers during cleaning. © 2012 Springer Science+Business Media B.V.
view abstract doi: 10.1007/s11051-012-0759-y 2012 • 74 Impact of spacer and strand length on oligonucleotide conjugation to the surface of ligand-free laser-generated gold nanoparticles
Barchanski, A. and Hashimoto, N. and Petersen, S. and Sajti, C.L. and Barcikowski, S.
Bioconjugate Chemistry 23 908-915 (2012)Gold nanoparticles conjugated to nucleic acids are widely used for biomedical targeting and sensing applications; however, little is known about the conjugation chemistry covering the impact of steric dimension and strand orientation of single-stranded oligonucleotides (ssO) on the conjugation process and binding efficiencies. In this context, we present an extensive investigation concerning the attachment of thiolated ssO to the surface of laser-generated gold nanoparticles, altering both strand length and binding orientation by the insertion of different spacer types at either the 3′ or 5′ ssO terminus. A significant reduction of conjugation efficiency of about 30-50% is determined for spacer-prolonged bionanoconjugates due to coiling effects of the flexible ssO strand on the particle surface which increases deflection angle of oligonucleotides and limits the number of biomolecules attached to the nanoparticles. © 2012 American Chemical Society.
view abstract doi: 10.1021/bc200462b 2012 • 73 Influence of particle diameter and material properties on mixing of monodisperse spheres on a grate: Experiments and discrete element simulation
Simsek, E. and Sudbrock, F. and Wirtz, S. and Scherer, V.
Powder Technology 221 144-154 (2012)The Discrete Element Method (DEM) can help to obtain detailed information on the mixing process within a bed of fuel particles on grate firing systems. In a first study it was shown by comparing experiments on a generic grate with DEM simulations that for a granulate consisting of monodisperse spheres the influence of grate stroke length and bar velocity can be reproduced. Prior to tackling particle assemblies which are polydisperse and consist of particles of complex shape it has to be shown that the influence of particle diameter and material properties of the particles is described correctly by DEM simulations. Thus experiments with monodisperse spheres of three different diameters (5, 10, 20. mm) and two materials (plastic, wood) are compared to DEM simulations. The mixing process is measured at the front side wall and at the top surface of the particle bed and quantified by image analysis. Both visual observation and mixing parameter results attest a very good agreement between experiments and simulations. The influence of particle diameter and material properties measured in the experiments can be reproduced by DEM simulations. © 2011 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2011.12.051 2012 • 72 Interplay of wrinkles, strain, and lattice parameter in graphene on iridium
Hattab, H. and N'Diaye, A.T. and Wall, D. and Klein, C. and Jnawali, G. and Coraux, J. and Busse, C. and Van Gastel, R. and Poelsema, B. and Michely, T. and Meyer zu Heringdorf, F.-J. and Horn-von Hoegen, M.
Nano Letters 12 678-682 (2012)Following graphene growth by thermal decomposition of ethylene on Ir(111) at high temperatures we analyzed the strain state and the wrinkle formation kinetics as function of temperature. Using the moiré spot separation in a low energy electron diffraction pattern as a magnifying mechanism for the difference in the lattice parameters between Ir and graphene, we achieved an unrivaled relative precision of ±0.1 pm for the graphene lattice parameter. Our data reveals a characteristic hysteresis of the graphene lattice parameter that is explained by the interplay of reversible wrinkle formation and film strain. We show that graphene on Ir(111) always exhibits residual compressive strain at room temperature. Our results provide important guidelines for strategies to avoid wrinkling. © 2011 American Chemical Society.
view abstract doi: 10.1021/nl203530t 2012 • 71 Magnetic switchable alginate beads
Degen, P. and Leick, S. and Siedenbiedel, F. and Rehage, H.
Colloid and Polymer Science 290 97-106 (2012)Calcium alginate beads are enclosed in a wide range of products including food, pharmaceuticals, and cosmetic formulations. The biopolymer matrix is often used to stabilize active ingredients and to provide a controlled release under well-defined conditions. In this context, it is of high interest to study the magnetic-induced attraction, elongation, and rupture of capsules or beads. In this work, we synthesized new types of magnetic switchable alginate beads. The magnetic sensitivity was achieved by incorporation of magnetic nanoparticles (MNPs) within the alginate gel. We measured the mechanical properties of single alginate beads in squeezing experiments, the evaporation of water and the magnetic sensitivity by stimulation of these beads in external fields. In all these measurements, the alginate and the nanoparticle concentration were systematically varied. We could show that the incorporation of MNPs generates a magnetic response of the beads and reduces the evaporation of water but has no influence on the mechanical stability of the beads during compression. Calculations of the shear modulus by means of the squeezing data result in good agreement in comparison to the shear moduli measured by rheological frequency sweep tests. With scanning electron microscopy, we could analyze the molecular structure of such composite systems, and we observed a homogeneous distribution of the MNPs within the gel matrix. © Springer-Verlag 2011.
view abstract doi: 10.1007/s00396-011-2524-7 2012 • 70 Mathematical description of experimentally determined charge distributions of a unipolar diffusion charger
Kaminski, H. and Kuhlbusch, T.A.J. and Fissan, H. and Ravi, L. and Horn, H.-G. and Han, H.-S. and Caldow, R. and Asbach, C.
Aerosol Science and Technology 46 708-716 (2012)The charge distributions of an improved opposed flow unipolar diffusion charger were measured using a tandem differential mobility analyzer (DMA) set up in a size range of approximately 20-400 nm. The charger is intended to be used in a portable aerosol sizer to measure particle size distributions. The determined charge distributions were represented by lognormal distributions, and a set of equations and coefficients was developed to calculate the charge distributions. These equations can be easily implemented in software for size distribution measurements. The agreement between the mathematically derived and measured charge distributions is very good, with regression coefficients R 2 >0.96. The investigations showed that approximately 55% of 20-nm particles remain uncharged, while up to 25 elementary charges need to be considered for multiple charge correction of 400-nm particles. Comparison with the Fuchs theory delivered satisfying agreement with the measured average charge levels, but charge distributions cannot be described by the Fuchs theory, likely caused by the charger geometry. Copyright © American Association for Aerosol Research.
view abstract doi: 10.1080/02786826.2012.659360 2012 • 69 Microgradient-heaters as tools for high-throughput experimentation
Meyer, R. and Hamann, S. and Ehmann, M. and Thienhaus, S. and Jaeger, S. and Thiede, T. and Devi, A. and Fischer, R.A. and Ludwig, Al.
ACS Combinatorial Science 14 531-536 (2012)A microgradient-heater (MGH) was developed, and its feasibility as a tool for high-throughput materials science experimentation was tested. The MGH is derived from microhot plate (MHP) systems and allows combinatorial thermal processing on the micronano scale. The temperature gradient is adjustable by the substrate material. For an Au-coated MGH membrane a temperature drop from 605 to 100 °C was measured over a distance of 965 μm, resulting in an average temperature change of 0.52 K/μm. As a proof of principle, we demonstrate the feasibility of MGHs on the example of a chemical vapor deposition (CVD) process. The achieved results show discontinuous changes in surface morphology within a continuous TiO 2 film. Furthermore the MGH can be used to get insights into the energetic relations of film growth processes, giving it the potential for microcalorimetry measurements. © 2012 American Chemical Society.
view abstract doi: 10.1021/co3000488 2012 • 68 Microwave-hydrothermal synthesis and characterization of nanostructured copper substituted ZnM 2O 4(M = Al, Ga) spinels as precursors for thermally stable Cu catalysts
Conrad, F. and Massue, C. and Kühl, S. and Kunkes, E. and Girgsdies, F. and Kasatkin, I. and Zhang, B. and Friedrich, M. and Luo, Y. and Armbrüster, M. and Patzke, G.R. and Behrens, M.
Nanoscale 4 2018-2028 (2012)Nanostructured Cu<inf>x</inf>Zn<inf>1-x</inf>Al<inf>2</inf>O<inf>4</inf> with a Cu:Zn ratio of: has been prepared by a microwave-assisted hydrothermal synthesis at 150°C and used as a precursor for Cu/ZnO/Al<inf>2</inf>O <inf>3</inf>-based catalysts. The spinel nanoparticles exhibit an average size of approximately 5 nm and a high specific surface area (above 250 m2 g-1). Cu nanoparticles of an average size of 3.3 nm can be formed by reduction of the spinel precursor in hydrogen and the accessible metallic Cu(0) surface area of the reduced catalyst was 8 m2 g-1. The catalytic performance of the material in CO<inf>2</inf> hydrogenation and methanol steam reforming was compared with conventionally prepared Cu/ZnO/Al<inf>2</inf>O<inf>3</inf> reference catalysts. The observed lower performance of the spinel-based samples is attributed to a lack of synergetic interaction of the Cu nanoparticles with ZnO due to the incorporation of Zn 2+ in the stable spinel lattice. Despite its lower performance, however, the nanostructured nature of the spinel catalyst was stable after thermal treatment up to 500°C in contrast to other Cu-based catalysts. Furthermore, a large fraction of the re-oxidized copper migrates back into the spinel upon calcination of the reduced catalyst, thereby enabling a regeneration of sintered catalysts after prolonged usage at high temperatures. Similarly prepared samples with Ga instead of Al exhibit a more crystalline catalyst with a spinel particle size around 20 nm. The slightly decreased Cu(0) surface area of 3.2 m2 g-1 due to less copper incorporation is not a significant drawback for the methanol steam reforming. © The Royal Society of Chemistry 2012.
view abstract doi: 10.1039/c2nr11804a 2012 • 67 Monodispersity and size control in the synthesis of 20-100 nm quasi-spherical silver nanoparticles by citrate and ascorbic acid reduction in glycerol-water mixtures
Steinigeweg, D. and Schlücker, S.
Chemical Communications 48 8682-8684 (2012)A simple two-step seed-mediated synthesis of monodisperse quasi-spherical silver nanoparticles by citrate and ascorbic acid reduction is presented. Control over monodispersity is achieved by a variety of compounds with hydroxyl groups such as glycerol, ethylene glycol, agarose, or sucrose. The latter can also be used as a matrix for storage. © 2012 The Royal Society of Chemistry.
view abstract doi: 10.1039/c2cc33850e 2012 • 66 Non-syngas direct steam reforming of methanol to hydrogen and carbon dioxide at low temperature
Yu, K.M.K. and Tong, W. and West, A. and Cheung, K. and Li, T. and Smith, G. and Guo, Y. and Tsang, S.C.E.
Nature Communications 3 (2012)A non-syngas direct steam reforming route is investigated for the conversion of methanol to hydrogen and carbon dioxide over a CuZnGaOx catalyst at 150-200 °C. This route is in marked contrast with the conventional complex route involving steam reformation to syngas (CO/H 2) at high temperature, followed by water gas shift and CO cleanup stages for hydrogen production. Here we report that high quality hydrogen and carbon dioxide can be produced in a single-step reaction over the catalyst, with no detectable CO (below detection limit of 1 ppm). This can be used to supply proton exchange membrane fuel cells for mobile applications without invoking any CO shift and cleanup stages. The working catalyst contains, on average, 3-4 nm copper particles, alongside extremely small size of copper clusters stabilized on a defective ZnGa2O4 spinel oxide surface, providing hydrogen productivity of 393.6 ml g-1-cat h-1 at 150 °C. © 2012 Macmillan Publishers Limited. All rights reserved.
view abstract doi: 10.1038/ncomms2242 2012 • 65 On the effect of molecular and hydrocarbon-bonded hydrogen on carbon particle formation in C 3O 2 pyrolysis behind shock waves
Böhm, H. and Emelianov, A. and Eremin, A. and Schulz, C. and Jander, H.
Combustion and Flame 159 932-939 (2012)The effect of H 2 and C 2H 2 addition on particle formation in the pyrolysis of C 3O 2/Ar mixtures was studied behind reflected shock waves. An existing reaction mechanism for the pyrolysis of highly-diluted C 3O 2 in argon was expanded to conditions with higher C 3O 2 concentrations (up to 33volume%) at elevated pressures and high temperatures and was validated against experimental data. The simulations for the gas-phase chemistry were performed with the program CHEMKIN. The heterogeneous particle formation was modeled by post-processing using the program PREDICI relying on the Galerkin method. It was found that in C 3O 2/H 2/Ar pyrolysis, the induction times and rate constants of particle formation do not differ significantly from those of pure C 3O 2/Ar pyrolysis. However, the presence of H 2 reduced the particle volume fraction, the mean diameter of particles, the particle number density, and the maximum temperature rise of the mixture. Hydrocarbon-bonded hydrogen in C 3O 2/C 2H 2/Ar pyrolysis caused significantly increased induction times for particle formation, decreased particle volume fractions, and decreased temperature rises. The different reaction channels for carbon particle formation were identified in view of the role of hydrogen. An alternating reaction channel including C 2 species played an important role in forming polycyclic aromatic hydrocarbons (PAH) in the mixtures. © 2011 The Combustion Institute.
view abstract doi: 10.1016/j.combustflame.2011.09.012 2012 • 64 Quantification of mass transfer during spheronisation
Koester, M. and Thommes, M.
AAPS PharmSciTech 13 493-497 (2012)Spherical granules (pellets) are quite useful in many pharmaceutical applications. The extrusion spheronisation technique is well established as a method of producing pellets of a spherical shape and narrow size distribution. After the extrusion, the cylindrical extrudates are transformed to spherical pellets by spheronisation. The frequently used models consider deformation and breakage during this process. However, the adhesion of fine particles has been neglected as a mechanism in spheronisation for many years. This study quantifies the mass transfer between pellets during spheronisation. During the investigation, the pelletisation aids (microcrystalline cellulose and kappa-carrageenan), the drug (acetaminophen and ibuprofen) and water content were varied systematically. A novel parameter, namely, the "mass transfer fraction " (MTF), was defined to quantify the mass transfer between the pellets. All four investigated formulations had an MTF between 0.10 and 0.52 that implies that up to 50 % of the final pellet weight was involved in mass transfer. Both pelletisation aids showed similar MTF, independent of the drug used. Furthermore, an increase of the MTF, with respect to an increase of the water content, was found for microcrystalline cellulose formulations. In conclusion, the mass transfer between the pellets has to be considered as a mechanism for spheronisation. © 2012 American Association of Pharmaceutical Scientists.
view abstract doi: 10.1208/s12249-012-9770-y 2012 • 63 Self-assembled iron oxide nanoparticle multilayer: X-ray and polarized neutron reflectivity
Mishra, D. and Benitez, M.J. and Petracic, O. and Badini Confalonieri, G.A. and Szary, P. and Brüssing, F. and Theis-Bröhl, K. and Devishvili, A. and Vorobiev, A. and Konovalov, O. and Paulus, M. and Sternemann, C. and Toperverg...
Nanotechnology 23 (2012)We have investigated the structure and magnetism of self-assembled, 20nm diameter iron oxide nanoparticles covered by an oleic acid shell for scrutinizing their structural and magnetic correlations. The nanoparticles were spin-coated on an Si substrate as a single monolayer and as a stack of 5ML forming a multilayer. X-ray scattering (reflectivity and grazing incidence small-angle scattering) confirms high in-plane hexagonal correlation and a good layering property of the nanoparticles. Using polarized neutron reflectivity we have also determined the long range magnetic correlations parallel and perpendicular to the layers in addition to the structural ones. In a field of 5kOe we determine a magnetization value of about 80% of the saturation value. At remanence the global magnetization is close to zero. However, polarized neutron reflectivity reveals the existence of regions in which magnetic moments of nanoparticles are well aligned, while losing order over longer distances. These findings confirm that in the nanoparticle assembly the magnetic dipoledipole interaction is rather strong, dominating the collective magnetic properties at room temperature. © 2012 IOP Publishing Ltd.
view abstract doi: 10.1088/0957-4484/23/5/055707 2012 • 62 Silver, gold, and alloyed silver-gold nanoparticles: Characterization and comparative cell-biologic action
Mahl, D. and Diendorf, J. and Ristig, S. and Greulich, C. and Li, Z.A. and Farle, M. and Köller, M. and Epple, M.
Journal of Nanoparticle Research 14 (2012)Silver, gold, and silver-gold-alloy nanoparticles were prepared by citrate reduction modified by the addition of tannin during the synthesis, leading to a reduction in particle size by a factor of three. Nanoparticles can be prepared by this easy waterbased synthesis and subsequently functionalized by the addition of either tris(3-sulfonatophenyl)phosphine or poly(N-vinylpyrrolidone). The resulting nanoparticles of silver (diameter 15-25 nm), gold (5-6 nm), and silver-gold (50:50; 10-12 nm) were easily dispersable in water and also in cell culture media (RPMI + 10 % fetal calf serum), as shown by nanoparticle tracking analysis and differential centrifugal sedimentation. High-resolution transmission electron microscopy showed a polycrystalline nature of all nanoparticles. EDX on single silver-gold nanoparticles indicated that the concentration of gold is higher inside a nanoparticle. The biologic action of the nanoparticles toward human mesenchymal stem cells (hMSC) was different: Silver nanoparticles showed a significant concentration-dependent influence on the viability of hMSC. Gold nanoparticles showed only a small effect on the viability of hMSC after 7 days. Surprisingly, silver-gold nanoparticles had no significant influence on the viability of hMSC despite the silver content. Silver nanoparticles and silver-gold nanoparticles in the concentration range of 5-20 μg mL -1 induced the activation of hMSC as indicated by the release of IL-8. In contrast, gold nanoparticles led to a reduction of the release of IL-6 and IL-8. © Springer Science+Business Media B.V. 2012.
view abstract doi: 10.1007/s11051-012-1153-5 2012 • 61 Spatial variation of PM2.5, PM10, PM2.5 absorbance and PMcoarse concentrations between and within 20 European study areas and the relationship with NO2 - Results of the ESCAPE project
Eeftens, M. and Tsai, M.-Y. and Ampe, C. and Anwander, B. and Beelen, R. and Bellander, T. and Cesaroni, G. and Cirach, M. and Cyrys, J. and de Hoogh, K. and De Nazelle, A. and de Vocht, F. and Declercq, C. and Dedele, A. and Erik...
Atmospheric Environment 62 303-317 (2012)The ESCAPE study (European Study of Cohorts for Air Pollution Effects) investigates relationships between long-term exposure to outdoor air pollution and health using cohort studies across Europe. This paper analyses the spatial variation of PM2.5, PM2.5 absorbance, PM10 and PMcoarse concentrations between and within 20 study areas across Europe.We measured NO2, NOx, PM2.5, PM2.5 absorbance and PM10 between October 2008 and April 2011 using standardized methods. PMcoarse was determined as the difference between PM10 and PM2.5. In each of the twenty study areas, we selected twenty PM monitoring sites to represent the variability in important air quality predictors, including population density, traffic intensity and altitude. Each site was monitored over three 14-day periods spread over a year, using Harvard impactors. Results for each site were averaged after correcting for temporal variation using data obtained from a reference site, which was operated year-round.Substantial concentration differences were observed between and within study areas. Concentrations for all components were higher in Southern Europe than in Western and Northern Europe, but the pattern differed per component with the highest average PM2.5 concentrations found in Turin and the highest PMcoarse in Heraklion. Street/urban background concentration ratios for PMcoarse (mean ratio 1.42) were as large as for PM2.5 absorbance (mean ratio 1.38) and higher than those for PM2.5 (1.14) and PM10 (1.23), documenting the importance of non-tailpipe emissions. Correlations between components varied between areas, but were generally high between NO2 and PM2.5 absorbance (average R2 = 0.80). Correlations between PM2.5 and PMcoarse were lower (average R2 = 0.39). Despite high correlations, concentration ratios between components varied, e.g. the NO2/PM2.5 ratio varied between 0.67 and 3.06.In conclusion, substantial variability was found in spatial patterns of PM2.5, PM2.5 absorbance, PM10 and PMcoarse. The highly standardized measurement of particle concentrations across Europe will contribute to a consistent assessment of health effects across Europe. © 2012 Elsevier Ltd.
view abstract doi: 10.1016/j.atmosenv.2012.08.038 2012 • 60 Spray roasting of iron chloride FeCl 2: Laboratory scale experiments and a model for numerical simulation
Schiemann, M. and Wirtz, S. and Scherer, V. and Bärhold, F.
Powder Technology 228 301-308 (2012)Iron chloride solutions are a waste product in steel pickling plants. A technique to recover the spent solutions is the so-called spray roasting process, where the spent solution is sprayed into a hot reaction atmosphere and solid iron oxide particles are formed. The particle formation in spray roasting reactors has important influence on the efficiency of the recovery process and on the quality of the desired by-product Fe 2O 3. A laboratory reactor was designed to investigate the particle formation. Experiments were carried out covering the predominant conditions in spray roasting reactors. The results offer valuable insight into the particle formation process, providing data on the surface structure of the Fe 2O 3 particles formed and on the progress of chemical conversion. Based on these results, a simplified model applicable to CFD-modelling of spray roasting reactors has been developed. Simulations of particle trajectories in the laboratory reactor are presented to show the capabilities of the model. © 2012 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2012.05.037 2012 • 59 The influence of particle size and spacing on the fragmentation of nanocomposite anodes for Li batteries
Dimitrijevic, B.J. and Aifantis, K.E. and Hackl, K.
Journal of Power Sources 206 343-348 (2012)Experimental evidence has shown that composites comprised Si and Sn nanoparticles embedded inside a matrix are the most promising next generation anodes for Li-ion batteries. This is due to the ability of the matrix material to constrain/buffer the up to 300 volume expansion that Sn and Si undergo upon the formation of lithium rich alloys. Damage still occurs at the nanoparticle/matrix interface, and hence further materials design is required in order to commercialize such anodes. Initial theoretical works have predicted that low volume fractions and high aspect ratios of the nanoparticles result in a greater mechanical stability and hence better capacity retention. The most important design parameters, however, such as particle size and spacing have not been considered theoretically. In the present study, therefore, a gradient enhanced damage model will be employed to predict that damage during Li-insertion, is negligible when the particle size is 20 nm, and the interparticle half-spacing greater then 1.5 times the particle diameter. Furthermore, from the matrix materials considered herein graphene is predicted to be the most promising matrix, which is consistent with recent experimental data. © 2012 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.jpowsour.2012.01.065 2012 • 58 The Role of Oxygen- and Nitrogen-containing Surface Groups on the Sintering of Iron Nanoparticles on Carbon Nanotubes in Different Atmospheres
Sánchez, M.D. and Chen, P. and Reinecke, T. and Muhler, M. and Xia, W.
ChemCatChem 4 1997-2004 (2012)The sintering of iron nanoparticles on carbon nanotubes (CNTs) under different atmospheres was investigated. CNTs were first treated with HNO3 vapor at 200°C to obtain O-functionalized CNTs (OCNTs). The OCNTs were treated in ammonia at 400°C to obtain N-doped CNTs (NCNTs). Highly dispersed FeOx nanoparticles were subsequently deposited by chemical vapor deposition from ferrocene under oxidizing conditions. The obtained FeOx/OCNT and FeOx/NCNT samples were allowed to sinter at 500°C under flowing helium, hydrogen, or ammonia. The samples were studied by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. A significant increase in particle size and a decrease in Fe surface atomic concentration were observed in all the sintered samples. The sintering on OCNTs was more severe than on NCNTs, which can be attributed to stronger metal-substrate interactions and a higher amount of surface defects on NCNTs. The applied gas atmosphere had a substantial influence on the sintering behavior of the nanoparticles: treatment in helium led to the growth of particles and a significant widening of particle size distributions, whereas treatment in hydrogen or ammonia resulted in the growth of particles, but not in the widening of particle size distributions. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/cctc.201200286 2012 • 57 Thin-film transistors with a channel composed of semiconducting metal oxide nanoparticles deposited from the gas phase
Busch, C. and Schierning, G. and Theissmann, R. and Nedic, A. and Kruis, F.E. and Schmechel, R.
Journal of Nanoparticle Research 14 (2012)The fabrication of semiconducting functional layers using low-temperature processes is of high interest for flexible printable electronics applications. Here, the one-step deposition of semiconducting nanoparticles from the gas phase for an active layer within a thin-film transistor is described. Layers of semiconducting nanoparticles with a particle size between 10 and 25 nm were prepared by the use of a simple aerosol deposition system, excluding potentially unwanted technological procedures like substrate heating or the use of solvents. The nanoparticles were deposited directly onto standard thin-film transistor test devices, using thermally grown silicon oxide as gate dielectric. Proof-of-principle experiments were done deploying two different wide-band gap semiconducting oxides, tin oxide, SnO x, and indium oxide, In 2O 3. The tin oxide spots prepared from the gas phase were too conducting to be used as channel material in thin-film transistors, most probably due to a high concentration of oxygen defects. Using indium oxide nanoparticles, thin-film transistor devices with significant field effect were obtained. Even though the electron mobility of the investigated devices was only in the range of 10 -6 cm 2V -1s -1, the operability of this method for the fabrication of transistors was demonstrated. With respect to the possibilities to control the particle size and layer morphology in situ during deposition, improvements are expected. © 2012 Springer Science+Business Media B.V.
view abstract doi: 10.1007/s11051-012-0888-3 2012 • 56 Total surface area concentration measurements of nanoparticles in gases with an electrical sensor
Fissan, H. and Asbach, C. and Kaminski, H. and Kuhlbusch, T.A.J.
Chemie-Ingenieur-Technik 84 365-372 (2012)Nano-objects with different chemical compositions and structures (shapes) are very important building blocks for nanostructured materials. The characterization of the nanoparticles in the gas phase during synthesis and their use is of great importance. The total nanoparticle surface area concentration is essential especially for describing interface processes, because of the increasing surface area per unit of mass with decreasing particle size. In this paper the possible use of an electrical sensor for measuring total surface area concentrations of spherical and agglomerated/aggregated nanoparticles in aerosols is discussed. The electrical sensor, a combination of a unipolar charger and an electrometer, is an easy to use instrument for measuring different measures of nanoparticle concentrations, especially the total surface area concentration deposited in different regions of the lung. The possible use for investigation of nanoparticles in aerosols is discussed. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/cite.201100213 2012 • 55 Toward highly stable electrocatalysts via nanoparticle pore confinement
Galeano, C. and Meier, J.C. and Peinecke, V. and Bongard, H. and Katsounaros, I. and Topalov, A.A. and Lu, A. and Mayrhofer, K.J.J. and Schüth, F.
Journal of the American Chemical Society 134 20457-20465 (2012)The durability of electrode materials is a limiting parameter for many electrochemical energy conversion systems. In particular, electrocatalysts for the essential oxygen reduction reaction (ORR) present some of the most challenging instability issues shortening their practical lifetime. Here, we report a mesostructured graphitic carbon support, Hollow Graphitic Spheres (HGS) with a specific surface area exceeding 1000 m2 g-1 and precisely controlled pore structure, that was specifically developed to overcome the long-term catalyst degradation, while still sustaining high activity. The synthetic pathway leads to platinum nanoparticles of approximately 3 to 4 nm size encapsulated in the HGS pore structure that are stable at 850 C and, more importantly, during simulated accelerated electrochemical aging. Moreover, the high stability of the cathode electrocatalyst is also retained in a fully assembled polymer electrolyte membrane fuel cell (PEMFC). Identical location scanning and scanning transmission electron microscopy (IL-SEM and IL-STEM) conclusively proved that during electrochemical cycling the encapsulation significantly suppresses detachment and agglomeration of Pt nanoparticles, two of the major degradation mechanisms in fuel cell catalysts of this particle size. Thus, beyond providing an improved electrocatalyst, this study describes the blueprint for targeted improvement of fuel cell catalysts by design of the carbon support. © 2012 American Chemical Society.
view abstract doi: 10.1021/ja308570c 2012 • 54 Toward remote-controlled valve functions via magnetically responsive capillary pore membranes
Himstedt, H.H. and Yang, Q. and Qian, X. and Ranil Wickramasinghe, S. and Ulbricht, M.
Journal of Membrane Science 423-424 257-266 (2012)Polyethyleneterephthalate track-etched membranes with a pore diameter of 650nm were functionalized via surface-initiated atom transfer radical polymerization with grafted poly(2-hydroxyethylmethacrylate). Grafted chain length and density were varied. Superparamagnetic nanoparticles (Fe 3O 4; core diameter 15nm) were selectively covalently coupled to the end groups of the grafted chains. The membranes were characterized by grafting degree, X-ray photoelectron spectroscopy, electron microscopy, zeta potential and pore size in dry state via gas flow/pore dewetting permporometry. The results confirmed that all functionalization steps were well controlled. Water permeability measurements allowed estimation of the hydrodynamic pore diameter of the membranes, and, hence, the hydrodynamic polymer layer thickness on the pore walls. The water permeability of the nanoparticle hybrid membranes was then measured in a static or an alternating external magnetic field. Significant and reversible decreases of permeability were observed, with the largest effects for membranes with high polymer grafting density and long polymer chains (hydrodynamic layer thickness up to 100nm). The maximum change in effective pore diameter was only 6%. However, the estimated change of swollen polymer layer thickness (originally between 60 and 100nm) was up to 13nm. The functionality of the membranes can be tuned by variations of straightforward parameters such as pore size or grafted chain lengths. The study is also relevant as a model system for altering the effective thickness of grafted polymer layers on a surface by an external magnetic field for other applications, for instance in microfluidic systems. © 2012 Elsevier B.V.
view abstract doi: 10.1016/j.memsci.2012.08.015 2012 • 53 Toxicity of gold nanoparticles on somatic and reproductive cells
Taylor, U. and Barchanski, A. and Garrels, W. and Klein, S. and Kues, W. and Barcikowski, S. and Rath, D.
Advances in Experimental Medicine and Biology 733 125-133 (2012)Along with the number of potential applications for gold nanoparticles (AuNP) especially for medical and scientific purposes, the interest in possible toxic effects of such particles is rising. The general perception views nanosized gold colloids as relatively inert towards biological systems. However, a closer analysis of pertinent studies reveals a more complex picture. While the chemical compound of which the nanoparticles consists plays an important role, further biocompatibility determining aspects have been made out. The vast majority of trials concerning AuNP-toxicity were performed using somatic cell culture lines. The results show a considerable dependency of toxic effects on size, zeta potential and surface functionalisation. In vivo studies on this subject are still rare. Based on the existing data it can be assumed, that a dosage of under <400 μg Au/kg showed no untoward effects. If higher amounts were applied toxicity depended on route of administration and particle size. Since nanoparticles have been shown to cross reproduction-relevant biological barriers such as the blood-testicle and the placental barrier the question of their reprotoxicity arises. Yet data concerning this subject is far from adequate. Regarding gametes, recent experiments showed a dose-dependent sensitivity of spermatozoa towards AuNP. Oocytes have not yet been tested in that respect. Interestingly, so far no effects were detected on embryos after gold nanoparticle exposure. In conclusion, the biocompatibility of gold nanoparticles depends on a range of particle specific aspects as well as the choice of target tissue. Further clarification of such matters are subject to ongoing research. © 2012 Springer Science+Business Media B.V.
view abstract doi: 10.1007/978-94-007-2555-3_12 2011 • 52 3D self-assembled plasmonic superstructures of gold nanospheres: Synthesis and characterization at the single-particle level
Gellner, M. and Steinigeweg, D. and Ichilmann, S. and Salehi, M. and Schütz, M. and Kömpe, K. and Haase, M. and Schlücker, S.
Small 7 3445-3451 (2011)The synthesis of 3D self-assembled plasmonic superstructures of gold nanospheres as well as the characterization of their structural and optical properties at the single-particle level is presented. This experimental work is complemented by FEM (finite element method) simulations of elastic scattering spectra and the spatial |E| 4 distribution for establishing structure-activity correlations in these complex 3D nanoclusters. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/smll.201102009 2011 • 51 800mg Darunavir tablets prepared by hot melt extrusion
Thommes, M. and Baert, L. and Rosier, J.
Pharmaceutical Development and Technology 16 645-650 (2011)Darunavir (TMC 114) is a protease inhibitor used in the therapy of HIV-1. The aim of this study was to formulate 800mg of Darunavir in a single unit dosage form, with suitable mechanical properties and dissolution behavior, using a corotating twin screw extruder. In preliminary investigations, extrudates of 1mm diameter were prepared to evaluate the extrusion and dissolution behavior of Darunavir. Two different poloxamers (188 and 407) were used to modify the dissolution properties of Darunavir, and a higher solubilization for poloxamer 188 was observed. Furthermore, a zero order drug release from pure Darunavir extrudates was found which was modulated by the extrudate diameter. Extrudates of 13mm diameter were cut into tablets containing 800mg of Darunavir. Due to the lower specific surface area in comparison to the 1mm extrudates, an addition of solubilizing agent was required to obtain the desired dissolution profiles. Therefore, the influence of Mannitol and poloxamer 188 was investigated in different formulations. The formulations exhibited acceptable extrusion behavior and dissolution properties. © 2011 Informa Healthcare USA, Inc.
view abstract doi: 10.3109/10837450.2010.508077 2011 • 50 A facile synthesis of mesoporous crystalline tin oxide films involving a base-triggered formation of sol-gel building blocks
Fried, D.I. and Ivanova, A. and Müller, V. and Rathousky, J. and Smarsly, B.M. and Fattakhova-Rohlfing, D.
Nanoscale 3 1234-1239 (2011)We have developed a new facile procedure for manufacturing crystalline thin films of SnO2 with a uniform mesoporous architecture and full crystallinity of the walls. The procedure is based on the evaporation-induced self-assembly (EISA) of prehydrolyzed tin oxide precursor directed by a commercially available Pluronic polymer. The formation of the tin oxide precursor, which can be self-assembled into a mesoporous structure, is achieved by an addition of ammonium hydroxide to a tin tetrachloride solution. The relative concentration of ammonium hydroxide as well as the duration and temperature of the hydrolysis reaction influence significantly the properties of hydrolyzed tin oxide species and the mesostructure assembled from them. The films coated from these precursor solutions and calcined at 300 °C to 400 °C exhibit a well-developed worm-like porosity with a wall to wall distance of ca. 18 nm, a surface area of up to 50 cm2 cm-2 (corresponding to 55 ± 5 m2 g-1), and high crystallinity. © 2011 The Royal Society of Chemistry.
view abstract doi: 10.1039/c0nr00872a 2011 • 49 A low pressure drop preseparator for elimination of particles larger than 450 nm
Asbach, C. and Fissan, H. and Kaminski, H. and Kuhlbusch, T.A.J. and Pui, D.Y.H. and Shin, H. and Horn, H.G. and Hase, T.
Aerosol and Air Quality Research 11 487-496 (2011)Measurement techniques which allow the detection of airborne nanoparticles are of great interest for e.g. exposure monitoring and quality control during nanoparticle production. An increasing number of commercial devices use a unipolar diffusion charger to charge the particles and determine the nanoparticle concentration and sometimes size. The analysis however may be biased by the presence of large particles. We therefore developed a preseparator that removes particles larger than 450 nm, i.e the minimum in the range of particle lung deposition curves, but only causes a low pressure drop. The preseparator uses a total flow rate of 2.5 L/min and consists of two stages. The first stage is a virtual impactor that removes particles larger than approximately 1 μm with a minor flow of 1 L/min. Particles above 450 nm are removed from the remaining 1.5 L/min in the cyclone of the second stage. The combination of a cyclone with a virtual impactor was shown to reduce the pressure drop of the preseparator from 8.1 to 5.6 kPa compared with a cyclone alone and improve the sharpness of the separation curve for cut-off diameters around 450 nm. Furthermore the virtual impactor extends the cleaning intervals of the preseparator, because large particles are no longer deposited in the cyclone. Eventually the preseparator was tested with an opposed flow diffusion charger and it was shown that particle charging is not affected by the pressure drop. © Taiwan Association for Aerosol Research.
view abstract doi: 10.4209/aaqr.2011.05.0057 2011 • 48 Cell type-specific responses of peripheral blood mononuclear cells to silver nanoparticles
Greulich, C. and Diendorf, J. and Geßmann, J. and Simon, T. and Habijan, T. and Eggeler, G. and Schildhauer, T.A. and Epple, M. and Köller, M.
Acta Biomaterialia 7 3505-3514 (2011)Silver nanoparticles (Ag-NP) are increasingly used in biomedical applications because of their remarkable antimicrobial activity. In biomedicine, Ag-NP are coated onto or embedded in wound dressings, surgical instruments and bone substitute biomaterials, such as silver-containing calcium phosphate cements. Free Ag-NP and silver ions are released from these coatings or after the degradation of a biomaterial, and may come into close contact with blood cells. Despite the widespread use of Ag-NP as an antimicrobial agent, there is a serious lack of information on the biological effects of Ag-NP on human blood cells. In this study, the uptake of Ag-NP by peripheral monocytes and lymphocytes (T-cells) was analyzed, and the influence of nanosilver on cell biological functions (proliferation, the expression of adhesion molecules, cytokine release and the generation of reactive oxygen species) was studied. After cell culture in the presence of monodispersed Ag-NP (5-30 μg ml -1 silver concentration), agglomerates of nanoparticles were detected within monocytes (CD14+) but not in T-cells (CD3+) by light microscopy, flow cytometry and combined focused ion beam/scanning electron microscopy. The uptake rate of nanoparticles was concentration dependent, and the silver agglomerates were typically found in the cytoplasm. Furthermore, a concentration-dependent activation (e.g. an increased expression of adhesion molecule CD54) of monocytes at Ag-NP concentrations of 10-15 μg ml -1 was observed, and cytotoxicity of Ag-NP-treated monocytes was observed at Ag-NP levels of 25 μg ml -1 and higher. However, no modulation of T-cell proliferation was observed in the presence of Ag-NP. Taken together, our results provide the first evidence for a cell-type-specific uptake of Ag-NP by peripheral blood mononuclear cells (PBMC) and the resultant cellular responses after exposure. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
view abstract doi: 10.1016/j.actbio.2011.05.030 2011 • 47 Characterisation of exosomes derived from human cells by nanoparticle tracking analysis and scanning electron microscopy
Sokolova, V. and Ludwig, A.-K. and Hornung, S. and Rotan, O. and Horn, P.A. and Epple, M. and Giebel, B.
Colloids and Surfaces B: Biointerfaces 87 146-150 (2011)Exosomes from three different cell types (HEK 293T, ECFC, MSC) were characterised by scanning electron microscopy (SEM), dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA). The diameter was around 110. nm for the three cell types. The stability of exosomes was examined during storage at -20 °C, 4 °C, and 37 °C. The size of the exosomes decreased at 4 °C and 37 °C, indicating a structural change or degradation. Multiple freezing to -20 °C and thawing did not affect the exosome size. Multiple ultracentrifugation also did not change the exosome size. © 2011 Elsevier B.V.
view abstract doi: 10.1016/j.colsurfb.2011.05.013 2011 • 46 Element-specific magnetic hysteresis of individual 18 nm Fe nanocubes
Kronast, F. and Friedenberger, N. and Ollefs, K. and Gliga, S. and Tati-Bismaths, L. and Thies, R. and Ney, A. and Weber, R. and Hassel, C. and Römer, F.M. and Trunova, A.V. and Wirtz, C. and Hertel, R. and Dürr, H.A. and Farle, M.
Nano Letters 11 1710-1715 (2011)Correlating the electronic structure and magnetic response with the morphology and crystal structure of the same single ferromagnetic nanoparticle has been up to now an unresolved challenge. Here, we present measurements of the element-specific electronic structure and magnetic response as a function of magnetic field amplitude and orientation for chemically synthesized single Fe nanocubes with 18 nm edge length. Magnetic states and interactions of monomers, dimers, and trimers are analyzed by X-ray photoemission electron microscopy for different particle arrangements. The element-specific electronic structure can be probed and correlated with the changes of magnetic properties. This approach opens new possibilities for a deeper understanding of the collective response of magnetic nanohybrids in multifunctional materials and in nanomagnetic colloidal suspensions used in biomedical and engineering technologies. © 2011 American Chemical Society.
view abstract doi: 10.1021/nl200242c 2011 • 45 Experimental and theoretical studies of the colloidal stability of nanoparticles?a general interpretation based on stability maps
Segets, D. and Marczak, R. and Schäfer, S. and Paula, C. and Gnichwitz, J.-F. and Hirsch, A. and Peukert, W.
ACS Nano 5 4658-4669 (2011)The current work addresses the understanding of the stabilization of nanoparticles in suspension. Specifically, we study ZnO in ethanol for which the influence of particle size and reactant ratio as well as surface coverage on colloidal stability in dependence of the purification progress was investigated. The results revealed that the well-known 〈-potential determines not only the colloidal stability but also the surface coverage of acetate groups bound to the particle surface. The acetate groups act as molecular spacers between the nanoparticles and prevent agglomeration. Next to DLVO calculations based on the theory of Derjaguin, Landau, Verwey and Overbeek using a core-shell model we find that the stability is better understood in terms of dimensionless numbers which represent attractive forces as well as electrostatic repulsion, steric effects, transport properties, and particle concentration. Evaluating the colloidal stability in dependence of time by means of UV-vis absorption measurements a stability map for ZnO is derived. From this map it becomes clear that the dimensionless steric contribution to colloidal stability scales with a stability parameter including dimensionless repulsion and attraction as well as particle concentration and diffusivity of the particles according to a power law with an exponent of ?0.5. Finally, we show that our approach is valid for other stabilizing molecules like cationic dendrons and is generally applicable for a wide range of other material systems within the limitations of vanishing van der Waals forces in refractive index matched situations, vanishing 〈-potential and systems without a stabilizing shell around the particle surface. © 2011 American Chemical Society.
view abstract doi: 10.1021/nn200465b 2011 • 44 Fast and cost-effective purification of gold nanoparticles in the 20-250 nm size range by continuous density gradient centrifugation
Steinigeweg, D. and Schütz, M. and Salehi, M. and Schlücker, S.
Small 7 2443-2448 (2011)A multilayer quasi-continuous density gradient centrifugation method for separating 20-250 nm metal colloids with high size resolution while maintaining particle stability is presented. Colloidal mixtures containing monodisperse gold nanospheres and clusters thereof, in particular, gold dimers, are purified with yields up to 94%. The rapid method uses standard laboratory equipment. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/smll.201100663 2011 • 43 Improvement of the dissolution rate of poorly soluble drugs by solid crystal suspensions
Thommes, M. and Ely, D.R. and Carvajal, M.T. and Pinal, R.
Molecular Pharmaceutics 8 727-735 (2011)We present a novel extrusion based approach where the dissolution rate of poorly soluble drugs (griseofulvin, phenytoin and spironolactone) is significantly accelerated. The drug and highly soluble mannitol are coprocessed in a hot melt extrusion operation. The obtained product is an intimate mixture of the crystalline drug and crystalline excipient, with up to 50% (w/w) drug load. The in vitro drug release from the obtained solid crystalline suspensions is over 2 orders of magnitude faster than that of the pure drug. Since the resulting product is crystalline, the accelerated dissolution rate does not bear the physical stability concerns inherent to amorphous formulations. This approach is useful in situations where the drug is not a good glass former or in cases where it is difficult to stabilize the amorphous drug. Being thermodynamically stable, the dissolution profile and the solid state properties of the product are maintained after storage at 40 °C, 75% RH for at least 90 days. © 2011 American Chemical Society.
view abstract doi: 10.1021/mp1003493 2011 • 42 Influence of individual ionic components on the agglomeration kinetics of silver nanoparticles
Gebauer, J.S. and Treuel, L.
Journal of Colloid and Interface Science 354 546-554 (2011)The precise characteristic of the agglomeration behavior of colloidal suspensions is of paramount interest to many current studies in nanoscience. This work seeks to elucidate the influence that differently charged salts have on the agglomeration state of a Lee-Meisel-type silver colloid. Moreover, we investigate the influence of the chemical nature of individual ions on their potential to induce agglomeration. Raman spectroscopy and surface-enhanced Raman spectroscopy are used to give insights into mechanistic aspects of the agglomeration process and to assess the differences in the influence of different salts on the agglomeration behavior. Finally, we demonstrate the potential of the measurement procedure used in this work to determine the elementary charge on colloidal NPs. © 2010 Elsevier Inc.
view abstract doi: 10.1016/j.jcis.2010.11.016 2011 • 41 Influence of processing time on nanoparticle generation during picosecond-pulsed fundamental and second harmonic laser ablation of metals in tetrahydrofuran
Schwenke, A. and Wagener, P. and Nolte, S. and Barcikowski, S.
Applied Physics A: Materials Science and Processing 104 77-82 (2011)The influence of fundamental and second harmonic wavelength on ablation efficiency and nanoparticle properties is studied during picosecond laser ablation of silver, zinc, and magnesium in polymer-doped tetrahydrofuran. Laser ablation in stationary liquid involves simultaneously the fabrication of nanoparticles by ablation of the target material and fragmentation of dispersed nanoparticles by post irradiation. The ratio in which the laser pulse energy contributes to these processes depends on laser wavelength and colloidal properties. For plasmon absorbers (silver), using the second harmonic wavelength leads to a decrease of the nanoparticle productivity over process time along with exponential decrease in particle diameter, while using the fundamental wavelength results in a constant ablation rate and linear decrease in particle diameter. For colloids made of materials without plasmon absorption (zinc, magnesium), laser scattering is the colloidal property that limits nanoparticle productivity by Mie-scattering of dispersed nanoparticle clusters. © 2011 The Author(s).
view abstract doi: 10.1007/s00339-011-6398-9 2011 • 40 Knowledge-based development of a nitrate-free synthesis route for Cu/ZnO methanol synthesis catalysts via formate precursors
Behrens, M. and Kißner, S. and Girsgdies, F. and Kasatkin, I. and Hermerschmidt, F. and Mette, K. and Ruland, H. and Muhler, M. and Schlögl, R.
Chemical Communications 47 1701-1703 (2011)High-performance Cu/ZnO/(Al2O3) methanol synthesis catalysts are conventionally prepared by co-precipitation from nitrate solutions and subsequent thermal treatment. A new synthesis route is presented, which is based on similar preparation steps and leads to active catalysts, but avoids nitrate contaminated waste water. © 2011 The Royal Society of Chemistry.
view abstract doi: 10.1039/c0cc04933f 2011 • 39 Metal ion release kinetics from nanoparticle silicone composites
Hahn, A. and Brandes, G. and Wagener, P. and Barcikowski, S.
Journal of Controlled Release 154 164-170 (2011)Metal ion release kinetics from silver and copper nanoparticle silicone composites generated by laser ablation in liquids are investigated. The metal ion transport mechanism is studied by using different model equations and their fit to experimental data. Results indicate that during the first 30 days of immersion, Fickian diffusion is the dominant transport mechanism. After this time period, the oxidation and dissolution of nanoparticles from the bulk determine the ion release. This second mechanism is very slow since the dissolution of the nanoparticle is found to be anisotropic. Silver ion release profile is best described by pseudo-first order exponential equation. Copper ion release profile is best described by a second order exponential equation. For practical purposes, the in vitro release characteristics of the bioactive metal ions are evaluated as a function of nanoparticle loading density, the chemistry and the texture of the silicone. Based on the proposed two-step release model, a prediction of the release characteristics over a time course of 84 days is possible and a long-term ion release could be demonstrated. © 2011 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.jconrel.2011.05.023 2011 • 38 Microfluidic emulsion separation - Simultaneous separation and sensing by multilayer nanofilm structures
Uhlmann, P. and Varnik, F. and Truman, P. and Zikos, G. and Moulin, J.-F. and Müller-Buschbaum, P. and Stamm, M.
Journal of Physics Condensed Matter 23 (2011)Emulsion separation is of high relevance for filtration applications, liquid-liquid-partitioning of biomolecules like proteins and recovery of products from droplet microreactors. Selective interaction of various components of an emulsion with substrates is used to design microfluidic flow chambers for efficient separation of emulsions into their individual components. Our lab-on-a-chip device consists of an emulsion separation cell with an integrated silicon sensor chip, the latter allowing the detection of liquid motion via the field-effect signal. Thus, within our lab-on-a-chip device, emulsions can be separated while the separation process is monitored simultaneously. For emulsion separation a surface energy step gradient, namely a sharp interface between the hydrophobic and hydrophilic parts of the separation chamber, is used. The key component of the lab-on-a-chip system is a multilayer and multifunctional nanofilm structure which not only provides the surface energy step gradient for emulsion separation but also constitutes the functional parts of the field-effect transistors. The proof-of-principle was performed using a model emulsion consisting of immiscible aqueous and organic solvent components. Droplet coalescence was identified as a key aspect influencing the separation process, with quite different effects during separation on open surfaces as compared to slit geometry. For a detailed description of this observation, an analytical model was derived and lattice Boltzmann computer simulations were performed. By use of grazing incidence small angle x-ray scattering (GISAXS) interfacial nanostructures during gold nanoparticle deposition in a flow field were probed to demonstrate the potential of GISAXS for insitu investigations during flow. © 2011 IOP Publishing Ltd.
view abstract doi: 10.1088/0953-8984/23/18/184123 2011 • 37 Morphology and photoluminescence study of titania nanoparticles
Memesa, M. and Lenz, S. and Emmerling, S.G.J. and Nett, S. and Perlich, J. and Müller-Buschbaum, P. and Gutmann, J.S.
Colloid and Polymer Science 289 943-953 (2011)Titania nanoparticles are prepared by sol-gel chemistry with a poly(ethylene oxide) methyl ether methacrylate-block-poly(dimethylsiloxane)- block-poly(ethylene oxide) methyl ether methacrylate triblock copolymer acting as the templating agent. The sol-gel components-hydrochloric acid, titanium tetraisopropoxide, and triblock copolymer-are varied to investigate their effect on the resulting titania morphology. An increased titania precursor or polymer content yields smaller primary titania structures. Microbeam grazing incidence small-angle X-ray scattering measurements, which are analyzed with a unified fit model, reveal information about the titania structure sizes. These small structures could not be observed via the used microscopy techniques. The interplay among the sol-gel components via our triblock copolymer results in different sized titania nanoparticles with higher packing densities. Smaller sized titania particles, (∼13-20 nm in diameter) in the range of exciton diffusion length, are formed by 2% by weight polymer and show good crystallinity with less surface defects and high oxygen vacancies. © 2011 The Author(s).
view abstract doi: 10.1007/s00396-011-2421-0 2011 • 36 Nanoparticle exposure at nanotechnology workplaces: A review
Kuhlbusch, T.A.J. and Asbach, C. and Fissan, H. and Göhler, D. and Stintz, M.
Particle and Fibre Toxicology 8 (2011)Risk, associated with nanomaterial use, is determined by exposure and hazard potential of these materials. Both topics cannot be evaluated absolutely independently. Realistic dose concentrations should be tested based on stringent exposure assessments for the corresponding nanomaterial taking into account also the environmental and product matrix. This review focuses on current available information from peer reviewed publications related to airborne nanomaterial exposure. Two approaches to derive realistic exposure values are differentiated and independently presented; those based on workplace measurements and the others based on simulations in laboratories. An assessment of the current available workplace measurement data using a matrix, which is related to nanomaterials and work processes, shows, that data are available on the likelihood of release and possible exposure. Laboratory studies are seen as an important complementary source of information on particle release processes and hence for possible exposure. In both cases, whether workplace measurements or laboratories studies, the issue of background particles is a major problem. From this review, major areas for future activities and focal points are identified. © 2011 Kuhlbusch et al; licensee BioMed Central Ltd.
view abstract doi: 10.1186/1743-8977-8-22 2011 • 35 Pitfalls in the characterization of nanoporous and nanosized materials
Nanoscale 3 792-810 (2011)With the advent of highly sophisticated analytical tools, numerous physical methods are nowadays available for comprehensive characterization of inorganic matter and, as special cases, of porous and nanosized materials. Intelligent experimental setup and correct evaluation of the experimental data can provide helpful insights into the chemical and physical properties of such materials. However, scanning of literature reports shows that in many cases evaluation and interpretation of experimental data are erroneous. As a result, the description of a new material can be useless or even worse, misleading. Wrong evaluation is even more critical if mechanistic theories are based on such data. Characterization of porous and/or nanosized materials is mainly performed by gas adsorption, X-ray powder diffraction, electron microscopy and surface spectroscopy. For correct interpretation of experimental data one should be aware of certain pitfalls. The present paper summarizes prominent faults and may show how they can be avoided. It is supposed to provide some hand-on knowledge on correct analysis of materials. Addressed are primarily non-experts and researchers being new to the field of characterization of inorganic nanosized or nanoporous materials. © 2011 The Royal Society of Chemistry.
view abstract doi: 10.1039/c0nr00561d 2011 • 34 Plasmonically active micron-sized beads for integrated solid-phase synthesis and label-free SERS analysis
Gellner, M. and Niebling, S. and Kuchelmeister, H.Y. and Schmuck, C. and Schlücker, S.
Chemical Communications 47 12762-12764 (2011)Self-assembly of gold nanospheres with a very thin glass shell onto the surface of beads yields a plasmonically active micron-sized substrate for integrated solid-phase synthesis and label-free SERS analysis. The proof-of-principle of this approach is demonstrated by the vibrational spectroscopic discrimination of three distinct amino acids and a dipeptide. © 2011 The Royal Society of Chemistry.
view abstract doi: 10.1039/c1cc13562g 2011 • 33 Possibilities and limitations of different analytical methods for the size determination of a bimodal dispersion of metallic nanoparticles
Mahl, D. and Diendorf, J. and Meyer-Zaika, W. and Epple, M.
Colloids and Surfaces A: Physicochemical and Engineering Aspects 377 386-392 (2011)Silver nanoparticles (about 70. nm) and gold nanoparticles (about 15. nm) were prepared and colloidally stabilized with poly(vinylpyrrolidone) (PVP). The pure nanoparticles as well as a 1:1 mixture (w:w) were analysed with a variety of methods which probe the size distribution: Scanning electron microscopy, transmission electron microscopy, dynamic light scattering, analytical disc centrifugation, and Brownian motion analysis (nanoparticle tracking analysis). The differences between the methods are highlighted and their ability to distinguish between silver and gold nanoparticles in the mixture is demonstrated. The size distribution data from the different methods were clearly different, therefore it is recommended to apply more than one method to characterize the nanoparticle dispersion. In particular, the smaller particles were undetectable by dynamic light scattering and nanoparticle tracking analysis in the presence of the large particles. For the 1:1 mixture, only electron microscopy and analytical disc centrifugation were able to give quantitative data on the size distribution. On the other hand, it is not possible to make statements about an agglomeration in dispersion with electron microscopy because an agglomeration may also have occurred during the drying process. © 2011 Elsevier B.V.
view abstract doi: 10.1016/j.colsurfa.2011.01.031 2011 • 32 Quantitative measurements of magnetic stray field dynamics of Permalloy particles in a photoemission electron microscopy
Nepijko, S.A. and Krasyuk, A. and Oelsner, A. and Schneider, C. M. and Schönhense, G.
Journal of Microscopy 242 216-220 (2011)By example of a Permalloy particle (40 × 40 μm 2 size, 30 nm thickness) we demonstrate a procedure to quantitatively investigate the dynamics of magnetic stray fields during ultrafast magnetization reversal. The measurements have been performed in a time-resolving photoemission electron microscope using the X-ray magnetic circular dichroism. In the particle under investigation, we have observed a flux-closure-dominated magnetic ground structure, minimizing the magnetic stray field outside the sample. A fast magnetic field pulse introduced changes in the micromagnetic structure accompanied with an incomplete flux closure. As a result, stray fields arise along the edges of domains, which cause a change of contrast and an image deformation of the particles geometry (curvature of its edge). The magnetic stray fields are calculated from a deformation of the X-ray magnetic circular dichroism (XMCD) images taken after the magnetic field pulse in a 1 ns interval. These measurements reveal a decrease of magnetic stray fields with time. An estimate of the lower limit of the domain wall velocity yields about 2 × 10 3 m s -1. © 2010 The Authors Journal of Microscopy © 2010 Royal Microscopical Society.
view abstract doi: 10.1111/j.1365-2818.2010.03472.x 2011 • 31 Real-space imaging of inelastic Friedel-like surface oscillations emerging from molecular adsorbates
Gawronski, H. and Fransson, J. and Morgenstern, K.
Nano Letters 11 2720-2724 (2011)We report real space imaging measurements of inelastic Friedel oscillations. The inelastic electron tunneling spectroscopy, using scanning tunneling microscopy, around dimers of dichlorobenze adsorbates on Au(111) surface display clear spatial modulations that we attribute to inelastic scattering at the molecular sites caused by molecular vibrations. Due to local interactions between the adsorbate and the surface states, the molecular vibrations generate a redistribution of the charge density at energies in a narrow range around the inelastic mode. Our experimental findings are supported by theoretical arguments. © 2011 American Chemical Society.
view abstract doi: 10.1021/nl201076g 2011 • 30 Stability and dynamics of droplets on patterned substrates: Insights from experiments and lattice Boltzmann simulations
Varnik, F. and Gross, M. and Moradi, N. and Zikos, G. and Uhlmann, P. and Müller-Buschbaum, P. and Magerl, D. and Raabe, D. and Steinbach, I. and Stamm, M.
Journal of Physics Condensed Matter 23 (2011)The stability and dynamics of droplets on solid substrates are studied both theoretically and via experiments. Focusing on our recent achievements within the DFG-priority program 1164 (Nano-and Microfluidics), we first consider the case of (large) droplets on the so-called gradient substrates. Here the term gradient refers to both a change of wettability (chemical gradient) or topography (roughness gradient). While the motion of a droplet on a perfectly flat substrate upon the action of a chemical gradient appears to be a natural consequence of the considered situation, we show that the behavior of a droplet on a gradient of topography is less obvious. Nevertheless, if care is taken in the choice of the topographic patterns (in order to reduce hysteresis effects), a motion may be observed. Interestingly, in this case, simple scaling arguments adequately account for the dependence of the droplet velocity on the roughness gradient (Moradi et al 2010 Europhys. Lett. 8926006). Another issue addressed in this paper is the behavior of droplets on hydrophobic substrates with a periodic arrangement of square shaped pillars. Here, it is possible to propose an analytically solvable model for the case where the droplet size becomes comparable to the roughness scale (Gross et al 2009 Europhys. Lett. 8826002). Two important predictions of the model are highlighted here. (i)There exists a state with a finite penetration depth, distinct from the full wetting (Wenzel) and suspended (Cassie-Baxter, CB) states. (ii)Upon quasi-static evaporation, a droplet initially on the top of the pillars (CB state) undergoes a transition to this new state with a finite penetration depth but then (upon further evaporation) climbs up the pillars and goes back to the CB state again. These predictions are confirmed via independent numerical simulations. Moreover, we also address the fundamental issue of the internal droplet dynamics and the terminal center of mass velocity on a flat substrate. © 2011 IOP Publishing Ltd.
view abstract doi: 10.1088/0953-8984/23/18/184112 2011 • 29 Stoichiometry of alloy nanoparticles from laser ablation of PtIr in acetone and their electrophoretic deposition on PtIr electrodes
Jakobi, J. and Menéndez-Manjón, A. and Chakravadhanula, V.S.K. and Kienle, L. and Wagener, P. and Barcikowski, S.
Nanotechnology 22 (2011)Charged Pt-Ir alloy nanoparticles are generated through femtosecond laser ablation of a Pt9Ir target in acetone without using chemical precursors or stabilizing agents. Preservation of the target's stoichiometry in the colloidal nanoparticles is confirmed by transmission electron microscopy (TEM)-energy-dispersive x-ray spectroscopy (EDX), high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM)-EDX elemental maps, high resolution TEM and selected area electron diffraction (SAED) measurements. Results are discussed with reference to thermophysical properties and the phase diagram. The nanoparticles show a lognormal size distribution with a mean Feret particle size of 26nm. The zeta potential of - 45mV indicates high stability of the colloid with a hydrodynamic diameter of 63nm. The charge of the particles enables electrophoretic deposition of nanoparticles, creating nanoscale roughness on three-dimensional PtIr neural electrodes within a minute. In contrast to coating with Pt or Ir oxides, this method allows modification of the surface roughness without changing the chemical composition of PtIr. © 2011 IOP Publishing Ltd.
view abstract doi: 10.1088/0957-4484/22/14/145601 2011 • 28 Structural and magnetic characterization of self-assembled iron oxide nanoparticle arrays
Benitez, M.J. and Mishra, D. and Szary, P. and Badini Confalonieri, G.A. and Feyen, M. and Lu, A.H. and Agudo, L. and Eggeler, G. and Petracic, O. and Zabel, H.
Journal of Physics Condensed Matter 23 (2011)We report about a combined structural and magnetometric characterization of self-assembled magnetic nanoparticle arrays. Monodisperse iron oxide nanoparticles with a diameter of 20nm were synthesized by thermal decomposition. The nanoparticle suspension was spin-coated on Si substrates to achieve self-organized arrays of particles and subsequently annealed at various conditions. The samples were characterized by x-ray diffraction, and bright and dark field high resolution transmission electron microscopy. The structural analysis is compared to magnetization measurements obtained by superconducting quantum interference device magnetometry. We can identify either multi-phase FexO/γ-Fe2O3 or multi-phase Fe xO/Fe3O4 nanoparticles. The Fe xO/γ-Fe2O3 system shows a pronounced exchange bias effect which explains the peculiar magnetization data found for this system. © 2011 IOP Publishing Ltd.
view abstract doi: 10.1088/0953-8984/23/12/126003 2011 • 27 Structure and flow of droplets on solid surfaces
Müller-Buschbaum, P. and Magerl, D. and Hengstler, R. and Moulin, J.-F. and Körstgens, V. and Diethert, A. and Perlich, J. and Roth, S.V. and Burghammer, M. and Riekel, C. and Gross, M. and Varnik, F. and Uhlmann, P. and Stamm, ...
Journal of Physics Condensed Matter 23 (2011)The structure and flow of droplets on solid surfaces is investigated with imaging and scattering techniques and compared to simulations. To access nanostructures at the liquid-solid interface advanced scattering techniques such as grazing incidence small-angle x-ray scattering (GISAXS) with micro-and nanometer-sized beams, GISAXS and insitu imaging ellipsometry and GISAXS tomography are used. Using gold nanoparticle suspensions, structures observed in the wetting area due to deposition are probed insitu during the drying of the droplets. After drying, nanostructures in the wetting area and inside the dried droplets are monitored. In addition to drying, a macroscopic movement of droplets is caused by body forces acting on an inclined substrate. The complexity of the solid surfaces is increased from simple silicon substrates to binary polymer brushes, which undergo a switching due to the liquid in the droplet. Nanostructures introduced in the polymer brush due to the movement of droplets are observed. © 2011 IOP Publishing Ltd.
view abstract doi: 10.1088/0953-8984/23/18/184111 2011 • 26 Supramolecular structures: Robust materials from weak forces
Nature Nanotechnology 6 136-137 (2011)
doi: 10.1038/nnano.2011.28 2011 • 25 Thermal stability of TiAIN/CrN multilayer coatings studied by atom probe tomography
Choi, P.-P. and Povstugar, I. and Ahn, J.-P. and Kostka, A. and Raabe, D.
Ultramicroscopy 111 518-523 (2011)This study is about the microstructural evolution of TiAlN/CrN multilayers (with a Ti:Al ratio of 0.75:0.25 and average bilayer period of 9 nm) upon thermal treatment. Pulsed laser atom probe analyses were performed in conjunction with transmission electron microscopy and X-ray diffraction. The layers are found to be thermally stable up to 600 °C. At 700 °C TiAlN layers begin to decompose into Ti- and Al-rich nitride layers in the out-of-plane direction. Further increase in temperature to 1000 °C leads to a strong decomposition of the multilayer structure as well as grain coarsening. Layer dissolution and grain coarsening appear to begin at the surface. Domains of AlN and TiCrN larger than 100 nm are found, together with smaller nano-sized AlN precipitates within the TiCrN matrix. Fe and V impurities are detected in the multilayers as well, which diffuse from the steel substrate into the coating along columnar grain boundaries. © 2010 Elsevier B.V.
view abstract doi: 10.1016/j.ultramic.2010.11.012 2011 • 24 Thermodynamics and molecular dynamics investigation of a possible new critical size for surface and inner cohesive energy of Al nanoparticles
Chamaani, A. and Marzbanrad, E. and Rahimipour, M. R. and Yaghmaee, M. S. and Aghaei, A. and Kamachali, R. D. and Behnamian, Y.
Journal of Nanoparticle Research 13 6059--6067 (2011)In this study, the authors first review the previously developed, thermodynamics-based theory for size dependency of the cohesion energy of free-standing spherically shaped Al nanoparticles. Then, this model is extrapolated to the cubic and truncated octahedron Al nanoparticle shapes. A series of computations for Al nanoparticles with these two new shapes are presented for particles in the range of 1-100 nm. The thermodynamics computational results reveal that there is a second critical size around 1.62 and 1 nm for cubes and truncated octahedrons, respectively. Below this critical size, particles behave as if they consisted only of surface-energy-state atoms. A molecular dynamics simulation is used to verify this second critical size for Al nanoparticles in the range of 1-5 nm. MD simulation for cube and truncated octahedron shapes shows the second critical point to be around 1.63 and 1.14 nm, respectively. According to the modeling and simulation results, this second critical size seems to be a material property characteristic rather than a shape-dependent feature.
view abstract doi: 10.1007/s11051-011-0258-6 2011 • 23 Tracer percentage prediction of dive reflex samplers
Bensmann, S. and Lockow, E. and Walzel, P. and Weihs, C.
Powder Technology 208 63-71 (2011)Instead of the frequently applied monochromatic light probes a whie light fibre optic system was employed at the Laboratory of Mechanical Process Design, TU Dortmund University, in order to exploit the color in formations for concentration measurements within bulk solid. The system is applied to obtain local particle concentrations of blue- and red-colored quartz sand within the bed of a rotary drum. 16 solid mixtures with one or two particle sizes from 100 μm to 2000 μm and different species concentration were analyzed and the relationship between probe measurement values and red sand content was determined by statistical regression methods. After transformation of the data, linear models were found to derive the red sand content from given measurement values. Based thereupon, an all-purpose scheme for mono- and bi-disperse solid mixtures was developed and verified in an example with a mean error of 5%. © 2010 Elsevier B.V.
view abstract doi: 10.1016/j.powtec.2010.12.004 2010 • 22 A European aerosol phenomenology - 3: Physical and chemical characteristics of particulate matter from 60 rural, urban, and kerbside sites across Europe
Putaud, J.-P. and Van Dingenen, R. and Alastuey, A. and Bauer, H. and Birmili, W. and Cyrys, J. and Flentje, H. and Fuzzi, S. and Gehrig, R. and Hansson, H.C. and Harrison, R.M. and Herrmann, H. and Hitzenberger, R. and Hüglin, C...
Atmospheric Environment 44 1308-1320 (2010)This paper synthesizes data on aerosol (particulate matter, PM) physical and chemical characteristics, which were obtained over the past decade in aerosol research and monitoring activities at more than 60 natural background, rural, near-city, urban, and kerbside sites across Europe. The data include simultaneously measured PM10 and/or PM2.5 mass on the one hand, and aerosol particle number concentrations or PM chemistry on the other hand. The aerosol data presented in our previous works (Van Dingenen et al., 2004; Putaud et al., 2004) were updated and merged to those collected in the framework of the EU supported European Cooperation in the field of Scientific and Technical action COST633 (Particulate matter: Properties related to health effects). A number of conclusions from our previous studies were confirmed. There is no single ratio between PM2.5 and PM10 mass concentrations valid for all sites, although fairly constant ratios ranging from 0.5 to 0.9 are observed at most individual sites. There is no general correlation between PM mass and particle number concentrations, although particle number concentrations increase with PM2.5 levels at most sites. The main constituents of both PM10 and PM2.5 are generally organic matter, sulfate and nitrate. Mineral dust can also be a major constituent of PM10 at kerbside sites and in Southern Europe. There is a clear decreasing gradient in SO4 2- and NO3 - contribution to PM10 when moving from rural to urban to kerbside sites. In contrast, the total carbon/PM10 ratio increases from rural to kerbside sites. Some new conclusions were also drawn from this work: the ratio between ultrafine particle and total particle number concentration decreases with PM2.5 concentration at all sites but one, and significant gradients in PM chemistry are observed when moving from Northwestern, to Southern to Central Europe. Compiling an even larger number of data sets would have further increased the significance of our conclusions, but collecting all the aerosol data sets obtained also through research projects remains a tedious task. © 2009 Elsevier Ltd. All rights reserved.
view abstract doi: 10.1016/j.atmosenv.2009.12.011 2010 • 21 An aqueous emulsion route to synthesize mesoporous carbon vesicles and their nanocomposites
Gu, D. and Bongard, H. and Deng, Y. and Feng, D. and Wu, Z. and Fang, Y. and Mao, J. and Tu, B. and Schüth, F. and Zhao, D.
Advanced Materials 22 833-837 (2010)Onionlike mesoporous carbon and carbonsilica nanocomposites with multilayer vesicle structures can be synthesized by an organic-inorganic co-assembly method under hydrothermal conditions in an aqueous emulsion solution (see figure). The nanocomposite vesicles have ordered lamellar mesostructures with about 3-9 layers and carbon pillars are located between the neighboring shells. (Chemical Equation Persentation). © 2010 WILEY-VCH Verlag GmbH & Co. KGaA.
view abstract doi: 10.1002/adma.200902550 2010 • 20 An experimental analysis on mixing and stoking of monodisperse spheres on a grate
Sudbrock, F. and Simsek, E. and Wirtz, S. and Scherer, V.
Powder Technology 198 29-37 (2010)A better understanding of the mixing and stoking process is crucial for an optimization of the combustion process on grate firing systems. Thus experimental studies were carried out to analyse the response of a particle assembly on varying grate operational parameters. To reduce the number of variables which affect the system a generic grate design was chosen and a material of monodisperse spheres was selected. The grate system applied uses vertically moving parallel bars to induce mixing. Different patterns of bar motion were created by linking the bars in groups of uniform movement. A transparent polycarbonate side wall gives optical access to front layer of spheres. The mixing process was measured and quantified by image analysis of this visible layer. When applying a constant number of bar strokes it is found that the mixing performance is independent of the bar velocity. However, mixing performance increases nearly linearly with the stroke length. It turned out that specific "movement patterns" could be identified which show improved mixing behaviour. The results provided here may also be used for comparison with simulations of the particle mixing with the Discrete Element Method (DEM). © 2009 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.powtec.2009.10.011 2010 • 19 Biocompatibility evaluation of nano-rod hydroxyapatite/gelatin coated with nano-HAp as a novel scaffold using mesenchymal stem cells
Zandi, M. and Mirzadeh, H. and Mayer, C. and Urch, H. and Eslaminejad, M.B. and Bagheri, F. and Mivehchi, H.
Journal of Biomedical Materials Research - Part A 92 1244-1255 (2010)This study is devoted to fabricate a novel hydroxyapatite(HAp)/gelatin scaffold coated with nano-HAp in nano-rod configuration to evaluate its biocompatibility potential. The nano-HAp particles are needle and rod-like with widths ranging between 30 to 60 nm and lengths from 100 to 300 nm, respectively. Because of their higher surface area and higher reactivity, the nano-rod particles were distributed in gelatin much better than spherical and mixed shapes particles. The compressive modulus of the nano-HAp/gelatin scaffolds coated with nano-HAp was comparable with the compressive modulus of a human cancellous bone. The potential performance of the fabricated scaffolds as seeding media was assayed using mesenchymal stem cells (MSCs). MTT (3-(4,5-dimethylthiazol-2-yl)-1,5-diphenyl tetrazulium bromide) assays were performed on days 4 and 7 and the number of the cells per scaffold was determined. On the basis of this assay, all the studied scaffolds exhibited an appropriate environment in which the loaded cells appeared to be proliferated during the cultivation periods. In all fabricated composite scaffolds, marrow-derived MSCs appeared to occupy the scaffolds internal spaces and attach on their surfaces. According to the cell culture experiments, the incorporation of rod-like nano-HAp and coating of scaffolds with nano-HAp particles enabled the prepared scaffolds to possess desirable biocompatibility, high bioactivity, and sufficient mechanical strength in comparison with noncoated HAp samples. This research suggests that the newly developed scaffold has a potential as a suitable scaffold for bone tissue engineering. © 2009 Wiley Periodicals, Inc.
view abstract doi: 10.1002/jbm.a.32452 2010 • 18 Biocompatibility of nanoactuators: Stem cell growth on laser-generated nickel-titanium shape memory alloy nanoparticles
Barcikowski, S. and Hahn, A. and Guggenheim, M. and Reimers, K. and Ostendorf, A.
Journal of Nanoparticle Research 12 1733-1742 (2010)Nanoactuators made from nanoparticulate NiTi shape memory alloy show potential in the mechanical stimulation of bone tissue formation from stem cells. We demonstrate the fabrication of Ni, Ti, and NiTi shape memory alloy nanoparticles and their biocompatibility to human adipose-derived stem cells. The stoichiometry and phase transformation property of the bulk alloy is preserved during attrition by femtosecond laser ablation in liquid, giving access to colloidal nanoactuators. No adverse effect on cell growth and attachment is observed in proliferation assay and environmental electron scanning microscopy, making this material attractive for mechanical stimulation of stem cells.
view abstract doi: 10.1007/s11051-009-9834-4 2010 • 17 Discharge cavitation during microwave electrochemistry at micrometre-sized electrodes
Rassaei, L. and Nebel, M. and Rees, N.V. and Compton, R.G. and Schuhmann, W. and Marken, F.
Chemical Communications 46 812-814 (2010)Microwave induced activation of electrochemical processes at microelectrodes (ca. 0.8 m diameter) immersed in aqueous electrolyte media is shown to be driven by (i) continuous stable cavitation (giving rise to Faradaic current enhancements by up to three orders of magnitude) and (ii) transient discharge cavitation on the s timescale (giving rise to cathodic plasma current spikes and more violent surface erosion effects). © 2010 The Royal Society of Chemistry.
view abstract doi: 10.1039/b920154h 2010 • 16 Electrochemical synthesis of core-shell catalysts for electrocatalytic applications
Kulp, C. and Chen, X. and Puschhof, A. and Schwamborn, S. and Somsen, C. and Schuhmann, W. and Bron, M.
ChemPhysChem 11 2854-2861 (2010)A novel electrochemical method to prepare platinum shells around carbon-supported metal nanoparticles (Ru and Au) by pulsed electrodeposition from solutions containing Pt ions is presented. Shell formation is confirmed by characteristic changes in the cyclic voltammograms, and is further evidenced by monitoring particle growth by transmission electron microscopy as well as by energy-dispersive analysis of X rays (EDX). Scanning electrochemical microscopy and EDX measurements indicate a selective Pt deposition on the metal/carbon catalyst, but not on the glassy carbon substrate. The thus prepared carbon-supported core-shell nanoparticles are investigated with regard to their activity in electrocatalytic oxygen reduction, which demonstrates the applicability of these materials in electrocatalysis or sensors. © 2010 Wiley-VCH Verlag GmbH& Co. KGaA, Weinheim.
view abstract doi: 10.1002/cphc.200900881 2010 • 15 Ex-post size control of high-temperature-stable yolk-shell Au,@ZrO 2 catalysts
Güttel, R. and Paul, M. and Schüth, F.
Chemical Communications 46 895-897 (2010)Yolk-shell catalysts have attracted interest in both academia and industry, since they combine high-temperature stability with a reduced complexity for kinetic and mechanistic investigations. This contribution presents a possibility to adjust the size of an active gold core inside a porous zirconia shell via an ex-post-modification approach. © The Royal Society of Chemistry 2010.
view abstract doi: 10.1039/b921792d 2010 • 14 Identification of magnetic properties of few nm sized FePt crystalline particles by characterizing the intrinsic atom order using aberration corrected S/TEM
Biskupek, J. and Jinschek, J.R. and Wiedwald, U. and Bendele, M. and Han, L. and Ziemann, P. and Kaiser, U.
Ultramicroscopy 110 820-825 (2010)Hard-magnetic nanomaterials like nanoparticles of FePt are of great interest because of their promising potential for data storage applications. The magnetic properties of FePt structures strongly differ whether the crystal phases are face centered cubic (fcc) or face centered tetragonal (fct). We evaluated aberration corrected HRTEM, electron diffraction and aberration corrected HAADF-STEM as methods to measure the chemical degree of order S that describes the ordering of Pt and Fe atoms within the crystals unit cells. S/TEM experiments are accompanied by image calculations. The findings are compared with results obtained from X-ray diffraction on a FePt film. Our results show that STEM is a reasonable fast approach over HRTEM and electron diffraction to locally determine the chemical degree of order S. © 2010 Elsevier B.V.
view abstract doi: 10.1016/j.ultramic.2010.02.043 2010 • 13 Magnetic alloy nanoparticles from laser ablation in cyclopentanone and their embedding into a photoresist
Jakobi, J. and Petersen, S. and Menéndez-Manjón, A. and Wagener, P. and Barcikowski, S.
Langmuir 26 6892-6897 (2010)The generation of nonoxidized magnetic alloy nanoparticles is still a challenge using conventional chemical reduction methods. However, because these nanoparticles are currently attracting much attention, alternative methods are required. In this context, the applicability of femtosecond laser ablation, which has evolved as a powerful tool for the generation of colloidal metal nanoparticles, has been investigated using the example of Ni48Fe 52 and Sm2Co17 ablation in cyclopentanone. Besides stability and size measurements, the focus has been placed on the analysis of the elemental composition of nanoparticles, which proved the preservation of the stoichiometry of the target in Ni-Fe nanoparticles but not in Sm-Co. It is assumed that this is due to a greater difference in the heat of evaporation of the bulk alloy components in Sm-Co than in Ni-Fe. Hence, the successful generation of magnetic alloy nanoparticles is possible for alloys composed of elements with similar heats of evaporation. This one-step approach allows the fabrication of nanomagnetic polymer composites (e.g., with application prospects in microtechnology such as microactuators). © 2010 American Chemical Society.
view abstract doi: 10.1021/la101014g 2010 • 12 New insights into the pelletization mechanism by extrusion/spheronization
Koester, M. and Thommes, M.
AAPS PharmSciTech 11 1549-1551 (2010)Pellet manufacturing by extrusion/spheronization is quite common in the pharmaceutical field because the obtained product is characterized by a high sphericity as well as a narrow particle size distribution. The established mechanisms only consider deformation of the initially fractured particles but do not account for mass transfer between the particles as a factor in achieving spherical particles. This study dealt with the visualization of mass transfer during spheronization. Therefore, two common pelletization aids, microcrystalline cellulose and kappa-carrageenan, were used alone as well as in combination with lactose as a filler. This study proves that mass transfer between particles must be considered in addition to plastic deformation in order to capture the spheronization mechanism. Moreover, it is evident that there are regional distinctions in the amount of mass transfer at the particle surface. Therefore, the commonly espoused pelletization mechanisms need to be extended to account for material transfer between pellet particles, which has not been considered before. © 2010 American Association of Pharmaceutical Scientists.
view abstract doi: 10.1208/s12249-010-9532-7 2010 • 11 Observation of breathing-like modes in an individual multiwalled carbon nanotube
Spudat, C. and Müller, M. and Houben, L. and Maultzsch, J. and Goss, K. and Thomsen, C. and Schneider, C.M. and Meyer, C.
Nano Letters 10 4470-4474 (2010)We study collective vibrational breathing modes in the Raman spectrum of a multiwalled carbon nanotube. In correlation with high-resolution transmission electron microscopy, we find that these modes have energies differing by more than 23% from the radial breathing modes of the corresponding single-walled nanotubes. This shift in energy is explained with intershell interactions using a model of coupled harmonic oscillators. The strength of this interaction is related to the coupling strength expected for few-layer graphene. © 2010 American Chemical Society.
view abstract doi: 10.1021/nl102305a 2010 • 10 Orthogonal protein decoration of DNA origami
Saccà, B. and Meyer, R. and Erkelenz, M. and Kiko, K. and Arndt, A. and Schroeder, H. and Rabe, K.S. and Niemeyer, C.M.
Angewandte Chemie - International Edition 49 9378-9383 (2010)If the face fits: Self-labeling fusion proteins have been used for the site-specific decoration of DNA origami. This method even allows individual faces of the quasi-two-dimensional plane of the nanostructure to be specifically decorated (see picture), thereby enabling directional immobilization and thus control over the accessibility of distinct proteins presented on the structure. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/anie.201005931 2010 • 9 Perfluorocarbon-filled poly(lactide-co-gylcolide) nano- and microcapsules as artificial oxygen carriers for blood substitutes: A physico-chemical assessment
Bauer, J. and Zähres, M. and Zellermann, A. and Kirsch, M. and Petrat, F. and De Groot, H. and Mayer, C.
Journal of Microencapsulation 27 122-132 (2010)The physico-chemical suitability of perfluorocarbon-filled capsules as artificial oxygen carriers for blood substitutes is assessed on the example of biodegradable poly(lactide-co-gylcolide) micro- and nanocapsules with a liquid content of perfluorodecalin. The morphology of the capsules is studied by confocal laser scanning microscopy using Nile red as a fluorescent marker. The mechanical stability and the wall flexibility of the capsules are examined by atomic force microscopy. The permeability of the capsule walls in connection with the oxygen uptake is detected by nuclear magnetic resonance. It is shown that the preparation in fact leads to nanocapsules with a mechanical stability which compares well with the one of red blood cells. The capsule walls exhibit sufficient permeability to allow for the exchange of oxygen in aqueous environment. In the fully saturated state, the amount of oxygen dissolved within the encapsulated perfluorodecalin in aqueous dispersion is as large as for bulk perfluorodecalin. Simple kinetic studies are presently restricted to the time scale of minutes, but so far indicate that the permeability of the capsule walls could be sufficient to allow for rapid gas exchange.
view abstract doi: 10.3109/02652040903052002 2010 • 8 Quantitative visualization of colloidal and intracellular gold nanoparticles by confocal microscopy
Klein, S. and Petersen, S. and Taylor, U. and Rath, D. and Barcikowski, S.
Journal of Biomedical Optics 15 (2010)Gold nanoparticles (AuNPs) have the potential to become a versatile biomarker. For further use of AuNPs labeled with functionalized molecules, their visualization in biological systems by routine laboratory tools such as light microscopy is crucial. However, the size far below the diffraction limit affords specialized parameters for microscopical detection, which stimulated the current study, aimed to determine from which size onward AuNPs, either in dispersion or cell-associated, can be reliably detected by standard confocal microscopy. First, gold colloids of size-restricted fractions are examined in dispersion. At a minimum particle size of 60 nm, detection appears to be reliable. Particle counts in dilution series confirm these results by revealing single particle detection of 60-nm colloids. Second, AuNPs are visualized and quantified in cells, which interestingly cause a phase shift in the reflection of AuNPs. Gold mass spectroscopy confirms the number of AuNPs counted microscopically inside cells. Furthermore, it demonstrates for the first time a very high diffusion rate of 15-nm particles into the cells. In conclusion, the results back the suitability of confocal microscopy for the quantitative tracking of colloidal and intracellular gold nanoparticles sized 60 nm. © 2010 Society of Photo-Optical Instrumentation Engineers.
view abstract doi: 10.1117/1.3461170 2010 • 7 Small-sized HZSM-5 zeolite as highly active catalyst for gas phase dehydration of glycerol to acrolein
Jia, C.-J. and Liu, Y. and Schmidt, W. and Lu, A.-H. and Schüth, F.
Journal of Catalysis 269 71-79 (2010)The catalytic properties of nanocrystalline HZSM-5 catalysts with high Si/Al molar ratio (ca. 65) were investigated in the gas phase dehydration of aqueous glycerol. Compared with bulk HZSM-5, the small-sized catalyst exhibits greatly enhanced catalytic performance in glycerol dehydration even with very high GHSV (=1438 h -1). Catalysts with different Si/Al ratios were studied, but it is difficult to separate the influence of Si/Al ratio from that of particle size. However, by varying the proton exchange degree for one mother batch of zeolite, a series of H xNa 1-xZSM-5 catalysts with same particle size and different Brønsted acid site densities was prepared. The catalytic results for this series of samples show that high density of Brønsted acid sites favors the production of acrolein. Based on these results, small-sized HZSM-5 with high aluminum content appears to be most promising for gas phase dehydration of glycerol. © 2009 Elsevier Inc. All rights reserved.
view abstract doi: 10.1016/j.jcat.2009.10.017 2010 • 6 Support effects in the Au-catalyzed CO oxidation - Correlation between activity, oxygen storage capacity, and support reducibility
Widmann, D. and Liu, Y. and Schüth, F. and Behm, R.J.
Journal of Catalysis 276 292-305 (2010)The oxygen storage capacity (OSC) and its correlation with the activity for the CO oxidation reaction and the reducibility of the support material were investigated for four different metal oxide-supported Au catalysts with similar Au loading and Au particle sizes (Au/Al2O3, Au/TiO 2, Au/ZnO, Au/ZrO2), which were prepared by deposition of pre-formed Au colloids. Temporal Analysis of Products (TAP) reactor measurements show that the OSC and the activity for CO oxidation, measured under identical conditions, differ significantly for these catalysts and are correlated with each other and with the reducibility of the respective support material, pointing to a distinct support effect and a direct participation of the support in the reaction. Activity measurements performed under ambient conditions show a similar trend of the activity as the TAP reactor measurements, supporting that the conclusions drawn from the TAP reactor measurements are valid also under continuous reaction conditions. Moreover, the rapid formation and accumulation of carbon-containing surface species during reaction is demonstrated, which can severely reduce the activity for CO oxidation. Implications of these results on the CO oxidation mechanism over metal oxide-supported catalysts are discussed. © 2010 Elsevier Inc. All rights reserved.
view abstract doi: 10.1016/j.jcat.2010.09.023 2010 • 5 Surface modification of polypropylene microfiltration membrane via entrapment of an amphiphilic alkyl oligoethyleneglycolether
Guo, H. and Ulbricht, M.
Journal of Membrane Science 349 312-320 (2010)For surface hydrophilic and antifouling modification of polypropylene (PP) microfiltration membrane, the novel method for entrapment of the amphiphilic modifier octaethyleneglycol monooctadecylether (C18E8) was investigated in detail. The effects of the modification conditions on PP membrane and polymer structure were characterized by gas flow/pore dewetting, nitrogen adsorption/BET analysis, scanning electron microscopy and X-ray diffraction; surface properties were evaluated by ATR-FTIR spectroscopy and static water contact angle; filtration performance as well as antifouling property were investigated by water flux measurement, trans-membrane zeta potential, static and dynamic protein adsorption experiments. Furthermore, a stability study of the modified membrane was performed to offer a comprehensive understanding of this physical entrapment strategy. It can be concluded that both outer surface and inner pore walls of PP membrane were covered with oligoethylene glycol after entrapment modification by C18E8, with only very slight changes of membrane pore and polymer structures. Correspondingly, PP membrane surface hydrophilicity and antifouling performance were evidently improved. It was also found that the entrapped modifier has a tendency to leach out of the PP membrane in water at room temperature. However, after 8 weeks changes became very small, and the modified PP membrane surface still exhibited significant hydrophilicity and antifouling properties. © 2009 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.memsci.2009.11.062 2010 • 4 The release of nickel from nickel-titanium (NiTi) is strongly reduced by a sub-micrometer thin layer of calcium phosphate deposited by rf-magnetron sputtering
Surmenev, R.A. and Ryabtseva, M.A. and Shesterikov, E.V. and Pichugin, V.F. and Peitsch, T. and Epple, M.
Journal of Materials Science: Materials in Medicine 21 1233-1239 (2010)Thin calcium phosphate coatings were deposited on NiTi substrates (plates) by rf-magnetron sputtering. The release of nickel upon immersion in water or in saline solution (0.9% NaCl in water) was measured by atomic absorption spectroscopy (AAS) for 42 days. The coating was analyzed before and after immersion by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). After an initial burst during the first 7 days that was observed for all samples, the rate of nickel release decreased 0.4-0.5 ng cm-2 d-1 for a 0.5 μm-thick calcium phosphate coating (deposited at 290 W). This was much less than the release from uncoated NiTi (3.4-4.4 ng cm-2 d-1). Notably, the nickel release rate was not significantly different in pure water and in aqueous saline solution. © 2010 Springer Science+Business Media, LLC.
view abstract doi: 10.1007/s10856-010-3989-5 2010 • 3 The use of calcium phosphate nanoparticles encapsulating Toll-like receptor ligands and the antigen hemagglutinin to induce dendritic cell maturation and T cell activation
Sokolova, V. and Knuschke, T. and Kovtun, A. and Buer, J. and Epple, M. and Westendorf, A.M.
Biomaterials 31 5627-5633 (2010)Dendritic cells (DCs) are potent antigen-presenting cells that possess the ability to stimulate naïve T cells. Antigen presentation by mature (activated) DCs is a prerequisite for the stimulation of antigen-specific T cells, whereas antigen presentation by immature DCs results in the generation of specific tolerance. Our aim was to develop calcium phosphate nanoparticles which can serve as carriers of immunoactive oligonucleotides into dendritic cells for their activation. We analyzed size, surface charge, and morphology of calcium phosphate nanoparticles loaded with the TLR ligands CpG and poly(I:C) and also with the antigen hemagglutinin (HA) by scanning electron microscopy, dynamic light scattering, Brownian motion analysis and ultracentrifugation. The uptake of fluorescence-labeled nanoparticles into dendritic cells was illustrated by confocal laser scanning microscopy. Immunostimulatory effects of these nanoparticles on DCs were studied, i.e., cytokine production and activation of the cells in terms of upregulation of surface molecules. We show that functionalized calcium phosphate nanoparticles are capable to induce both innate and adaptive immunity by activation of DCs. © 2010 Elsevier Ltd.
view abstract doi: 10.1016/j.biomaterials.2010.03.067 2010 • 2 Very low temperature CO oxidation over colloidally deposited gold nanoparticles on Mg(OH)2 and MgO
Jia, C.-N. and Liu, Y. and Bongard, H. and Schüth, F.
Journal of the American Chemical Society 132 1520-1522 (2010)(Figure Presented) The colloidal deposition method was used to prepare Au/Mg(OH)2 (0.7 wt % gold) catalysts with gold particle sizes between 1.5 to 5 nm which exhibited very high activity for CO oxidation with specific rates higher than 3.7 molCO·h-1·g Au-1 even at temperatures as low as -89° C. © 2010 American Chemical Society.
view abstract doi: 10.1021/ja909351e 2010 • 1 γ-Fe2O3 nanoparticle adsorption at an OTS Langmuir monolayer
Degen, P. and Paulus, M. and Leick, S. and Tolan, M. and Rehage, H.
Colloid and Polymer Science 288 643-651 (2010)The assembling of magnetic nanoparticles in ordered structures as well as the preparation of very thin magnetic switchable polymer membranes is an important aim in many technical fields. We studied the influence of γ-Fe2O3 nanoparticles on the polymerization process and on the properties of the poly(organosiloxane)/nanoparticle-composite layer by surface rheological measurements, surface pressure/area (π/A) isotherm measurements, and Brewster angle microscopy. The adsorption process dynamics were studied by X-ray reflectivity and surface potential measurements. The results confirm the presence of attractive electrostatic interactions between the partial negatively charged monolayer and the positively charged nanoparticles. For further investigations, we prepared Langmuir-Blodgett layers of these polymer-nanoparticle composite and investigated them by atomic force microscopy and UV-Vis spectroscopy. We found that the concentration of nanoparticles was very low and the particles were mainly arranged below the polymer layer. © 2010 Springer-Verlag.
view abstract doi: 10.1007/s00396-010-2191-0