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.
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2020 • 175 Study on machinability of additively manufactured and conventional titanium alloys in micro-milling process
Hojati, F. and Daneshi, A. and Soltani, B. and Azarhoushang, B. and Biermann, D.
Precision Engineering 62 1-9 (2020)Capability of Additive Manufacturing (AM) technology in the production of complex parts with high flexibility has led to the growing interest in their application as an alternative for conventional manufacturing processes. Despite the outstanding benefits of the AM process, due to their poor surface quality, the precision parts produced by this method generally need to be machined, ground, or polished. This paper addresses the machinability of AM Ti6Al4V titanium alloy parts in the micro-milling process with a specific focus on cutting forces, specific cutting energy, burr formation, and surface quality. Additive parts were produced by Electron Beam Melting (EBM) technique and were compared with the extruded Ti6Al4V parts in the micro-milling process. No significant difference could be observed in the cutting forces of both materials at chip thicknesses between 7.4 and 37.3 μm, despite the higher hardness of the EBM Ti6Al4V compared to the extruded Ti6Al4V. However, micro-milling of the EBM parts produced finer surfaces. Cutting forces and specific cutting energies of EBM parts were less than those of extruded parts at minimal chip thicknesses (lower than 7.4 μm). Continuous wavy-type burrs were formed in micro-milling of the EBM Ti6Al4V and were larger than those of extruded Ti6Al4V. © 2019 Elsevier Inc.
view abstract doi: 10.1016/j.precisioneng.2019.11.002 2020 • 174 Nanocast Mixed Ni-Co-Mn Oxides with Controlled Surface and Pore Structure for Electrochemical Oxygen Evolution Reaction
Priamushko, T. and Guillet-Nicolas, R. and Yu, M. and Doyle, M. and Weidenthaler, C. and Tuÿsüz, H. and Kleitz, F.
ACS Applied Energy Materials 3 5597-5609 (2020)Nanocasting or hard-templating is a versatile method to produce ordered mesoporous mixed transition metal oxides (MTMOs) with promising potential for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Herein, a comprehensive investigation was conducted on various NixCoyMnzO4 replicated from large pore KIT-6 silica. The materials were calcined at different temperatures to study the influence of the oxide formation and the resulting pore structure ordering, as well as surface properties, on the electrochemical activity and stability of the catalysts. After a comprehensive characterization, electrocatalytic performances of the materials were investigated in detail for OER to find a structure-activity relationship. In OER, a correlation was established between calcination temperature, pore and surface properties, and the overall efficiency and stability. The best sample, NixCoyMnzO4 calcined at 300 °C, provided a reasonable current density (25 mA/cm2 at 1.7 V vs RHE) and an overpotential of 400 mV at 10 mA/cm2, and demonstrated increased current density (above 200 mA/cm2 at 1.7 V vs RHE) once loaded into a Ni foam compared to the bare foam. This sample also remained stable over 15 h. Our results indicate that the calcination temperature greatly affects the porosity, crystalline structure, phase composition, and the activity of the catalysts toward OER. Copyright © 2020 American Chemical Society.
view abstract doi: 10.1021/acsaem.0c00544 2020 • 173 Performance of YSZ and Gd2Zr2O7/YSZ double layer thermal barrier coatings in burner rig tests
Vaßen, R. and Bakan, E. and Mack, D. and Schwartz-Lückge, S. and Sebold, D. and Jung Sohn, Y. and Zhou, D. and Guillon, O.
Journal of the European Ceramic Society 40 480-490 (2020)Double layer thermal barrier coatings (TBCs) consisting of a Gd2Zr2O7 (GZO) top and an ytrria stabilized zirconia (YSZ) interlayer have been tested in a burner rig facility and the results compared to the ones of conventional YSZ single layers. In order to gain insight in the high temperature capability of the alternative TBC material, high surface temperatures of up to 1550 °C have been chosen while keeping the bond coat temperature similar. It turned out that the performance of all systems is largely depending on the microstructure of the coatings especially reduced porosity levels of GZO being detrimental. In addition, it was more difficult in GZO than in YSZ coatings to obtain highly porous and still properly bonded microstructures. Another finding was the reduced lifetime with increasing surface temperatures, the amount of reduction is depending on the investigated system. The reasons for this behavior are analyzed and discussed in detail. © 2019 Elsevier Ltd
view abstract doi: 10.1016/j.jeurceramsoc.2019.10.021 2019 • 172 Piezoelectric 3-D Fibrous Poly(3-hydroxybutyrate)-Based Scaffolds Ultrasound-Mineralized with Calcium Carbonate for Bone Tissue Engineering: Inorganic Phase Formation, Osteoblast Cell Adhesion, and Proliferation
Chernozem, R.V. and Surmeneva, M.A. and Shkarina, S.N. and Loza, K. and Epple, M. and Ulbricht, M. and Cecilia, A. and Krause, B. and Baumbach, T. and Abalymov, A.A. and Parakhonskiy, B.V. and Skirtach, A.G. and Surmenev, R.A.
ACS Applied Materials and Interfaces (2019)Elaboration of novel biocomposites providing simultaneously both biodegradability and stimulated bone tissue repair is essential for regenerative medicine. In particular, piezoelectric biocomposites are attractive because of a possibility to electrically stimulate cell response. In the present study, novel CaCO3-mineralized piezoelectric biodegradable scaffolds based on two polymers, poly[(R)3-hydroxybutyrate] (PHB) and poly[3-hydroxybutyrate-co-3-hydroxyvalerate] (PHBV), are presented. Mineralization of the scaffold surface is carried out by the in situ synthesis of CaCO3 in the vaterite and calcite polymorphs using ultrasound (U/S). Comparative characterization of PHB and PHBV scaffolds demonstrated an impact of the porosity and surface charge on the mineralization in a dynamic mechanical system, as no essential distinction was observed in wettability, structure, and surface chemical compositions. A significantly higher (4.3 times) piezoelectric charge and a higher porosity (∼15%) lead to a more homogenous CaCO3 growth in 3-D fibrous structures and result in a two times higher relative mass increase for PHB scaffolds compared to that for PHBV. This also increases the local ion concentration incurred upon mineralization under U/S-generated dynamic mechanical conditions. The modification of the wettability for PHB and PHBV scaffolds from hydrophobic (nonmineralized fibers) to superhydrophilic (mineralized fibers) led to a pronounced apatite-forming behavior of scaffolds in a simulated body fluid. In turn, this results in the formation of a dense monolayer of well-distributed and proliferated osteoblast cells along the fibers. CaCO3-mineralized PHBV surfaces had a higher osteoblast cell adhesion and proliferation assigned to a higher amount of CaCO3 on the surface compared to that on PHB scaffolds, as incurred from micro-computed tomography (μCT). Importantly, a cell viability study confirmed biocompatibility of all the scaffolds. Thus, hybrid biocomposites based on the piezoelectric PHB polymers represent an effective scaffold platform functionalized by an inorganic phase and stimulating the growth of the bone tissue. © 2019 American Chemical Society.
view abstract doi: 10.1021/acsami.9b04936 2019 • 171 Adhesion, proliferation, and osteogenic differentiation of human mesenchymal stem cells on additively manufactured Ti6Al4V alloy scaffolds modified with calcium phosphate nanoparticles
Chudinova, E.A. and Surmeneva, M.A. and Timin, A.S. and Karpov, T.E. and Wittmar, A. and Ulbricht, M. and Ivanova, A. and Loza, K. and Prymak, O. and Koptyug, A. and Epple, M. and Surmenev, R.A.
Colloids and Surfaces B: Biointerfaces 176 130-139 (2019)In the present study, biocomposites based on 3D porous additively manufactured Ti6Al4V (Ti64) scaffolds modified with biocompatible calcium phosphate nanoparticles (CaPNPs) were investigated. Ti64 scaffolds were manufactured via electron beam melting technology using an Arcam machine. Electrophoretic deposition was used to modify the scaffolds with CaPNPs, which were synthesized by precipitation in the presence of polyethyleneimine (PEI). Dynamic light scattering revealed that the CaP/PEI nanoparticles had an average size of 46 ± 18 nm and a zeta potential of +22 ± 9 mV. Scanning electron microscopy (SEM) revealed that the obtained spherical CaPNPs had an average diameter of approximately 90 nm. The titanium-based scaffolds coated with CaPNPs exhibited improved hydrophilic surface properties, with a water contact angle below 5°. Cultivation of human mesenchymal stem cells (hMSCs) on the CaPNPs-coated Ti64 scaffolds indicated that the improved hydrophilicity was beneficial for the attachment and growth of cells in vitro. The Ti6Al4V/CaPNPs scaffold supported an increase in the alkaline phosphatase (ALP) activity of cells. In addition to the favourable cell proliferation and differentiation, Ti6Al4V/CaPNPs scaffolds displayed increased mineralization compared to non-coated Ti6Al4V scaffolds. Thus, the developed composite 3D scaffolds of Ti6Al4V functionalized with CaPNPs are promising materials for different applications related to bone repair. © 2018 Elsevier B.V.
view abstract doi: 10.1016/j.colsurfb.2018.12.047 2019 • 170 Examination of the Material Removal of unreinforced, thermoplastic Polymers by Scratch Tests
Kamplade, K. and Biermann, D.
Production Engineering 13 713-719 (2019)The use of plastics in the industry is steadily growing. Based on the material characteristics, such as low weight, conventional materials like steel are being replaced. For that reason, plastic components need to be machined to fulfill requirements regarding size shape and surface quality. Grinding processes are used to achieve high surface quality and dimensional and shape accuracy. The following article deals with scratch tests to basically analyse the grain engagement when grinding thermoplastics. For this, corundum grains are used in two different scratch test setups for fundamental analysis of the material removal process. The scratching process is evaluated by the relative chip volumes of the scratch grooves. In addition to that, the forces occuring during the process and the required specific scratch energy are analysed. © 2019, German Academic Society for Production Engineering (WGP).
view abstract doi: 10.1007/s11740-019-00925-z 2019 • 169 Investigation of virus retention by size exclusion membranes under different flow regimes
Kosiol, P. and Kahrs, C. and Thom, V. and Ulbricht, M. and Hansmann, B.
Biotechnology Progress 35 (2019)Virus removal by filter membranes is regarded as a robust and efficient unit operation, which is frequently applied in the downstream processing of biopharmaceuticals. The retention of viruses by virus filtration membranes is predominantly based on size exclusion. However, recent results using model membranes and bacteriophage PP7 point to the fact that virus retention can also significantly be influenced by adsorptive interactions between virus, product molecules, and membranes. Furthermore, the impact of flow rate and flow interruptions on virus retention have been studied and responsible mechanisms discussed. The aim of this investigation was to gain a holistic understanding of the underlying mechanisms for virus retention in size exclusion membranes as a function of membrane structure and membrane surface properties, as well as flow and solution conditions. The results of this study contribute to the differentiation between size exclusion and adsorptive effects during virus filtration and broaden the current understanding of mechanisms related to virus breakthroughs after temporary flow interruptions. Within the frame of a Design of Experiments approach it was found that the level of retention of virus filtration membranes was mostly influenced by the membrane structure during typical process-related flow conditions. The retention performance after a flow interruption was also significantly influenced by membrane surface properties and solution conditions. While size exclusion was confirmed as main retention mechanism, the analysis of all results suggests that especially after a flow interruption virus retention can be influenced by adsorptive effects between the virus and the membrane surface. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2747, 2019. © 2018 American Institute of Chemical Engineers
view abstract doi: 10.1002/btpr.2747 2019 • 168 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 • 167 Thermographic phosphor heat flux measurements of laminar methane/air flame impinging on a cylindrical surface
Oketch, P.O. and Gonchikzhapov, M. and Bergmann, U. and Atakan, B.
Measurement Science and Technology 30 (2019)The stagnation point heat fluxes of methane/air flames impinging normal on a cylindrical surface were determined experimentally. Light induced phosphorescence from thermographic phosphors was used to investigate surface temperatures at the stagnation point from a nearly 1D laminar premixed flame burning against a water-cooled ceramic tube. The ceramic tube was coated with 1.1% chromium-doped alumina (ruby) at the impingement area and excited with a green light-emitting diode (LED) to measure the surface temperature. The flame temperature profiles were also measured with a thermocouple of type R (Pt/Pt + 13% Rh). Effects on variations in cold gas velocity (0.1 m s-1-0.5 m s-1) relative to the flame speed, equivalence ratio (= 0.85-1.2), burner to impingement surface spacing (H/d = 0.5-2) and surface curvature are reported. The stagnation point heat fluxes are strongly influenced by the flame stabilization mechanism, which changes from burner to wall stabilization, which also is seen from the measured flame temperature profiles. Increasing the cold gas velocity of the reactants leads to higher stagnation point heat fluxes. In addition, decreasing the distance between the burner and impingement surface increases the heat flux, with higher heat fluxes recorded for a tube compared to a flat plate. © 2019 IOP Publishing Ltd.
view abstract doi: 10.1088/1361-6501/ab217e 2019 • 166 Al 2 O 3 /ZrO 2 -8Y 2 O 3 and (Cr,Ti)AlSiN tool coatings to influence the temperature and surface quality in friction-spinning processes
Tillmann, W. and Fehr, A. and Stangier, D. and Dildrop, M. and Homberg, W. and Lossen, B. and Hijazi, D.
Production Engineering 13 449-457 (2019)Friction-spinning is an incremental forming process, which is accompanied by complex thermal and mechanical loads in the tool and the formed part. To influence the process temperature, two main process parameters, i.e. the rotation speed and the feed rate, can be adapted. With the objective to improve the tool performance and the quality of the workpiece, this study focuses on a coating concept for friction-spinning tools made of high speed steel (HS6-5-2C, 1.3343). Atmospheric plasma sprayed (APS) Al 2 O 3 and ZrO 2 -8Y 2 O 3 coatings serve as a thermal insulator, while physically vapor deposited (PVD) Ti 16.7 Al 21.8 Si 7.9 N and Cr 18.7 Al 22.2 Si 7.5 N films are applied to increase the hardness of the tools. In addition, duplex coatings, combining the APS and PVD technique, are synthesized to influence both the heat transfer and the tribological properties of friction-spinning tools. Subsequently, all coated tools are tested in a friction-spinning process to form flanges made of AW-6060 (AlMgSi—3.3206) tube materials. The tool temperatures are determined in situ to investigate the impact of the tool coating on the process temperature. Compared to an uncoated tool, the alumina and zirconia coatings contribute to a reduction of the tool temperature by up to half, while the PVD films increase the hardness of the tool by 20 GPa. Furthermore, it is shown that the surface quality of thermally sprayed or PVD coated tools is directly related to the surface roughness of the resulting workpiece. © 2019, German Academic Society for Production Engineering (WGP).
view abstract doi: 10.1007/s11740-019-00899-y 2019 • 165 Effects of femtosecond laser shock peening in distilled water on the surface characterizations of NiTi shape memory alloy
Wang, H. and Pöhl, F. and Yan, K. and Decker, P. and Gurevich, E.L. and Ostendorf, A.
Applied Surface Science 471 869-877 (2019)NiTi shape memory alloy was processed by femtosecond laser shock peening (FLSP) without protective coating in distilled water to modify its surface characterizations. The surface topography, microhardness, microstructure and scratch testing were studied before and after FLSP treatment. The experimental results show that FLSP with different laser scanning speeds and passes can change the surface roughness and microhardness due to laser ablation and high pressure of shock wave. The average microhardness value of the specimens FLSPed in distilled water increased. Grain refinement was observed in the surface layer of FLSPed NiTi alloy. The scratch testing revealed that FLSP process can decrease the frictional force and coefficient of friction, and it also demonstrated that the FLSP technique is beneficial to enhance the surface wear property of NiTi alloy. © 2018 Elsevier B.V.
view abstract doi: 10.1016/j.apsusc.2018.12.087 2018 • 164 Influence of surface roughness on the shear strength of direct injection molded plastic-aluminum hybrid-parts
Bonpain, B. and Stommel, M.
International Journal of Adhesion and Adhesives 82 290-298 (2018)The strength of hybrid metal and plastic joints is strongly influenced by the surface roughness of metal. Although many investigations on the change in shear strength of adhesively bonded joints due to roughening have been published, it is not completely understood how different mean roughness indexes Ra of directly joined plastic-metal-parts correlate to the resulting shear strength. This paper describes a schematic roughness - shear strength curve for adhesively bonded specimens and an experimental one for direct injection molded hybrid specimens which is reconciled with the state of the art. Roughening the surface of the metal is realized by grit blasting using fused alumina. After that, the metal is coated by direct injection molded PA 6.6 with 30% short glass fiber and shear strength tests are carried out. It can be concluded that with increasing Ra the shear strength of adhesively bonded specimens increases to a first maximum, then decreases and finally increases again. Direct injection molded samples exhibit a similar trend. The difference is that the second increase is significantly more pronounced, leading to a second maximum which is nearly twice as high as the first one. This difference is explained by the lower strength of the adhesive compared to the plastic and the different pronounced so called surface area effects, notch effects and thickness effects. By increasing Ra they promote cohesive fracture which is detrimental for adhesively bonded but more beneficial for direct injection molded samples. To further explain the experimental results, a FEM model to predict the probability of failure, the expected stress and the failure mode for direct injection molded samples is developed. The FE-analyses confirm the explanatory approach on the joint strength in dependence of the Ra value. © 2018 Elsevier Ltd
view abstract doi: 10.1016/j.ijadhadh.2018.02.003 2018 • 163 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 2017 • 162 High-Throughput Structural and Functional Characterization of the Thin Film Materials System Ni-Co-Al
Decker, P. and Naujoks, D. and Langenkämper, D. and Somsen, C. and Ludwig, Al.
ACS Combinatorial Science 19 618-624 (2017)High-throughput methods were used to investigate a Ni-Co-Al thin film materials library, which is of interest for structural and functional applications (superalloys, shape memory alloys). X-ray diffraction (XRD) measurements were performed to identify the phase regions of the Ni-Co-Al system in its state after annealing at 600 °C. Optical, electrical, and magneto-optical measurements were performed to map functional properties and confirm XRD results. All results and literature data were used to propose a ternary thin film phase diagram of the Ni-Co-Al thin film system. © 2017 American Chemical Society.
view abstract doi: 10.1021/acscombsci.6b00176 2017 • 161 Compositional fingerprint of soy sauces via hydrophobic surface interaction
Jakobi, V. and Salmen, P. and Paulus, M. and Tolan, M. and Rosenhahn, A.
Food Chemistry 218 256-260 (2017)In this work, the interaction of soy sauces with hydrophobic surfaces has been analyzed. Hydrophobic self-assembled monolayers on gold or silicon dioxide were used to harvest conditioning layers from soy sauce products with varying amounts of additives. The data was compared to adsorption of soy protein and glutamic acid as common ingredients. Spectral ellipsometry revealed that all tested sauces led to the formation of thin overlayers on hydrophobic surfaces. Products with less additives yielded adlayers in the same thickness range as pure soy protein. In contrast, sauces with more ingredients create distinctly thicker films. Using water contact angle goniometry, it is shown that all adlayers render the substrate more hydrophilic. Infrared spectroscopy provided a deeper insight into the adlayer chemistry and revealed that the adlayer composition is dominated by protein rich components. X-ray reflectivity on selected films provided further insight into the density profiles within the adlayers on the molecular scale. © 2016 Elsevier Ltd
view abstract doi: 10.1016/j.foodchem.2016.09.045 2017 • 160 Antibacterial activity of microstructured sacrificial anode thin films by combination of silver with platinum group elements (platinum, palladium, iridium)
Köller, M. and Bellova, P. and Javid, S.M. and Motemani, Y. and Khare, C. and Sengstock, C. and Tschulik, K. and Schildhauer, T.A. and Ludwig, Al.
Materials Science and Engineering C 74 536-541 (2017)Five different Ag dots arrays (16 to 400dots/mm2) were fabricated on a continuous platinum, palladium, or iridium thin film and for comparison also on titanium film by sputter deposition and photolithographic patterning. To analyze the antibacterial activity of these microstructured films Staphylococcus aureus (S. aureus) were placed onto the array surfaces and cultivated overnight. To analyze the viability of planktonic as well as surface adherent bacteria, the applied bacterial fluid was subsequently aspirated, plated on blood agar plates and adherent bacteria were detected by fluorescence microscopy. A particular antibacterial effect towards . S. aureus was induced by Ag dot arrays on each of the platinum group thin film (sacrificial anode system for Ag) in contrast to Ag dot arrays fabricated on the Ti thin films (non-sacrificial anode system for Ag). Among platinum group elements the Ir-Ag system exerted the highest antibacterial activity which was accompanied by most advanced dissolution of the Ag dots and Ag ion release compared to Ag dots on Pt or Pd. © 2016 Elsevier B.V.
view abstract doi: 10.1016/j.msec.2016.12.075 2017 • 159 Optimizing inVitro Impedance and Physico-Chemical Properties of Neural Electrodes by Electrophoretic Deposition of Pt Nanoparticles
Koenen, S. and Rehbock, C. and Heissler, H.E. and Angelov, S.D. and Schwabe, K. and Krauss, J.K. and Barcikowski, S.
ChemPhysChem 18 1108-1117 (2017)Neural electrodes suffer from an undesired incline in impedance when in permanent contact with human tissue. Nanostructures, induced by electrophoretic deposition (EPD) of ligand-free laser-generated nanoparticles (NPs) on the electrodes are known to stabilize impedance invivo. Hence, Pt surfaces were systematically EPD-coated with Pt NPs and evaluated for impedance as well as surface coverage, contact angle, electrochemically active surface area (ECSA) and surface oxidation. The aim was to establish a systematic correlation between EPD process parameters and physical surface properties. The findings clearly reveal a linear decrease in impedance with increasing surface coverage, which goes along with a proportional reduction of the contact angle and an increase in ECSA and surface oxidation. EPD process parameters, prone to yield surface coatings with low impedance, are long deposition times (40-60min), while high colloid concentrations (>250μgmL-1) and electric field strengths (>25Vcm-1) should be avoided due to detrimental NP assemblage effects. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/cphc.201601180 2017 • 158 Optimizing in Vitro Impedance and Physico-Chemical Properties of Neural Electrodes by Electrophoretic Deposition of Pt Nanoparticles
Koenen, S. and Rehbock, C. and Heissler, H.E. and Angelov, S.D. and Schwabe, K. and Krauss, J.K. and Barcikowski, S.
ChemPhysChem 18 1108-1117 (2017)Neural electrodes suffer from an undesired incline in impedance when in permanent contact with human tissue. Nanostructures, induced by electrophoretic deposition (EPD) of ligand-free laser-generated nanoparticles (NPs) on the electrodes are known to stabilize impedance in vivo. Hence, Pt surfaces were systematically EPD-coated with Pt NPs and evaluated for impedance as well as surface coverage, contact angle, electrochemically active surface area (ECSA) and surface oxidation. The aim was to establish a systematic correlation between EPD process parameters and physical surface properties. The findings clearly reveal a linear decrease in impedance with increasing surface coverage, which goes along with a proportional reduction of the contact angle and an increase in ECSA and surface oxidation. EPD process parameters, prone to yield surface coatings with low impedance, are long deposition times (40–60 min), while high colloid concentrations (>250 μg mL−1) and electric field strengths (>25 V cm−1) should be avoided due to detrimental NP assemblage effects. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract doi: 10.1002/cphc.201601180 2017 • 157 Unusual application of aluminium-doped ZnO thin film developed by metalorganic chemical vapour deposition for surface temperature sensor
Nebatti, A. and Pflitsch, C. and Atakan, B.
Thin Solid Films 636 532-536 (2017)A relatively new promising method for surface temperature measurement is the use of thermographic phosphors. For this purpose, the temperature-dependent photoluminescence (PL) properties of aluminium-doped ZnO thin films were studied. The films have been successfully deposited on substrate of Si(100)-orientation by metalorganic chemical vapour deposition (MOCVD) method. For the use of the films as temperature sensors, the Photoluminescence (PL) properties are most important. Consequently, the emission peaks are observed in the undoped and Al-doped films deposited at 550 °C and annealed at 900 °C for 2 h after ultraviolet laser excitation (355 nm). The results show that with increasing temperature the PL intensity is quenched for the Al-doped ZnO film (n(Al)/n(Zn) = 0.051). As a result, the area under the spectrum changes significantly with temperature, making it useful for temperature evaluation. Al-doped ZnO films can be used as temperature sensors within the range of room temperature to 300 °C. Beyond this range the spectrum is no longer sensitive to temperature change.
view abstract doi: 10.1016/j.tsf.2017.07.002 2016 • 156 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 • 155 Mechanisms of femtosecond LIPSS formation induced by periodic surface temperature modulation
Applied Surface Science 374 56-60 (2016)Here we analyze the formation of laser-induced periodic surface structures (LIPSS) on metal surfaces upon single femtosecond laser pulses. Most of the existing models of the femtosecond LIPSS formation discuss only the appearance of a periodic modulation of the electron and ion temperatures. However the mechanism how the inhomogeneous surface temperature distribution induces the periodically-modulated surface profile under the conditions corresponding to ultrashort-pulse laser ablation is still not clear. Estimations made on the basis of different hydrodynamic instabilities allow to sort out mechanisms, which can bridge the gap between the temperature modulation and the LIPSS. The proposed theory shows that the periodic structures can be generated by single ultrashort laser pulses due to ablative instabilities. The Marangoni and Rayleigh-Bénard convection on the contrary cannot cause the LIPSS formation.
view abstract doi: 10.1016/j.apsusc.2015.09.091 2016 • 154 Osteogenic differentiation and proliferation of bone marrow-derived mesenchymal stromal cells on PDLLA + BMP-2-coated titanium alloy surfaces
Haversath, M. and Hülsen, T. and Böge, C. and Tassemeier, T. and Landgraeber, S. and Herten, M. and Warwas, S. and Krauspe, R. and Jäger, M.
Journal of Biomedical Materials Research - Part A 104 145-154 (2016)RhBMP-2 is clinically applied to enhance bone healing and used in combination with titanium fixation implants. The purpose of this in vitro study was to compare the osteogenic differentiation and proliferation of hMSC on native polished versus sandblasted titanium surfaces (TS) and to test their behavior on pure poly-D,L-lactide (PDLLA) coated as well as PDLLA + rhBMP-2 coated TS. Furthermore, the release kinetics of PDLLA + rhBMP-2-coated TS was investigated. Human bone marrow cells were obtained from three different donors (A: male, 16 yrs; B: male, 27 yrs, C: male, 49 yrs) followed by density gradient centrifugation and flow cytometry with defined antigens. The cells were seeded on native polished and sandblasted TS, PDLLA-coated TS and PDLLA + rhBMP-2-coated TS. Osteogenic differentiation (ALP specific activity via ALP and BCA assay) and proliferation (LDH cytotoxicity assay) was examined on day 7 and 14 and release kinetics of rhBMP-2 was investigated on day 3, 7, 10, and 14. We found significant higher ALP specific activity and LDH activity on native polished compared to native sandblasted surfaces. PDLLA led to decreased ALP specific and LDH activity on both surface finishes. Additional rhBMP-2 slightly diminished this effect. RhBMP-2-release from coated TS decreased nearly exponentially with highest concentrations at the beginning of the cultivation period. The results of this in vitro study suggest that native TS stimulate hMSC significantly stronger toward osteogenic differentiation and proliferation than rhBMP-2 + PDLLA-layered TS in the first 14 days of cultivation. The PDLLA-layer seems to inhibit local hMSC differentiation and proliferation. © 2015 Wiley Periodicals, Inc.
view abstract doi: 10.1002/jbm.a.35550 2016 • 153 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 • 152 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 • 151 Surface wettability and energy effects on the biological performance of poly-3-hydroxybutyrate films treated with RF plasma
Syromotina, D.S. and Surmenev, R.A. and Surmeneva, M.A. and Boyandin, A.N. and Nikolaeva, E.D. and Prymak, O. and Epple, M. and Ulbricht, M. and Oehr, C. and Volova, T.G.
Materials Science and Engineering C 62 450-457 (2016)The surface properties of poly-3-hydroxybutyrate (P3HB) membranes were modified using oxygen and an ammonia radio-frequency (RF, 13.56 MHz) plasma. The plasma treatment procedures used in the study only affected the surface properties, including surface topography, without inducing any significant changes in the crystalline structure of the polymer, with the exception being a power level of 250 W. The wettability of the modified P3HB surfaces was significantly increased after the plasma treatment, irrespective of the treatment procedure used. It was revealed that both surface chemistry and surface roughness changes caused by the plasma treatment affected surface wettability. A treatment-induced surface aging effect was observed and resulted in an increase in the water contact angle and a decrease in the surface free energy. However, the difference in the water contact angle between the polymers that had been treated for 4 weeks and the untreated polymer surfaces was still significant. A dependence between cell adhesion and proliferation and the polar component of the surface energy was revealed. The increase in the polar component after the ammonia plasma modification significantly increased cell adhesion and proliferation on biodegradable polymer surfaces compared to the untreated P3HB and the P3HB modified using an oxygen plasma. © 2016 Elsevier B.V.
view abstract doi: 10.1016/j.msec.2016.01.075 2016 • 150 Making the hydrogen evolution reaction in polymer electrolyte membrane electrolysers even faster
Tymoczko, J. and Calle-Vallejo, F. and Schuhmann, W. and Bandarenka, A.S.
Nature Communications 7 (2016)Although the hydrogen evolution reaction (HER) is one of the fastest electrocatalytic reactions, modern polymer electrolyte membrane (PEM) electrolysers require larger platinum loadings (∼0.5-1.0 mg cm-2) than those in PEM fuel cell anodes and cathodes altogether (∼0.5 mg cm-2). Thus, catalyst optimization would help in substantially reducing the costs for hydrogen production using this technology. Here we show that the activity of platinum(111) electrodes towards HER is significantly enhanced with just monolayer amounts of copper. Positioning copper atoms into the subsurface layer of platinum weakens the surface binding of adsorbed H-intermediates and provides a twofold activity increase, surpassing the highest specific HER activities reported for acidic media under similar conditions, to the best of our knowledge. These improvements are rationalized using a simple model based on structure-sensitive hydrogen adsorption at platinum and copper-modified platinum surfaces. This model also solves a long-lasting puzzle in electrocatalysis, namely why polycrystalline platinum electrodes are more active than platinum(111) for the HER.
view abstract doi: 10.1038/ncomms10990 2016 • 149 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 2015 • 148 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 • 147 Microfluidic detachment assay to probe the adhesion strength of diatoms
Alles, M. and Rosenhahn, A.
Biofouling 31 469-480 (2015)Fouling release (FR) coatings are increasingly applied as an environmentally benign alternative for controlling marine biofouling. As the technology relies on removing fouling by water currents created by the motion of ships, weakening of adhesion of adherent organisms is the key design goal for improved coatings. In this paper, a microfluidic shear force assay is used to quantify how easily diatoms can be removed from surfaces. The experimental setup and the optimization of the experimental parameters to study the adhesion of the diatom Navicula perminuta are described. As examples of how varying the physico-chemical surface properties affects the ability of diatoms to bind to surfaces, a range of hydrophilic and hydrophobic self-assembled monolayers was compared. While the number of cells that attached (adhered) was barely affected by the coatings, the critical shear stress required for their removal from the surface varied significantly. © 2015 Taylor & Francis.
view abstract doi: 10.1080/08927014.2015.1061655 2015 • 146 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 • 145 Wet-chemical synthesis of different bismuth telluride nanoparticles using metal organic precursors-single source vs. dual source approach
Bendt, G. and Weber, A. and Heimann, S. and Assenmacher, W. and Prymak, O. and Schulz, S.
Dalton Transactions 44 14272-14280 (2015)Thermolysis of the single source precursor (Et<inf>2</inf>Bi)<inf>2</inf>Te 1 in DIPB at 80 °C yielded phase-pure Bi<inf>4</inf>Te<inf>3</inf> nanoparticles, while mixtures of Bi<inf>4</inf>Te<inf>3</inf> and elemental Bi were formed at higher temperatures. In contrast, cubic Bi<inf>2</inf>Te particles were obtained by thermal decomposition of Et<inf>2</inf>BiTeEt 2 in DIPB. Moreover, a dual source approach (hot injection method) using the reaction of Te(SiEt<inf>3</inf>)<inf>2</inf> and Bi(NMe<inf>2</inf>)<inf>3</inf> was applied for the synthesis of different pure Bi-Te phases including Bi<inf>2</inf>Te, Bi<inf>4</inf>Te<inf>3</inf> and Bi<inf>2</inf>Te<inf>3</inf>, which were characterized by PXRD, REM, TEM and EDX. The influence of reaction temperature, precursor molar ratio and thermolysis conditions on the resulting material phase was verified. Moreover, reactions of alternate bismuth precursors such as Bi(NEt<inf>2</inf>)<inf>3</inf>, Bi(NMeEt)<inf>3</inf> and BiCl<inf>3</inf> with Te(SiEt<inf>3</inf>)<inf>2</inf> were investigated. © 2015 The Royal Society of Chemistry.
view abstract doi: 10.1039/c5dt02072g 2015 • 144 Shear-Induced Detachment of Polystyrene Beads from SAM-Coated Surfaces
Cho, K.L. and Rosenhahn, A. and Thelen, R. and Grunze, M. and Lobban, M. and Karahka, M.L. and Kreuzer, H.J.
Langmuir 31 11105-11112 (2015)In this work we experimentally and theoretically analyze the detachment of microscopic polystyrene beads from different self-assembled monolayer (SAM) surfaces in a shear flow in order to develop a mechanistic model for the removal of cells from surfaces. The detachment of the beads from the surface is treated as a thermally activated process applying an Arrhenius Ansatz to determine the activation barrier and attempt frequency of the rate determing step in bead removal. The statistical analysis of the experimental shear detachment data obtained in phosphate-buffered saline buffer results in an activation energy around 20 kJ/mol, which is orders of magnitude lower than the adhesion energy measured by atomic force microscopy (AFM). The same order of magnitude for the adhesion energy measured by AFM is derived from ab initio calculations of the van der Waals interaction energy between the polystyrene beads and the SAM-covered gold surface. We conclude that the rate determing step for detachment of the beads is the initiation of rolling on the surface (overcoming static friction) and not physical detachment, i.e., lifting the particle off the surface. © 2015 American Chemical Society.
view abstract doi: 10.1021/acs.langmuir.5b02321 2015 • 143 Ultra-Wideband Radar Diffraction Approximation for Dielectric Edges
Friederich, B. and Schultze, T. and Willms, I.
2015 IEEE International Conference on Ubiquitous Wireless Broadband, ICUWB 2015 (2015)In this paper, a diffraction simulation for dielectric edges is introduced. The simulation is based on geometrical theory of diffraction (GTD) and is implemented as an improvement of the millimeter-wave surface characterization. This material characterization technique has been introduced in  and uses the microwave ellipsometry. The subject of current investigations is the usage of autonomous security robots for the detection of hot spots, the localization and characterization of objects. These robots should support fire brigades or disaster relief teams by millimeter-wave surface characterization. The developed technique was inspired by the established optical ellipsometry. The optical characterization technique does not consider the effect diffraction at the edges of the surface. Hence, the ellipsometry is limited to large surfaces where the diffraction effects can be neglected, but for the supposed application it is necessary to compensate these effects. © 2015 IEEE.
view abstract doi: 10.1109/ICUWB.2015.7324523 2015 • 142 Salt induced reduction of lysozyme adsorption at charged interfaces
Göhring, H. and Paulus, M. and Salmen, P. and Wirkert, F. and Kruse, T. and Degen, P. and Stuhr, S. and Rehage, H. and Tolan, M.
Journal of Physics Condensed Matter 27 (2015)A study of lysozyme adsorption below a behenic acid membrane and at the solid-liquid interface between aqueous lysozyme solution and a silicon wafer in the presence of sodium chloride is presented. The salt concentration was varied between 1 mmol L-1 and 1000 mmol L-1. X-ray reflectivity data show a clear dependence of the protein adsorption on the salt concentration. Increasing salt concentrations result in a decreased protein adsorption at the interface until a complete suppression at high concentrations is reached. This effect can be attributed to a reduced attractive electrostatic interaction between the positively charged proteins and negatively charged surfaces by charge screening. The measurements at the solid-liquid interfaces show a transition from unoriented order of lysozyme in the adsorbed film to an oriented order with the short protein axis perpendicular to the solid-liquid interface with rising salt concentration. © 2015 IOP Publishing Ltd.
view abstract doi: 10.1088/0953-8984/27/23/235103 2015 • 141 Synthesis and post-synthetic modification of amine-, alkyne-, azide- and nitro-functionalized metal-organic frameworks based on DUT-5
Gotthardt, M.A. and Grosjean, S. and Brunner, T.S. and Kotzel, J. and Gänzler, A.M. and Wolf, S. and Bräse, S. and Kleist, W.
Dalton Transactions 44 16802-16809 (2015)Functionalized 4,4′-biphenyldicarboxylic acid molecules with additional amine, alkyne, azide or nitro groups were prepared and applied in the synthesis of novel metal-organic frameworks and mixed-linker metal-organic frameworks isoreticular to DUT-5. The properties of the frameworks could be tuned by varying the number of functional groups in the materials and the amine groups were employed in post-synthetic modification reactions without changing the framework structure or significantly decreasing the porosity of the materials. © The Royal Society of Chemistry 2015.
view abstract doi: 10.1039/c5dt02276b 2015 • 140 Correlation between surface properties and wettability of multi-scale structured biocompatible surfaces
Gorodzha, S.N. and Surmeneva, M.A. and Prymak, O. and Wittmar, A. and Ulbricht, M. and Epple, M. and Teresov, A. and Koval, N. and Surmenev, R.A.
IOP Conference Series: Materials Science and Engineering 98 (2015)The influence of surface properties of radio-frequency (RF) magnetron deposited hydroxyapatite (HA) and Si-containing HA coatings on wettability was studied. The composition and morphology of the coatings fabricated on titanium (Ti) were characterized using atomic force microscopy (AFM) and X-ray diffraction (XRD). The surface wettability was studied using contact angle analysis. Different geometric parameters of acid-etched (AE) and pulse electron beam (PEB)-treated Ti substrates and silicate content in the HA films resulted in the different morphology of the coatings at micro- and nano- length scales. Water contact angles for the HA coated Ti samples were evaluated as a combined effect of micro roughness of the substrate and nano-roughness of the HA films resulting in higher water contact angles compared with acid-etched (AE) or pulse electron beam (PEB) treated Ti substrates. © Published under licence by IOP Publishing Ltd.
view abstract doi: 10.1088/1757-899X/98/1/012026 2015 • 139 Potential-Assisted DNA Immobilization as a Prerequisite for Fast and Controlled Formation of DNA Monolayers
Jambrec, D. and Gebala, M. and La Mantia, F. and Schuhmann, W.
Angewandte Chemie - International Edition 54 15064-15068 (2015)Highly reproducible and fast potential-assisted immobilization of single-stranded (ss)DNA on gold surfaces is achieved by applying a pulse-type potential modulation. The desired DNA coverage can be obtained in a highly reproducible way within minutes. Understanding the underlying processes occurring during potential-assisted ssDNA immobilization is crucial. We propose a model that considers the role of ions surrounding the DNA strands, the distance dependence of the applied potentials within the electrolyte solution, and most importantly the shift of the potential of zero charge during the immobilization due to the surface modification with DNA. The control of the surface coverage of ssDNA as well as the achieved speed and high reproducibility are seen as prerequisites for improved DNA-based bioassays. Stir it up: The desired DNA coverage can be reached within minutes by stirring the DNA in front of an electrode by means of a pulse-type potential modulation. The mechanism of potential-assisted immobilization can be understood by considering the role of ions surrounding the DNA, the distance over which applied potentials have an impact on DNA, and the shift of the potential of zero charge (pzc) during the immobilization due to DNA immobilization. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/anie.201506672 2015 • 138 A novel approach for analyzing the dissolution mechanism of solid dispersions
Ji, Y. and Paus, R. and Prudic, A. and Lübbert, C. and Sadowski, G.
Pharmaceutical Research 32 2559-2578 (2015)Purpose To analyze the dissolution mechanism of solid dispersions of poorly water-soluble active pharmaceutical ingredients (APIs), to predict the dissolution profiles of the APIs and to find appropriate ways to improve their dissolution rate. Methods The dissolution profiles of indomethacin and naproxen from solid dispersions in PVP K25 were measured in vitro using a rotating-disk system (USP II). A chemical-potential-gradient model combined with the thermodynamic model PC-SAFT was developed to investigate the dissolution mechanism of indomethacin and naproxen from their solid dispersions at different conditions and to predict the dissolution profiles of these APIs. Results The results show that the dissolution of the investigated solid dispersions is controlled by dissolution of both, API and PVP K25 as they codissolve according to the initial API loading. Moreover, the dissolution of indomethacin and naproxen was improved by decreasing the API loading in polymer (leading to amorphous solid dispersions) and increasing stirring speed, temperature and pH of the dissolution medium. The dissolution of indomethacin and naproxen from their amorphous solid dispersions is mainly controlled by the surface reaction, which implies that indomethacin and naproxen dissolution can be effectively improved by formulation design and by improving their solvation performance. Conclusions The chemical-potential-gradient model combined with PC-SAFTcan be used to analyze the dissolution mechanism of solid dispersions and to describe and predict the dissolution profiles of API as function of stirring speed, temperature and pH value of the medium. This work helps to find appropriate ways to improve the dissolution rate of poorly-soluble APIs. © Springer Science+Business Media New York 2015.
view abstract doi: 10.1007/s11095-015-1644-z 2015 • 137 Phase transitions during formation of Ag nanoparticles on In 2S 3precursor layers
Liu, Y. and Fu, Y. and Dittrich, T. and Sáez-Araoz, R. and Schmid, M. and Hinrichs, V. and Lux-Steiner, M.C. and Fischer, C.-H.
Thin Solid Films 590 54-59 (2015)Phase transitions have been investigated for silver deposition onto In<inf>2</inf>S<inf>3</inf> precursor layers by spray chemical vapor deposition from a trimethylphosphine (hexafluoroacetylacetonato) silver (Ag(hfacac)(PMe<inf>3</inf>)) solution. The formation of Ag nanoparticles (Ag NPs) on top of the semiconductor layer set on concomitant with the formation of AgIn<inf>5</inf>S<inf>8</inf>. The increase of the diameter of Ag NPs was accompanied by the evolution of orthorhombic AgInS<inf>2</inf>. The formation of Ag<inf>2</inf>S at the interface between Ag NPs and the semiconductor layer was observed. Surface photovoltage spectroscopy indicated charge separation and electronic transitions in the ranges of corresponding band gaps. The phase transition approach is aimed to be applied for the formation of plasmonic nanostructures on top of extremely thin semiconducting layers. © 2015 Elsevier B.V.
view abstract doi: 10.1016/j.tsf.2015.07.021 2015 • 136 Site-Directed, On-Surface Assembly of DNA Nanostructures
Meyer, R. and Saccà, B. and Niemeyer, C.M.
Angewandte Chemie - International Edition 54 12039-12043 (2015)Two-dimensional DNA lattices have been assembled from DNA double-crossover (DX) motifs on DNA-encoded surfaces in a site-specific manner. The lattices contained two types of single-stranded protruding arms pointing into opposite directions of the plane. One type of these protruding arms served to anchor the DNA lattice on the solid support through specific hybridization with surface-bound, complementary capture oligomers. The other type of arms allowed for further attachment of DNA-tethered probe molecules on the opposite side of the lattices exposed to the solution. Site-specific lattice assembly and attachment of fluorophore-labeled oligonucleotides and DNA-protein conjugates was demonstrated using DNA microarrays on flat, transparent mica substrates. Owing to their programmable orientation and addressability over a broad dynamic range from the nanometer to the millimeter length scale, such supramolecular architecture might be used for presenting biomolecules on surfaces, for instance, in biosensor applications. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/anie.201505553 2015 • 135 Surface properties of annealed semiconducting β-Ga 2O 3(1 0 0) single crystals for epitaxy
Navarro-Quezada, A. and Galazka, Z. and Alamé, S. and Skuridina, D. and Vogt, P. and Esser, N.
Applied Surface Science 349 368-373 (2015)We present a detailed study on the surface properties of conductive β-Ga<inf>2</inf>O<inf>3</inf> (1 0 0) single-crystal epiready substrates by means of photoelectron emission spectroscopy. The surface properties are studied prior and after annealing in ultra-high vacuum (UHV). We find that untreated substrates contain a significant amount of adsorbed carbon contaminations at the surface, which can be partly removed by annealing at 800 °C in UHV. Valence band photoemission evidences an upward band bending of about 0.5 eV that increases with annealing, revealing the presence of an electron depletion layer at the near-surface region responsible for the insulating behavior commonly observed for semiconductive β-Ga<inf>2</inf>O<inf>3</inf> single crystals. Our findings become crucial for epitaxial growth, as it is known that carbon modifies the electrical and structural properties of subsequent epitaxial layers. © 2015 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.apsusc.2015.04.225 2015 • 134 Effects of various chair-side surface treatment methods on dental restorative materials with respect to contact angles and surface roughness
Sturz, C.R.C. and Faber, F.-J. and Scheer, M. and Rothamel, D. and Neugebauer, J.
Dental Materials Journal 34 796-813 (2015)Available chair-side surface treatment methods may adversely affect prosthetic materials and promote plaque accumulation. This study investigated the effects of treatment procedures on three resin restorative materials, zirconium-dioxide and polyetheretherketone in terms of surface roughness and hydrophobicity. Treatments were grinding with silicon carbide paper or white Arkansas stone, blasting with prophylaxis powder and polishing with diamond paste. Surface roughness was assessed using confocal laser scanning. Hydrophobicity as measured by water contact angle was determined by computerized image analysis using the sessile drop technique. All of the specific surface treatments performed led to significant changes in contact angle values and surface roughness (Ra) values. Median contact angle values ranged from 51.6° to 114°. Ra values ranged from 0.008 μm to 2.917 μm. Air-polishing as well as other polishing procedures increased surface roughness values in all materials except zirconium dioxide. Polyetheretherketone displayed greatest change in contact angle values after air-polishing treatment. © 2015, Japanese Society for Dental Materials and Devices. All rights reserved.
view abstract doi: 10.4012/dmj.2014-098 2015 • 133 Nano-hydroxyapatite-coated metal-ceramic composite of iron-tricalcium phosphate: Improving the surface wettability, adhesion and proliferation of mesenchymal stem cells in vitro
Surmeneva, M.A. and Kleinhans, C. and Vacun, G. and Kluger, P.J. and Schönhaar, V. and Müller, M. and Hein, S.B. and Wittmar, A. and Ulbricht, M. and Prymak, O. and Oehr, C. and Surmenev, R.A.
Colloids and Surfaces B: Biointerfaces 135 386-393 (2015)Thin radio-frequency magnetron sputter deposited nano-hydroxyapatite (HA) films were prepared on the surface of a Fe-tricalcium phosphate (Fe-TCP) bioceramic composite, which was obtained using a conventional powder injection moulding technique. The obtained nano-hydroxyapatite coated Fe-TCP biocomposites (nano-HA-Fe-TCP) were studied with respect to their chemical and phase composition, surface morphology, water contact angle, surface free energy and hysteresis. The deposition process resulted in a homogeneous, single-phase HA coating. The ability of the surface to support adhesion and the proliferation of human mesenchymal stem cells (hMSCs) was studied using biological short-term tests in vitro. The surface of the uncoated Fe-TCP bioceramic composite showed an initial cell attachment after 24 h of seeding, but adhesion, proliferation and growth did not persist during 14 days of culture. However, the HA-Fe-TCP surfaces allowed cell adhesion, and proliferation during 14 days. The deposition of the nano-HA films on the Fe-TCP surface resulted in higher surface energy, improved hydrophilicity and biocompatibility compared with the surface of the uncoated Fe-TCP. Furthermore, it is suggested that an increase in the polar component of the surface energy was responsible for the enhanced cell adhesion and proliferation in the case of the nano-HA-Fe-TCP biocomposites. © 2015 Elsevier B.V.
view abstract doi: 10.1016/j.colsurfb.2015.07.057 2015 • 132 Doping Level of Boron-Doped Diamond Electrodes Controls the Grafting Density of Functional Groups for DNA Assays
Švorc, L. and Jambrec, D. and Vojs, M. and Barwe, S. and Clausmeyer, J. and Michniak, P. and Marton, M. and Schuhmann, W.
ACS Applied Materials and Interfaces 7 18949-18956 (2015)The impact of different doping levels of boron-doped diamond on the surface functionalization was investigated by means of electrochemical reduction of aryldiazonium salts. The grafting efficiency of 4-nitrophenyl groups increased with the boron levels (B/C ratio from 0 to 20 000 ppm). Controlled grafting of nitrophenyldiazonium was used to adjust the amount of immobilized single-stranded DNA strands at the surface and further on the hybridization yield in dependence on the boron doping level. The grafted nitro functions were electrochemically reduced to the amine moieties. Subsequent functionalization with a succinic acid introduced carboxyl groups for subsequent binding of an amino-terminated DNA probe. DNA hybridization significantly depends on the probe density which is in turn dependent on the boron doping level. The proposed approach opens new insights for the design and control of doped diamond surface functionalization for the construction of DNA hybridization assays. © 2015 American Chemical Society.
view abstract doi: 10.1021/acsami.5b06394 2015 • 131 A novel approach for the characterization of liquid phase adsorption on activated carbons
Treese, J. and Pasel, C. and Luckas, M. and Bathen, D.
Chemie-Ingenieur-Technik 87 563-570 (2015)Abstract Activated carbons are widely applicable in industrial adsorption processes. However, characterization of their surface properties is problematic due to the number of different source materials and variations in production processes. Here, a model of the carbon surface derived that is based on the knowledge of fundamental molecular interactions on carbon surfaces. Adsorption isotherms of selected probe molecules are measured on different activated carbons and discussed how the model can be applied in the characterization of the surface properties of activated carbons. Copyright © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/cite.201400085 2015 • 130 Holographic microscopy provides new insights into the settlement of zoospores of the green alga Ulva linza on cationic oligopeptide surfaces
Vater, S.M. and Finlay, J. and Callow, M.E. and Callow, J.A. and Ederth, T. and Liedberg, B. and Grunze, M. and Rosenhahn, A.
Biofouling 31 229-239 (2015)Interaction of zoospores of Ulva linza with cationic, arginine-rich oligopeptide self-assembled monolayers (SAMs) is characterized by rapid settlement. Some spores settle (ie permanently attach) in a ‘normal’ manner involving the secretion of a permanent adhesive, retraction of the flagella and cell wall formation, whilst others undergo ‘pseudosettlement’ whereby motile spores are trapped (attached) on the SAM surface without undergoing the normal metamorphosis into a settled spore. Holographic microscopy was used to record videos of swimming zoospores in the vicinity of surfaces with different cationic oligopeptide concentrations to provide time-resolved insights into processes associated with attachment of spores. The data reveal that spore attachment rate increases with increasing cationic peptide content. Accordingly, the decrease in swimming activity in the volume of seawater above the surface accelerated with increasing surface charge. Three-dimensional trajectories of individual swimming spores showed a ‘hit and stick’ motion pattern, exclusively observed for the arginine-rich peptide SAMs, whereby spores were immediately trapped upon contact with the surface. © 2015 Taylor & Francis.
view abstract doi: 10.1080/08927014.2015.1022534 2015 • 129 Effect of the addition of low rare earth elements (lanthanum, neodymium, cerium) on the biodegradation and biocompatibility of magnesium
Willbold, E. and Gu, X. and Albert, D. and Kalla, K. and Bobe, K. and Brauneis, M. and Janning, C. and Nellesen, J. and Czayka, W. and Tillmann, W. and Zheng, Y. and Witte, F.
Acta Biomaterialia 11 554-562 (2015)Rare earth elements are promising alloying element candidates for magnesium alloys used as biodegradable devices in biomedical applications. Rare earth elements have significant effects on the high temperature strength as well as the creep resistance of alloys and they improve magnesium corrosion resistance. We focused on lanthanum, neodymium and cerium to produce magnesium alloys with commonly used rare earth element concentrations. We showed that low concentrations of rare earth elements do not promote bone growth inside a 750 μm broad area around the implant. However, increased bone growth was observed at a greater distance from the degrading alloys. Clinically and histologically, the alloys and their corrosion products caused no systematic or local cytotoxicological effects. Using microtomography and in vitro experiments, we could show that the magnesium-rare earth element alloys showed low corrosion rates, both in in vitro and in vivo. The lanthanum- and cerium-containing alloys degraded at comparable rates, whereas the neodymium-containing alloy showed the lowest corrosion rates. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
view abstract doi: 10.1016/j.actbio.2014.09.041 2014 • 128 Influence of zwitterionic SAMs on protein adsorption and the attachment of algal cells
Bauer, S. and Alles, M. and Finlay, J.A. and Callow, J.A. and Callow, M.E. and Rosenhahn, A.
Journal of Biomaterials Science, Polymer Edition 25 1530-1539 (2014)Zwitterionic polymers are non-fouling materials with immense potential for a range of biological applications. Here, we describe the resistance of zwitterionic self-assembled monolayers prepared from different solution ratios of positively and negatively charged thiols towards the adhesion of proteins, zoospores of the green alga Ulva linza, and cells of the unicellular alga Navicula perminuta. While mixed zwitterionic surfaces with a high hydrophilic nature significantly reduced the adhesion strength of the two algae, the positively and negatively charged components were far less effective. © 2014 Taylor and Francis.
view abstract doi: 10.1080/09205063.2014.929429 2014 • 127 Experimental investigation of the pullout behavior of steel fibers in high-strength concrete
Breitenbücher, R. and Song, F.
Beton- und Stahlbetonbau 109 43-52 (2014)Steel-fiber-reinforced concretes are used more and more also in structural concrete elements. Examples for these are among others tunnel lining segments. In this case there is a specific characteristic, that concretes for such elements usually have a compressive strength between 70 and 90 N/mm2. These concretes are very brittle with only low fracture toughness, so that damages in form of cracking and spalling often occur in the periphery of the segments. By the addition of steel fibers the ductility of the concrete can be considerably improved. The primary question is, to which extend the stresses can be transferred in concrete cracks by the fibers bridging these cracks. To investigate the bonding behavior between steel fiber and concrete matrix, single fiber pullout tests were performed in high-strength concrete matrix. Various parameters such as fiber shape, geometry, tensile strength, surface properties, inclination angle and embedment length were investigated. Based on the experimental results, the effect of those parameters on pullout force versus slip relationship, pullout work, fiber utilization and fiber/matrix failure mode were analyzed and discussed. Copyright © 2014 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin.
view abstract doi: 10.1002/best.201300049 2014 • 126 Structural complexity in metal-organic frameworks: Simultaneous modification of open metal sites and hierarchical porosity by systematic doping with defective linkers
Fang, Z. and Dürholt, J.P. and Kauer, M. and Zhang, W. and Lochenie, C. and Jee, B. and Albada, B. and Metzler-Nolte, N. and Pöppl, A. and Weber, B. and Muhler, M. and Wang, Y. and Schmid, R. and Fischer, R.A.
Journal of the American Chemical Society 136 9627-9636 (2014)A series of defect-engineered metal-organic frameworks (DEMOFs) derived from parent microporous MOFs was obtained by systematic doping with defective linkers during synthesis, leading to the simultaneous and controllable modification of coordinatively unsaturated metal sites (CUS) and introduction of functionalized mesopores. These materials were investigated via temperature-dependent adsorption/desorption of CO monitored by FTIR spectroscopy under ultra-high-vacuum conditions. Accurate structural models for the generated point defects at CUS were deduced by matching experimental data with theoretical simulation. The results reveal multivariate diversity of electronic and steric properties at CUS, demonstrating the MOF defect structure modulation at two length scales in a single step to overcome restricted active site specificity and confined coordination space at CUS. Moreover, the DEMOFs exhibit promising modified physical properties, including band gap, magnetism, and porosity, with hierarchical micro/mesopore structures correlated with the nature and the degree of defective linker incorporation into the framework. © 2014 American Chemical Society.
view abstract doi: 10.1021/ja503218j 2014 • 125 Thermal loads of working coils in electromagnetic sheet metal forming
Gies, S. and Löbbe, C. and Weddeling, C. and Tekkaya, A.E.
Journal of Materials Processing Technology 214 2537-2544 (2014)One basic problem of electromagnetic forming is the limited tool life. Besides the mechanical loads especially thermal loads acting on the tool coil affect its lifetime. In electromagnetic forming, about 50% of the deployed electrical energy is lost because of joule heating in the working coil. In case of high volume production, an accumulation of this heat promotes failure of the coil and reduces the coil lifetime. Despite this importance of the thermal loads only insufficient information about the coil temperature and its influencing parameters is available. Focus of this paper is on the determination of the temperature distribution in case of long-term discharge sequences. Experimental investigations using an infrared camera were performed to measure the coil surface temperature. Numerical process simulation is used to gather information about the temperature inside the working coil. The results prove that the coil reaches an equilibrium temperature after several discharges. For the analyzed range of input power the maximum coil surface temperature and the maximum coil winding temperature reached values of 92 °C and 178 °C, respectively. These temperatures exceed the weakening temperature of most reinforcement and insulation materials. The derived knowledge about the parameters influencing the coil temperature can be used for an improved process design to avoid thermal overstressing of the coil. A comparison of experiments with and without workpiece deformation revealed that the temperature in case of prevented deformation is always higher, and thus, represents an upper bound for the coil temperature. © 2014 Elsevier B.V.
view abstract doi: 10.1016/j.jmatprotec.2014.05.005 2014 • 124 Hydrogels from phospholipid vesicles
Gräbner, D. and Hoffmann, H. and Förster, S. and Rosenfeldt, S. and Linders, J. and Mayer, C. and Talmon, Y. and Schmidt, J.
Advances in Colloid and Interface Science 208 252-263 (2014)It is shown that phospholipid dispersions with a few percent of diacylphosphocholine PC in water can be swollen to single-phase lyotropic liquid crystalline Lα-phases by the addition of co-solvents like glycerol, 1,3-butyleneglycol BG or 1,2-propyleneglycol PG. The birefringent Lα-phases contain small unilamellar and multilamellar vesicles if the temperature of the samples is above the Krafft-Temperature Tm of the phospholipid. When such transparent birefringent viscous samples are cooled down below Tm the samples are transformed into birefringent gels. Cryo-TEM and FF-TEM measurements show that the bilayers of the vesicles are transformed from the liquid to the crystalline state during the transformation while the vesicle structure remains. The bilayers of the crystalline vesicles form adhesive contacts in the gel. Pulsed-field gradient NMR measurements show that two different kinds of water or co-solvent can be distinguished in the gels. One type of solvent molecules can diffuse like normal solvent in a continuous bulk phase. A second type of water diffuses much more slowly. This type of solvent is obviously trapped in the vesicles. The permeability of the crystalline vesicles for water and solvent molecules is much lower in the crystalline state than in the fluid state. Maximum swelling of the diacylphosphocholin dispersions occurs when the refractive index of the solvent is matched to the refractive index of the bilayers. The attraction between the bilayers is at a minimum in this state and the liquid crystalline L α-phase's undulation forces between the bilayers push the bilayers apart. On transformation to the gel state the crystalline bilayers assume a high elastic bending rigidity. Undulations of the bilayers are now suppressed, and the bilayers can form adhesive contacts. Oscillating rheological measurements show that the gels with only 1% of phospholipids can have a storage modulus of 1000 Pa. The gels are very brittle. They break when they are deformed by a few percent. © 2014 Elsevier B.V.
view abstract doi: 10.1016/j.cis.2014.02.011 2014 • 123 Computation of dispersion curves for embedded waveguides using a dashpot boundary condition
Gravenkamp, H. and Birk, C. and Song, C.
Journal of the Acoustical Society of America 135 1127-1138 (2014)In this paper a numerical approach is presented to compute dispersion curves for solid waveguides coupled to an infinite medium. The derivation is based on the scaled boundary finite element method that has been developed previously for waveguides with stress-free surfaces. The effect of the surrounding medium is accounted for by introducing a dashpot boundary condition at the interface between the waveguide and the adjoining medium. The damping coefficients are derived from the acoustic impedances of the surrounding medium. Results are validated using an improved implementation of an absorbing region. Since no discretization of the surrounding medium is required for the dashpot approach, the required number of degrees of freedom is typically 10 to 50 times smaller compared to the absorbing region. When compared to other finite element based results presented in the literature, the number of degrees of freedom can be reduced by as much as a factor of 4000. © 2014 Acoustical Society of America.
view abstract doi: 10.1121/1.4864303 2014 • 122 Differences between healthy hematopoietic progenitors and leukemia cells with respect to CD44 mediated rolling versus adherence behavior on hyaluronic acid coated surfaces
Hanke, M. and Hoffmann, I. and Christophis, C. and Schubert, M. and Hoang, V.T. and Zepeda-Moreno, A. and Baran, N. and Eckstein, V. and Wuchter, P. and Rosenhahn, A. and Ho, A.D.
Biomaterials 35 1411-1419 (2014)We previously demonstrated that leukemia cell lines expressing CD44 and hematopoietic progenitor cells (HPC) from umbilical cord blood (CB) showed rolling on hyaluronic acid (HA)-coated surfaces under physiological shear stress. In the present study, we quantitatively assessed the interaction of HPC derived from CB, mobilized peripheral blood (mPB) and bone marrow (BM) from healthy donors, as well as primary leukemia blasts from PB and BM of patients with acute myeloid leukemia (AML) with HA. We have demonstrated that HPC derived from healthy donors showed relative homogeneous rolling and adhesion to HA. In contrast, highly diverse behavioral patterns were found for leukemia blasts under identical conditions. The monoclonal CD44 antibody (clone BU52) abrogated the shear stress-induced rolling of HPC and leukemia blasts, confirming the significance of CD44 in this context. On the other hand, the immobile adhesion of leukemia blasts to the HA-coated surface was, in some cases, not or incompletely inhibited by BU52. The latter property was associated with non-responsiveness to induction chemotherapy and subsequently poor clinical outcome. © 2013 Elsevier Ltd.
view abstract doi: 10.1016/j.biomaterials.2013.11.011 2014 • 121 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 • 120 The development of chiral nematic mesoporous materials
Kelly, J.A. and Giese, M. and Shopsowitz, K.E. and Hamad, W.Y. and MacLachlan, M.J.
Accounts of Chemical Research 47 1088-1096 (2014)ConspectusCellulose nanocrystals (CNCs) are obtained from the sulfuric acid-catalyzed hydrolysis of bulk cellulose. The nanocrystals have diameters of ∼5-15 nm and lengths of ∼100-300 nm (depending on the cellulose source and hydrolysis conditions). This lightweight material has mostly been investigated to reinforce composites and polymers because it has remarkable strength that rivals carbon nanotubes. But CNCs have an additional, less explored property: they organize into a chiral nematic (historically referred to as cholesteric) liquid crystal in water. When dried into a thin solid film, the CNCs retain the helicoidal chiral nematic order and assemble into a layered structure where the CNCs have aligned orientation within each layer, and their orientation rotates through the stack with a characteristic pitch (repeating distance). The cholesteric ordering can act as a 1-D photonic structure, selectively reflecting circularly polarized light that has a wavelength nearly matching the pitch.During CNC self-assembly, it is possible to add sol-gel precursors, such as Si(OMe)4, that undergo hydrolysis and condensation as the solvent evaporates, leading to a chiral nematic silica/CNC composite material. Calcination of the material in air destroys the cellulose template, leaving a high surface area mesoporous silica film that has pore diameters of ∼3-10 nm. Importantly, the silica is brilliantly iridescent because the pores in its interior replicate the chiral nematic structure. These films may be useful as optical filters, reflectors, and membranes.In this Account, we describe our recent research into mesoporous films with chiral nematic order. Taking advantage of the chiral nematic order and nanoscale of the CNC templates, new functional materials can be prepared. For example, heating the silica/CNC composites under an inert atmosphere followed by removal of the silica leaves highly ordered, mesoporous carbon films that can be used as supercapacitor electrodes. The composition of the mesoporous films can be varied by using assorted organosilica precursors. After removal of the cellulose by acid-catalyzed hydrolysis, highly porous, iridescent organosilica films are obtained. These materials are flexible and offer the ability to tune the chemical and mechanical properties through variation of the organic spacer.Chiral nematic mesoporous silica and organosilica materials, obtainable as centimeter-scale freestanding films, are interesting hosts for nanomaterials. When noble metal nanoparticles are incorporated into the pores, they show strong circular dichroism signals associated with their surface plasmon resonances that arise from dipolar coupling of the particles within the chiral nematic host. Fluorescent conjugated polymers show induced circular dichroism spectra when encapsulated in the chiral nematic host. The porosity, film structure, and optical properties of these materials could enable their use in sensors.We describe the development of chiral nematic mesoporous silica and organosilica, demonstrate different avenues of host-guest chemistry, and identify future directions that exploit the unique combination of properties present in these materials. The examples covered in this Account demonstrate that there is a rich diversity of composite materials accessible using CNC templating. © 2014 American Chemical Society.
view abstract doi: 10.1021/ar400243m 2014 • 119 Improving the cutting conditions in the five-axis micromilling of hardened high-speed steel by applying a suitable tool inclination
Krebs, E. and Kersting, P.
Procedia CIRP 14 366-370 (2014)In case of manufacturing miniaturized products with 3D features, micromachining is a suitable technology. By using a five-axis process, it is possible to produce complex products with high material removal rates. Further benefits are, for example, higher tool stiffness due to the possibility of utilizing tools with shorter cantilever lengths and higher surface qualities, which can be achieved by avoiding cutting with the center of the tool when using ball-end milling cutters. A tool inclination can not only be used to avoid the center cut in the five-axis process, but also to achieve better cutting conditions. In this paper, the influence of the tool inclination is analyzed for micromilling hardened high-speed steel (S6-5-2, 63 HRC). The presented results show the possibility of reducing tool wear and achieving better surface qualities by applying a specific tool inclination. This knowledge can be used to generate optimized NC programs for the five-axis micromilling of hardened steels. © 2014 Published by Elsevier B.V.
view abstract doi: 10.1016/j.procir.2014.03.032 2014 • 118 Hybrid processes in manufacturing
Lauwers, B. and Klocke, F. and Klink, A. and Tekkaya, A.E. and Neugebauer, R. and McIntosh, D.
CIRP Annals - Manufacturing Technology 63 561-583 (2014)Hybrid manufacturing processes are based on the simultaneous and controlled interaction of process mechanisms and/or energy sources/tools having a significant effect on the process performance. These processes have a large influence on the processing/manufacturing characteristics resulting in higher machinability, reductions of process forces and tool wear, etc. Due to the combined action of processes, it also has an important - and most of the time - positive effect on the surface integrity of machined parts. This paper gives a definition and classification of hybrid processes, followed by a description of principles and future perspectives, benefits on productivity, effects on surface quality and applications of common hybrid processes. © 2014 CIRP.
view abstract doi: 10.1016/j.cirp.2014.05.003 2014 • 117 Barnacle cyprid motility and distribution in the water column as an indicator of the settlement-inhibiting potential of nontoxic antifouling chemistries
Maleschlijski, S. and Bauer, S. and Di Fino, A. and Sendra, G.H. and Clare, A.S. and Rosenhahn, A.
Biofouling 30 1055-1065 (2014)Testing of new coatings to control fouling frequently involves single-species laboratory bioassays. Barnacle cyprids are among the most widely used model organisms in marine biofouling research, and surfaces that inhibit their settlement are considered to be promising candidates for new coating concepts. An analysis of motility parameters (mean velocity and swimming area coefficient) and distribution of cyprids of Balanus amphitrite in different swimming regions in the vicinity of model surfaces (self-assembled monolayers) is presented. The data are correlated with the settlement preferences of cyprids on these surfaces. Cyprids were predominantly found in interfacial regions and the transition frequencies between swimming regions of different depths were determined. © 2014, © 2014 Taylor & Francis.
view abstract doi: 10.1080/08927014.2014.966097 2014 • 116 Characterisation of non-uniform functional surfaces: Towards linking basic surface properties with electrocatalytic activity
Maljusch, A. and Henry, J.B. and Tymoczko, J. and Bandarenka, A.S. and Schuhmann, W.
RSC Advances 4 1532-1537 (2014)Functional materials, particularly heterogeneous catalysts, are often non-uniform at a microscopic level making their detailed characterisation extremely complex. This complexity inhibits the design and implementation of novel functional materials as such characterisation is a key to understanding interfaces for heterogeneous catalysis. We demonstrate that a combination of Scanning Kelvin Probe (SKP) and Scanning Electrochemical Microscopy (SECM) experiments made over the same sample surface using an integrated SKP-SECM system provides a powerful and robust tool to link basic surface properties with the observed electrocatalytic activity. As the SKP-response can be accurately assessed using modern quantum chemical approaches to benchmark analytical signals for different surface structures with varying compositions, application of an integrated SKP-SECM system can offer valuable insight into the origin of the observed electrocatalytic activity. As model objects, we used Pt(111)-like thin films modified with sub-monolayer and monolayer amounts of Cu atoms located at the electrode surface and in the sub-surface region. The exact position of the Cu atoms relative to the topmost Pt layer greatly affects basic surface properties and governs the electrocatalytic activity of the surface towards various reactions, i.e. the oxygen reduction reaction. SKP-SECM appeared to be a very sensitive tool to monitor those changes as a function of the spatial coordinates. © 2014 The Royal Society of Chemistry.
view abstract doi: 10.1039/c3ra45845h 2014 • 115 Effects of bleaching agents on surface roughness of filling materials
Markovic, L. and Jordan, R.A. and Glasser, M.-C. and Arnold, W.H. and Nebel, J. and Tillmann, W. and Ostermann, T. and Zimmer, S.
Dental Materials Journal 33 59-63 (2014)The aim of this study was to use a non-tactile optical measurement system to assess the effects of three bleaching agents' concentrations on the surface roughness of dental restoration materials. Two composites (Grandio, Venus) and one glass ionomer cement (Ketac Fil Plus) were used in this in vitro study. Specimens were treated with three different bleaching agents (16% and 22% carbamide peroxide (Polanight) and 38% hydrogen peroxide (Opalescence Boost)). Surface roughness was measured with an optical profilometer (Infinite Focus G3) before and after the bleaching treatment. Surface roughness increased in all tested specimens after bleaching treatment (p<0.05). Our in vitro study showed that dental bleaching agents influenced the surface roughness of different restoration materials, and the restoration material itself was shown to have an impact on alteration susceptibility. There seemed to be no clinical relevance in case of an optimal finish.
view abstract doi: 10.4012/dmj.2012-217 2014 • 114 Tribolayer formation in a metal-on-metal (MoM) hip joint: An electrochemical investigation
Mathew, M.T. and Nagelli, C. and Pourzal, R. and Fischer, A. and Laurent, M.P. and Jacobs, J.J. and Wimmer, M.A.
Journal of the Mechanical Behavior of Biomedical Materials 29 199-212 (2014)The demand for total hip replacement (THR) surgery is increasing in the younger population due to faster rehabilitation and more complete restoration of function. Up to 2009, metal-on-metal (MoM) hip joint bearings were a popular choice due to their design flexibility, post-operative stability and relatively low wear rates. The main wear mechanisms that occur along the bearing surface of MoM joints are tribochemical reactions that deposit a mixture of wear debris, metal ions and organic matrix of decomposed proteins known as a tribolayer. No in-depth electrochemical studies have been reported on the structure and characteristics of this tribolayer or about the parameters involved in its formation.In this study, we conducted an electrochemical investigation of different surfaces (bulk-like: control, nano-crystalline: new implant and tribolayer surface: retrieved implant) made out of two commonly used hip CoCrMo alloys (high-carbon and low-carbon). As per ASTM standard, cyclic polarization tests and electrochemical impedance spectroscopy tests were conducted. The results obtained from electrochemical parameters for different surfaces clearly indicated a reduction in corrosion for the tribolayer surface (Icorr: 0.76μA/cm2). Further, polarization resistance (Rp:2.39±0.60MΩ/cm2) and capacitance (Cdl:15.20±0.75μF/cm2) indicated variation in corrosion kinetics for the tribolayer surface, that attributed to its structure and stability in a simulated body environment. © 2013 Elsevier Ltd.
view abstract doi: 10.1016/j.jmbbm.2013.08.018 2014 • 113 Interaction of colloidal nanoparticles with their local environment: The (ionic) nanoenvironment around nanoparticles is different from bulk and determines the physico-chemical properties of the nanoparticles
Pfeiffer, C. and Rehbock, C. and Hühn, D. and Carrillo-Carrion, C. and De Aberasturi, D.J. and Merk, V. and Barcikowski, S. and Parak, W.J.
Journal of the Royal Society Interface 11 (2014)The physico-chemical properties of colloidal nanoparticles (NPs) are influenced by their local environment, as, in turn, the local environment influences the physico-chemical properties of the NPs. In other words, the local environment around NPs has a profound impact on the NPs, and it is different from bulk due to interaction with the NP surface. So far, this important effect has not been addressed in a comprehensive way in the literature. The vicinity of NPs can be sensitively influenced by local ions and ligands, with effects already occurring at extremely low concentrations. NPs in the Hückel regime are more sensitive to fluctuations in the ionic environment, because of a larger Debye length. The local ion concentration hereby affects the colloidal stability of the NPs, as it is different from bulk owing to Debye Hückel screening caused by the charge of the NPs. This can have subtle effects, now caused by the environment to the performance of the NP, such as for example a buffering effect caused by surface reaction on ultrapure ligandfree nanogold, a size quenching effect in the presence of specific ions and a significant impact on fluorophore-labelled NPs acting as ion sensors. Thus, the aim of this review is to clarify and give an unifying view of the complex interplay between the NP's surface with their nanoenvironment. © 2014 The Author(s) Published by the Royal Society. All rights reserved.
view abstract doi: 10.1098/rsif.2013.0931 2014 • 112 Design of a tribocorrosion bioreactor for the analysis of immune cell response to in situ generated wear products
Pourzal, R. and Cichon, R. and Mathew, M.T. and Pacione, C.A. and Fischer, A. and Hallab, N. and Wimmer, M.A.
Journal of Long-Term Effects of Medical Implants 24 65-76 (2014)Adverse local tissue reactions to wear debris and corrosion products have lead to a sharp decline in the use of metal-on-metal (MOM) total hip athroplasties (THAs) clinically. Today, approximately 1 million patients are still carrying such a device. To gain a better understanding of the effect of wear and corrosion products on cells within the joint environment, it is important to generate conditions in vitro that resemble the in vivo system as closely as possible. In this paper, we present a novel tribocorrosion bioreactor that enables the simultaneous conduction of tribocorrosion and cell-culture experiments. In this setup, macrophage cell cultures are located in direct proximity to a tribological interface mimicking the sliding conditions of THA and are exposed to wear and corrosion products as they are generated. These products may include meta-stable species and metallo-organic complexes that have not been considered in earlier studies. The combination of standard tribological, electrochemical, and biological techniques is associated with several challenges that are described here in detail. © 2014 by Begell House, Inc.
view abstract doi: 10.1615/JLongTermEffMedImplants.2014010305 2014 • 111 Photothermal laser fabrication of micro- and nanostructured chemical templates for directed protein immobilization
Schröter, A. and Franzka, S. and Hartmann, N.
Langmuir 30 14841-14848 (2014)Photothermal patterning of poly(ethylene glycol) terminated organic monolayers on surface-oxidized silicon substrates is carried out using a microfocused beam of a CW laser operated at a wavelength of 532 nm. Trichlorosilane and trimethoxysilane precursors are used for coating. Monolayers from trimethoxysilane precursors show negligible unspecific protein adsorption in the background, i.e., provide platforms of superior protein repellency. Laser patterning results in decomposition of the monolayers and yields chemical templates for directed immobilization of proteins at predefined positions. Characterization is carried out via complementary analytical methods including fluorescence microscopy, atomic force microscopy, and scanning electron microscopy. Appropriate labeling techniques (fluorescent markers and gold clusters) and substrates (native and thermally oxidized silicon substrates) are chosen in order to facilitate identification of protein adsorption and ensure high sensitivity and selectivity. Variation of the laser parameters at a 1/e2 spot diameter of 2.8 μm allows for fabrication of protein binding domains with diameters on the micrometer and nanometer length scale. Minimum domain sizes are about 300 nm. In addition to unspecific protein adsorption on as-patterned monolayers, biotin-streptavidin coupling chemistry is exploited for specific protein binding. This approach represents a novel facile laser-based means for fabrication of protein micro- and nanopatterns. The routine is readily applicable to femtosecond laser processing of glass substrates for the fabrication of transparent templates. (Graph Presented). © 2014 American Chemical Society.
view abstract doi: 10.1021/la503814n 2014 • 110 One-step synthesis of bismuth molybdate catalysts via flame spray pyrolysis for the selective oxidation of propylene to acrolein
Schuh, K. and Kleist, W. and Høj, M. and Trouillet, V. and Jensen, A.D. and Grunwaldt, J.-D.
Chemical Communications 50 15404-15406 (2014)Flame spray pyrolysis (FSP) of Bi(iii)- and Mo(vi)-2-ethylhexanoate dissolved in xylene resulted in various nanocrystalline bismuth molybdate phases depending on the Bi/Mo ratio. Besides α-Bi2Mo3O12 and γ-Bi2MoO6, FSP gave direct access to the metastable β-Bi2Mo2O9 phase with high surface area (19 m2 g-1). This phase is normally only obtained at high calcination temperatures (>560 °C) resulting in lower surface areas. The β-phase was stable up to 400 °C and showed superior catalytic performance compared to α- and γ-phases in selective oxidation of propylene to acrolein at temperatures relevant for industrial applications (360 °C). This journal is © The Royal Society of Chemistry.
view abstract doi: 10.1039/c4cc07527g 2014 • 109 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 • 108 Conditioning of self-assembled monolayers at two static immersion test sites along the east coast of Florida and its effect on early fouling development
Thome, I. and Bauer, S. and Vater, S. and Zargiel, K. and Finlay, J.A. and Arpa-Sancet, M.P. and Alles, M. and Callow, J.A. and Callow, M.E. and Swain, G.W. and Grunze, M. and Rosenhahn, A.
Biofouling 30 1011-1021 (2014)Among the first events after immersion of surfaces in the ocean is surface ‘conditioning’. Here, the accumulation and composition of the conditioning films formed after immersion in the ocean are analyzed. In order to account for different surface chemistries, five self-assembled monolayers that differ in resistance to microfouling and wettability were used. Water samples from two static immersion test sites along the east coast of Florida were collected at two different times of the year and used for experiments. Spectral ellipsometry revealed that conditioning films were formed within the first 24 h and contact angle goniometry showed that these films changed the wettability and rendered hydrophobic surfaces more hydrophilic and vice versa. Infrared reflection adsorption spectroscopy showed that the composition of the conditioning film depended on both the wettability and immersion site. Laboratory and field assays showed that the presence of a conditioning film did not markedly influence settlement of microorganisms. © 2014, © 2014 Taylor & Francis.
view abstract doi: 10.1080/08927014.2014.957195 2014 • 107 Electrical potential-assisted DNA hybridization. How to mitigate electrostatics for surface DNA hybridization
Tymoczko, J. and Schuhmann, W. and Gebala, M.
ACS Applied Materials and Interfaces 6 21851-21858 (2014)Surface-confined DNA hybridization reactions are sensitive to the number and identity of DNA capture probes and experimental conditions such as the nature and the ionic strength of the electrolyte solution. When the surface probe density is high or the concentration of bulk ions is much lower than the concentration of ions within the DNA layer, hybridization is significantly slowed down or does not proceed at all. However, high-density DNA monolayers are attractive for designing high-sensitivity DNA sensors. Thus, circumventing sluggish DNA hybridization on such interfaces allows a high surface concentration of target DNA and improved signal/noise ratio. We present potential-assisted hybridization as a strategy in which an external voltage is applied to the ssDNA-modified interface during the hybridization process. Results show that a significant enhancement of hybridization can be achieved using this approach. © 2014 American Chemical Society.
view abstract doi: 10.1021/am5027902 2014 • 106 X-ray reflectivity measurements of liquid/solid interfaces under high hydrostatic pressure conditions
Wirkert, F.J. and Paulus, M. and Nase, J. and Möller, J. and Kujawski, S. and Sternemann, C. and Tolan, M.
Journal of Synchrotron Radiation 21 76-81 (2014)A high-pressure cell for in situ X-ray reflectivity measurements of liquid/solid interfaces at hydrostatic pressures up to 500 MPa (5 kbar), a pressure regime that is particularly important for the study of protein unfolding, is presented. The original set-up of this hydrostatic high-pressure cell is discussed and its unique properties are demonstrated by the investigation of pressure-induced adsorption of the protein lysozyme onto hydrophobic silicon wafers. The presented results emphasize the enormous potential of X-ray reflectivity studies under high hydrostatic pressure conditions for the in situ investigation of adsorption phenomena in biological systems.© 2014 International Union of Crystallography.
view abstract doi: 10.1107/S1600577513021516 2013 • 105 Thermographic phosphor thermometry in transient combustion: A theoretical study of heat transfer and accuracy
Atakan, B. and Roskosch, D.
Proceedings of the Combustion Institute 34 3603-3610 (2013)Thermographic phosphors (TPs) are used in combustion environments to study wall surface temperatures and heat fluxes. Recently they are also applied in unsteady environments like internal combustion engines to study the heat transfer to walls. The present study investigates theoretically some related effects leading to limitations of the method and thus trying to help experimenters to choose proper conditions for their experiments. The influence of absorptivity and film thickness is studied first. Then the unsteady heat flux of a surrounding gas phase is investigated as a function of film thickness and conductivity, including the effect on the temperatures which would be measured using TPs. The errors in temperature measurements and time resolution are investigated for typical cases. Finally the relation between the surface temperature and film thickness is investigated for combinations of two base materials (quartz and steel) coated with layers of Mg2SiO4 or SiO2, as representatives for TP host materials. It is seen that the maximum surface temperature is influenced in unsteady heat transfer processes even by relatively thin layers. © 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
view abstract doi: 10.1016/j.proci.2012.05.022 2013 • 104 Adhesion of marine fouling organisms on hydrophilic and amphiphilic polysaccharides
Bauer, S. and Arpa-Sancet, M.P. and Finlay, J.A. and Callow, M.E. and Callow, J.A. and Rosenhahn, A.
Langmuir 29 4039-4047 (2013)Polysaccharides are a promising material for nonfouling surfaces because their chemical composition makes them highly hydrophilic and able to form water-storing hydrogels. Here we investigated the nonfouling properties of hyaluronic acid (HA) and chondroitin sulfate (CS) against marine fouling organisms. Additionally, the free carboxyl groups of HA and CS were postmodified with the hydrophobic trifluoroethylamine (TFEA) to block free carboxyl groups and render the surfaces amphiphilic. All coatings were tested with respect to their protein resistance and against settlement and adhesion of different marine fouling species. Both the settlement and adhesion strength of a marine bacterium (Cobetia marina), zoospores of the seaweed Ulva linza, and cells of a diatom (Navicula incerta) were reduced compared to glass control surfaces. In most cases, TFEA capping increased or maintained the performance of the HA coatings, whereas for the very well performing CS coatings the antifouling performance was reduced after capping. © 2013 American Chemical Society.
view abstract doi: 10.1021/la3038022 2013 • 103 Investigation of different hard coatings for micromilling of austenitic stainless steel
Biermann, D. and Steiner, M. and Krebs, E.
Procedia CIRP 7 246-251 (2013)(Micro-)Machining of austenitic stainless steel is highly challenging due to the formation of build-up edges, adhesive tool wear and also the ability for work hardening, the low thermal conductivity, and the high toughness. Here, the application of tool coatings is a suitable method to extend tool life and to improve consequently the overall workpiece quality. Yet the qualification of different tool coatings for micromilling austenitic stainless steel has to be analysed. In this investigation micromilling experiments applying two fluted endmills having a diameter of d = 1 mm with different hard coatings were applied. The austenitic stainless steel X5CrNi18-10 (1.4301) served as the workpiece material. The tool coatings were CrN, TiN, AlCrN, AlTiN and TiAlN. Using a constant set of cutting parameters and the same basic tool geometry, the achievable performance of the different coatings was evaluated in terms of the process forces, the tool wear and the achievable surface quality. The application of a TiAlN and AlCrN coating generated very good results regarding the tool wear. Relating to the surface quality, the AlTiN coating provided the best results. © 2013 The Authors.
view abstract doi: 10.1016/j.procir.2013.05.042 2013 • 102 On surface temperature measurements with thermographic phosphors: A review
Brübach, J. and Pflitsch, C. and Dreizler, A. and Atakan, B.
Progress in Energy and Combustion Science 39 37-60 (2013)Surface temperatures, which are important in many combustion and energy transfer processes, can be measured optically using rare-earth or transition metal doped ceramic materials, so-called thermographic phosphors. For this purpose, the surface is coated with a thin phosphor film, which can be excited by different light sources. The properties of the subsequently emitted luminescence are exploited for temperature determination employing appropriate calibration measurements. The present review introduces the basic principles with regards to combustion and energy science. In this context, a broad overview of phosphor film preparation techniques is presented. For the first time, an entire error analysis is given for this technique, which may sensitise future studies for error sources and encourage an estimation of their total accuracy. Finally, a tabulated survey provides a broad database, which may help future work to identify appropriate phosphor materials. © 2012 Elsevier Ltd. All rights reserved.
view abstract doi: 10.1016/j.pecs.2012.06.001 2013 • 101 Failure mechanisms of magnesia alumina spinel abradable coatings under thermal cyclic loading
Ebert, S. and Mücke, R. and Mack, D. and Vaßen, R. and Stöver, D. and Wobst, T. and Gebhard, S.
Journal of the European Ceramic Society 33 3335-3343 (2013)Abradable coatings have been used in low- and high-pressure sections of jet engine compressors for more than 40 years. Today, they are also used in the high-pressure turbine of jet engines and are gaining more interest for applications in industrial gas turbines. They minimise the clearance between the rotating blade tips and the stationary liners. Aside from being abradable, the coatings have to be mechanically stable and withstand high thermo-mechanical loadings. A typical material used in engines today is yttria-stabilised zirconia (YSZ). This material advantageously combines a suitable thermal conductivity with a high thermal expansion coefficient, but shows a temperature capability limited to 1200 °C in long-term applications. Typical abradable coating thicknesses are above 1. mm. With increasing coating thickness and limited cooling efficiency leading to high surface temperatures, there is a risk of premature failure. As a result, new ceramic materials have been developed with better high-temperature capability. The present work investigates an atmospheric plasma sprayed ceramic double-layer coating system composed of 7YSZ as an intermediate layer and magnesia alumina spinel as a top layer. This double-layer system was sprayed onto disc-shaped Inconel 738 superalloy substrates, which were coated with a vacuum plasma sprayed MCrAlY bondcoat. The lifetime of the coating system was assessed via thermal gradient cycling testing with surface temperatures above 1400 °C. During cycling, the samples showed a typical failure mechanism with exfoliation of thin coating lamellae starting from the coating surface. This failure mechanism was not observed in thermal barrier or abradable coatings in the past. The failure mechanism was analysed and mismatch stress calculations were carried out. © 2013 Elsevier Ltd.
view abstract doi: 10.1016/j.jeurceramsoc.2013.06.021 2013 • 100 Interfacial roughening in nonideal fluids: Dynamic scaling in the weak- and strong-damping regime
Gross, M. and Varnik, F.
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 87 (2013)Interfacial roughening denotes the nonequilibrium process by which an initially flat interface reaches its equilibrium state, characterized by the presence of thermally excited capillary waves. Roughening of fluid interfaces has been first analyzed by Flekkoy and Rothman, where the dynamic scaling exponents in the weakly damped case in two dimensions were found to agree with the Kardar-Parisi-Zhang universality class. We extend this work by taking into account also the strong-damping regime and perform extensive fluctuating hydrodynamics simulations in two dimensions using the Lattice Boltzmann method. We show that the dynamic scaling behavior is different in the weakly and strongly damped case. © 2013 American Physical Society.
view abstract doi: 10.1103/PhysRevE.87.022407 2013 • 99 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 • 98 Osteoblastic potency of bone marrow cells cultivated on functionalized biometals with cyclic RGD-peptide
Jäger, M. and Böge, C. and Janissen, R. and Rohrbeck, D. and Hülsen, T. and Lensing-Höhn, S. and Krauspe, R. and Herten, M.
Journal of Biomedical Materials Research - Part A 101 2905-2914 (2013)The fixation of cementless endoprostheses requires excellent fixation at the bone implant interface. Although the surface structures of these implants are designed to promote osteoblastic differentiation, poor bone quality may prevent or delay osseointegration. There is evidence that RGD peptides known as recognition motifs for various integrins, promote cellular adhesion, influence cellular proliferation, and differentiation of local cells. In this study, five different metal surfaces were analyzed: Sandblasted (TiSa) and polished (TiPol) Ti6Al4V, porocoated (CCPor) and polished (CCPol) cobalt chrome and polished stainless steel (SS) were coated by ethanol amine and poly(ethylene glycol) to attach covalently RGD peptides. Human mesenchymal stromal cells of healthy donors were cultivated onto prior functionalized metal surfaces for 14 days without osteogenic stimulation. Cell proliferation and differentiation were quantitatively evaluated for native (I), NaOH pre-activated (II), NaOH pre-activated, and PEG-coated (III) as well as for RGD (IV) coated surfaces. The RGD immobilization efficiency was analyzed by epi-fluorescence spectroscopy, cell morphology was documented by light and scanning electron microscopy. The RGD-binding efficiency was TiSa > TiPol > SS > CCPor > CCPol. RGD coated surfaces showed the highest average cell proliferation on CCPol > SS > CCPor > TiSa ≥ TiPol, whereas cellular differentiation mostly correlated with the observed proliferation results, such as CCPol > TiSa > SS > CCPor > TiPol. Considering statistical analyses (significance level of α = 0.05), the RGD-coating of all biometals in comparison and in respect of their particular controls showed no significant improvement in cellular proliferation and osteoblastic differentiation. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 101A: 2905-2914, 2013. Copyright © 2013 Wiley Periodicals, Inc., a Wiley Company.
view abstract doi: 10.1002/jbm.a.34590 2013 • 97 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 • 96 Fundamentals for controlling thickness and surface quality during dieless necking-in of tubes by spinning
Kwiatkowski, L. and Tekkaya, A.E. and Kleiner, M.
CIRP Annals - Manufacturing Technology 62 299-302 (2013)Dieless necking-in by spinning is a highly flexible process to manufacture tubular parts with variable cross-sections and nearly arbitrary contours. However, the thickness distribution of such products is influenced primarily by the toolpath. Based on analytical models this study introduces the fundamentals to control the tube thickness. Two principal tool movements are identified causing different deformation modes: shear-necking, which leads to thickening, and stretch-necking, which leads to thinning. Based on an additional model for the surface quality general criteria are derived to setup basic process parameters. The developed approach is validated by various experiments. © 2013 CIRP.
view abstract doi: 10.1016/j.cirp.2013.03.054 2013 • 95 Surface grafting of Corchorus olitorius fibre: A green approach for the development of activated bioadsorbent
Roy, A. and Chakraborty, S. and Kundu, S.P. and Majumder, S.B. and Adhikari, B.
Carbohydrate Polymers 92 2118-2127 (2013)The present work is an endeavor to prepare lignocellulosic biomass based adsorbent, suitable for removal of organic and inorganic pollutants from industrial effluents. Lignocellulosic Corchorus olitorius fibre (jute fibre) surface was grafted with naturally available polyphenol, tannin, preceded by the epoxy-activation of fibre surface with epichlorohydrin under mild condition in an aqueous suspension. The reaction parameters for the modification, viz., concentration of epichlorohydrin and tannin, time, and temperature were optimized. The successful occurrence of surface modification of jute fibre (JF) was characterized and estimated from weight gain percent, elemental analysis, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, scanning electron and atomic force microscopy, and thermogravimetric analysis. An extensive analysis of deconvoluted FTIR spectra using the Voigt model was utilized to ensure the surface grafting. The microbiological susceptibility study revealed high persistency of JF towards biodegradation after efficient grafting with tannin. © 2012 Elsevier Ltd.
view abstract doi: 10.1016/j.carbpol.2012.11.039 2013 • 94 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 • 93 Rapid immuno-SERS microscopy for tissue imaging with single-nanoparticle sensitivity
Salehi, M. and Steinigeweg, D. and Ströbel, P. and Marx, A. and Packeisen, J. and Schlücker, S.
Journal of Biophotonics 6 785-792 (2013)Immuno-SERS microscopy is a novel imaging technique in nano-biophotonics, which employs antibodies labeled with SERS-active nanoparticles in conjunction with Raman microscopy. Rapid data acquisition is of central importance for screening large areas of tissue specimens. Here, we first discuss the role of SERS labels with single-particle sensitivity in immuno-SERS microscopy, in particular with respect to false-negative results. In combined single-particle experiments (SERS microscopy/dark-field microscopy/HR-SEM), we then demonstrate that small glass-coated clusters (dimers and trimers) of gold nanospheres exhibit the desired single-particle SERS sensitivity, even at acquisition times as short as 30 msec per pixel, while monomers do not. The proof-of-concept for rapid immuno-SERS microscopy with 30 msec acquisition time per pixel for selective imaging of the p53 family member p63 in prostate tissue sections is demonstrated. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/jbio.201200148 2013 • 92 Surface anchored metal-organic frameworks as stimulus responsive antifouling coatings
Sancet, M.P.A. and Hanke, M. and Wang, Z. and Bauer, S. and Azucena, C. and Arslan, H.K. and Heinle, M. and Gliemann, H. and Wöll, C. and Rosenhahn, A.
Biointerphases 8 (2013)Surface-anchored, crystalline and oriented metal organic frameworks (SURMOFs) have huge potential for biological applications due to their well-defined and highly-porous structure. In this work we describe a MOF-based, fully autonomous system, which combines sensing, a specific response, and the release of an antimicrobial agent. The Cu-containing SURMOF, Cu-SURMOF 2, is stable in artificial seawater and shows stimulus-responsive anti-fouling properties against marine bacteria. When Cobetia marina adheres on the SURMOF, the framework's response is lethal to the adhering microorganism. A thorough analysis reveals that this response is induced by agents secreted from the microbes after adhesion to the substrate, and includes a release of Cu ions resulting from a degradation of the SURMOF. The stimulus-responsive antifouling effect of Cu-SURMOF 2 demonstrates the first application of Cu-SURMOF 2 as autonomous system with great potential for further microbiological and cell culture applications. © 2013 Arpa Sancet et al.
view abstract doi: 10.1186/1559-4106-8-29 2013 • 91 Universal method for protein immobilization on chemically functionalized germanium investigated by ATR-FTIR difference spectroscopy
Schartner, J. and Güldenhaupt, J. and Mei, B. and Rögner, M. and Muhler, M. and Gerwert, K. and Kötting, C.
Journal of the American Chemical Society 135 4079-4087 (2013)Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy allows a detailed analysis of surface attached molecules, including their secondary structure, orientation, and interaction with small molecules in the case of proteins. Here, we present a universal immobilization technique on germanium for all oligo-histidine-tagged proteins. For this purpose, new triethoxysilane derivates were developed: we synthesized a linker-silane with a succinimidyl ester as amine-reactive headgroup and a matrix-silane with an unreactive ethylene glycol group. A new methodology for the attachment of triethoxysilanes on germanium was established, and the surface was characterized by ATR-FTIR and X-ray photoelectron spectroscopy. In the next step, the succinimidyl ester was reacted with aminonitrilotriacetic acid. Subsequently, Ni2+ was coordinated to form Ni-nitrilotriacetic acid for His-tag binding. The capability of the functionalized surface was demonstrated by experiments using the small GTPase Ras and photosystem I (PS I). The native binding of the proteins was proven by difference spectroscopy, which probes protein function. The function of Ras as molecular switch was demonstrated by a beryllium trifluoride anion titration assay, which allows observation of the "on" and "off" switching of Ras at atomic resolution. Furthermore, the activity of immobilized PS I was proven by light-induced difference spectroscopy. Subsequent treatment with imidazole removes attached proteins, enabling repeated binding. This universal technique allows specific attachment of His-tagged proteins and a detailed study of their function at the atomic level using FTIR difference spectroscopy. © 2013 American Chemical Society.
view abstract doi: 10.1021/ja400253p 2013 • 90 Star-shaped poly(styrene)-block-Poly(4-vinyl-N-methylpyridiniumiodide) for semipermanent antimicrobial coatings
Siedenbiedel, F. and Fuchs, A. and Moll, T. and Weide, M. and Breves, R. and Tiller, J.C.
Macromolecular Bioscience 13 1447-1455 (2013)Goal of the present work is to develop an antimicrobial coating that can be applied from an aqueous solution and resists short washing cycles, but can be rinsed off by thorough washing. To this end, a series of star-shaped polystyrene-block-poly(4-vinyl-N-methylpyridinium iodide) polymers are synthesized by anionic polymerization using a core-first approach. The optimal resulting polymers are applied as coatings on glass slides, showing high antimicrobial efficiency against Staphylococcus aureus as well as Escherichia coli. The coatings, characterized by atomic force microscopy and transmission electron microscopy, stay at the surface even after at least 20 flush-like washings with water, and retain their antimicrobial activity. Semipermanent antimicrobial coatings can be achieved by synthesizing 3-arm star-blockcopolymer with an inner poly(styrene)-block and an outer poly(4-vinyl-N-methylpyridiniumiodide)-block. Solubility, antimicrobial activity, and coating stability strongly depend on the block ratios. The coatings can be applied from aqueous solution, withstand flush-like washings and prevent growth of S. aureus and E. coli. Nonetheless, the coatings are removable of by extended rinsing. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/mabi.201300219 2013 • 89 To tilt or not to tilt: Correction of the distortion caused by inclined sample surfaces in low-energy electron diffraction
Sojka, F. and Meissner, M. and Zwick, C. and Forker, R. and Vyshnepolsky, M. and Klein, C. and Horn-von Hoegen, M. and Fritz, T.
Ultramicroscopy 133 35-40 (2013)Low-energy electron diffraction (LEED) is a widely employed technique for the structural characterization of crystalline surfaces and epitaxial adsorbates. For technical reasons the accessible reciprocal space is limited at a given primary electron energy E. This limitation may be overcome by sweeping E to observe higher diffraction orders decisively enhancing the quantitative examination. Yet, in many cases, such as molecular films with rather large unit cells, the adsorbate reflexes become less pronounced at energies high enough to observe substrate reflexes. One possibility to overcome this problem is an intentional inclination of the sample surface during the measurement at the expense of the quantitative interpretability of then severely distorted diffraction patterns. Here, we introduce a correction method for the axially symmetric distortion in LEED images of tilted samples. We provide experimental confirmation for micro-channel plate LEED and spot-profile analysis LEED instruments using the (7×7) reconstructed surface of a Si(111) single crystal as a reference sample. Finally, we demonstrate that the correction of this distortion considerably improves the quantitative analysis of diffraction patterns of adsorbates since substrate and adsorbate reflexes can be evaluated simultaneously. As an illustrative example we have chosen an epitaxial monolayer of 3,4,9,10-perylenetetracarboxylic dianhydride on Ag(111) that is known to form a commensurate superstructure. © 2013 Elsevier B.V.
view abstract doi: 10.1016/j.ultramic.2013.04.005 2013 • 88 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 • 87 The anodic stripping voltammetry of nanoparticles: Electrochemical evidence for the surface agglomeration of silver nanoparticles
Toh, H.S. and Batchelor-McAuley, C. and Tschulik, K. and Uhlemann, M. and Crossley, A. and Compton, R.G.
Nanoscale 5 4884-4893 (2013)Analytical expressions for the anodic stripping voltammetry of metallic nanoparticles from an electrode are provided. First, for reversible electron transfer, two limits are studied: that of diffusionally independent nanoparticles and the regime where the diffusion layers originating from each particle overlap strongly. Second, an analytical expression for the voltammetric response under conditions of irreversible electron transfer kinetics is also derived. These equations demonstrate how the peak potential for the stripping process is expected to occur at values negative of the formal potential for the redox process in which the surface immobilised nanoparticles are oxidised to the corresponding metal cation in the solution phase. This work is further developed by considering the surface energies of the nanoparticles and its effect on the formal potential for the oxidation. The change in the formal potential is modelled in accordance with the equations provided by Plieth [J. Phys. Chem., 1982, 86, 3166-3170]. The new analytical expressions are used to investigate the stripping of silver nanoparticles from a glassy carbon electrode. The relative invariance of the stripping peak potential at low surface coverages of silver is shown to be directly related to the surface agglomeration of the nanoparticles. © 2013 The Royal Society of Chemistry.
view abstract doi: 10.1039/c3nr00898c 2013 • 86 Formation of iron containing aggregates at the liquid-air interface
Wieland, D.C.F. and Degen, P. and Paulus, M. and Schroer, M.A. and Bieder, S. and Sahle, C.J. and Möller, J. and Leick, S. and Chen, Z. and Struth, B. and Rehage, H. and Tolan, M.
Colloids and Surfaces B: Biointerfaces 109 74-81 (2013)The early stages of the formation of inorganic aggregates, composed of iron compounds at the solution-air interface, were investigated in situ. The properties of the solution-air interface were changed by using different Langmuir layers. In order to get insight into the evolution of the sample system in situ, the processes were studied by X-ray scattering and spectroscopy techniques. The formation of aggregates was detected under cationic as well as under anionic Langmuir layers. The observed compounds lack long range order which indicates the formation of amorphous structures. This is supported by extended X-ray absorption fine structure measurements showing only minor order in the formed aggregates. © 2013 Elsevier B.V.
view abstract doi: 10.1016/j.colsurfb.2013.03.006 2013 • 85 Slippery liquid-infused porous surfaces showing marine antibiofouling properties
Xiao, L. and Li, J. and Mieszkin, S. and Di Fino, A. and Clare, A.S. and Callow, M.E. and Callow, J.A. and Grunze, M. and Rosenhahn, A. and Levkin, P.A.
ACS Applied Materials and Interfaces 5 10074-10080 (2013)Marine biofouling is a longstanding problem because of the constant challenges placed by various fouling species and increasingly restricted environmental regulations for antifouling coatings. Novel nonbiocidal strategies to control biofouling will necessitate a multifunctional approach to coating design. Here we show that slippery liquid-infused porous surfaces (SLIPSs) provide another possible strategy to obtaining promising antifouling coatings. Microporous butyl methacrylate-ethylene dimethacrylate (BMA-EDMA) surfaces are prepared via UV-initiated free-radical polymerization. Subsequent infusion of fluorocarbon lubricants (Krytox103, Krytox100, and Fluorinert FC-70) into the porous microtexture results in liquid-repellent slippery surfaces. To study the interaction with marine fouling organisms, settlement of zoospores of the alga Ulva linza and cypris larvae of the barnacle Balanus amphitrite is tested in laboratory assays. BMA-EDMA surfaces infused with Krytox103 and Krytox100 exhibit remarkable inhibition of settlement (attachment) of both spores and cyprids to a level comparable to that of a poly(ethylene glycol) (PEG)-terminated self-assembled monolayer. In addition, the adhesion strength of sporelings (young plants) of U. linza is reduced for BMA-EDMA surfaces infused with Krytox103 and Krytox100 compared to pristine (noninfused) BMA-EDMA and BMA-EDMA infused with Fluorinert FC-70. Immersion tests suggest a correlation between the stability of slippery coatings in artificial seawater and fouling resistance efficacy. The results indicate great potential for the application of this concept in fouling-resistant marine coatings. © 2013 American Chemical Society.
view abstract doi: 10.1021/am402635p 2013 • 84 Hot embossed microtopographic gradients reveal morphological cues that guide the settlement of zoospores
Xiao, L. and Thompson, S.E.M. and Röhrig, M. and Callow, M.E. and Callow, J.A. and Grunze, M. and Rosenhahn, A.
Langmuir 29 1093-1099 (2013)Among different surface cues, the settlement of cells and larvae of marine macrofouling organisms has been found to be strongly influenced by surface microtopographies. In this article, the settlement of zoospores of the green alga Ulva linza on a surface topographic gradient has been investigated. "Honeycomb" gradient structures with feature sizes ranging from 1 to 10 μm were prepared by hot embossing, and the effect on the density of spores that attached in settlement assays was quantified. The highest density of spores was found when the size of the microstructures was similar to or larger than the size of the spores. With decreasing size of the structures, spore settlement density decreased. Interestingly, spore settlement density correlated with the Wenzel roughness of the surfaces. "Kink sites" on the surface played an important role and resembled preferred attachment positions. Furthermore, the gradients allowed the minimum pit size that the spores were able to squeeze into to be determined. © 2012 American Chemical Society.
view abstract doi: 10.1021/la303832u 2013 • 83 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 • 82 Antibody-imprinted membrane adsorber via two-step surface grafting
Yin, D. and Ulbricht, M.
Biomacromolecules 14 4489-4496 (2013)In this work, a recently established, novel two-step imprinting strategy combining surface imprinting and scaffold imprinting was applied successfully to prepare a molecularly imprinted polymer (MIP) adsorber for immunoglobulin G (IgG). Track-etched polyethylene terephthalate (PET) membranes with previously introduced aliphatic C-Br groups as initiator on the pore surface were used to prepare first a functional polymer scaffold, grafted poly(methacrylic acid), via surface-initiated atom transfer radical polymerization (SI-ATRP). After template protein (IgG) binding to the scaffold, UV-initiated cross-linking copolymerization of acrylamide and methylenebisacrylamide (MBAA) as second step lead to a grafted MIP hydrogel layer. The influences of the three independent parameters, scaffold chain length by SI-ATRP time, degree of cross-linking of the MIP layer by MBAA content, and grafted MIP layer thickness by UV irradiation time, were studied to optimize protein binding capacity and selectivity. The results were also compared to previously obtained data for lysozyme imprinting using the same method, and significant effects of protein size on imprinting efficiency could be identified. The best IgG MIP membrane adsorber was then used to separate IgG from mixtures with human serum albumin (HSA), demonstrating IgG binding capacities and eluted IgG purities, which were almost independent of the excess of HSA. The results of this study are a significant extension of the scope of molecular imprinting toward large target bionanoparticles. The transfer of the approach from the model PET to other base membranes with higher specific surface area is straightforward, and the resulting affinity materials would, in principle, be suited for "capturing" of an antibody from a complex mixture. © 2013 American Chemical Society.
view abstract doi: 10.1021/bm401444y 2012 • 81 Microfluidic assay to quantify the adhesion of marine bacteria
Arpa-Sancet, M.P. and Christophis, C. and Rosenhahn, A.
Biointerphases 7 1-9 (2012)For both, environmental and medical applications, the quantification of bacterial adhesion is of major importance to understand and support the development of new materials. For marine applications, the demand is driven by the quest for improved fouling-release coatings. To determine the attachment strength of bacteria to coatings, a microfluidic adhesion assay has been developed which allows probing at which critical wall shear stress bacteria are removed from the surface. Besides the experimental setup and the optimization of the assay, we measured adhesion of the marine bacterium Cobetia marina on a series of differently terminated self-assembled monolayers. The results showed that the adhesion strength of C. marina changes with surface chemistry. The difference in critical shear stress needed to remove bacteria can vary by more than one order of magnitude if a hydrophobic material is compared to an inert chemistry such as polyethylene glycol. © The Author(s) 2012.
view abstract doi: 10.1007/s13758-012-0026-x 2012 • 80 Self-cleaning functional molecular materials
Avinash, M.B. and Verheggen, E. and Schmuck, C. and Govindaraju, T.
Angewandte Chemie - International Edition 51 10324-10328 (2012)Clean and polish: The spontaneous hierarchical molecular assembly of a naphthalenediimide derivative is used to form microarrays by a simple solution-processing technique. This method is further employed to fabricate a self-cleaning surface with very low slide angle (3°) and contact angle hysteresis (1°). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/anie.201204608 2012 • 79 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 • 78 UV-photo graft functionalization of polyethersulfone membrane with strong polyelectrolyte hydrogel and its application for nanofiltration
Bernstein, R. and Antón, E. and Ulbricht, M.
ACS Applied Materials and Interfaces 4 3438-3446 (2012)A strong polyelectrolyte hydrogel was graft copolymerized on a polyethersulfone (PES) ultrafiltration (UF) membrane using vinyl sulfonic acid (VSA) as the functional monomer, and N,N′-methylenbisacrylamide (MBAA) as the cross-linker monomer. This was carried out in one simple step using the UV photoirradiation method. The effect of the polymerization conditions on the degree of grafting (DG) was investigated using the gravimetric method which measures the total hydrogel grafted on the membrane, and with ATR-FTIR spectroscopy which indicates the functional monomer fraction in the hydrogel layer. The VSA could not graft polymerize without the cross-linker as comonomer. An increase in the cross-linker fraction from 0.25 to 2.5 mol % (relative to the functional monomer VSA) resulted in a higher DG. Although the surface morphology changed upon modification, the resulting surface roughness as measured by AFM was very low. From the monitoring of DG with UV time (4.5-30 min) at constant conditions, it was deduced that during the early stages of the polymerization mainly the cross-linker was grafted, thus inducing the graft copolymerization of the functional monomer. Polymerization using a higher monomer concentration (12.5-40% VSA) at constant monomer/cross-linker ratio resulted in a higher VSA fraction in the grafted hydrogel, although the gravimetric DG was similar. Ion exchange capacity and X-ray photoelectron spectroscopy measured after modification under the different conditions supported these findings. The new membranes were tested under nanofiltration (NF) conditions. A NF membrane could be obtained when the MBAA fraction was above 0.25%. The Na 2SO 4 rejection was 90-99% and the permeability 10-1 L m -2 h -1 bar -1 when the MBAA fraction increased from 0.75 to 2.5%. The order of rejection of single salts solution was Na 2SO 4 > MgSO 4 ≈ NaCl > CaCl 2, as expected on the basis of Donnan exclusion for negatively charged NF membranes. An increase in the salts rejection with increasing degree of cross-linking and VSA fraction was attributed to an increase in the membrane charge density and to steric exclusion that also resulted in an increase of rejection for uncharged solutes such as sucrose or glucose. The new membrane presented a high, essentially unchanged Na 2SO 4 rejection (>97%) in the range of salt concentrations up to 4 g/L, and only slightly reduced rejection (>92%) at a concentration of 8 g/L; this can be related to its high barrier layer charge density measured by ion exchange capacity. In addition, because poly(vinyl sulfonic acid) (PVSA) is a strong polyelectrolyte the membrane separation performance was stable in the range of pH 1.5 to pH 10. © 2012 American Chemical Society.
view abstract doi: 10.1021/am300426c 2012 • 77 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 • 76 Experimental investigation on micromilling of austenitic stainless steel
Biermann, D. and Steiner, M.
International Journal of Nanomanufacturing 8 184-201 (2012)This paper presents the results of experimental investigations on the micro-machinability of the austenitic stainless steel 1.4301 under dry cutting conditions. Two different types of coated carbide micro end-milling cutters with a diameter of d = 1 mm were used. Applying a central composite design for the experimental investigations, the effects of the process parameters cutting speed v c, depth of cut a p, width of cut a e and feed per tooth f z on the process forces were analysed. It was found that the cutting speed v c had nearly no influence on the active force F a. The feed per tooth f z is the major factor influencing the active force F a for the defined parameter range. The achievable surface roughness and the tool wear were analysed as well. Based on the experimental results a range for suitable cutting parameters was identified and a comparison of two different tool designs was done. Copyright © 2012 Inderscience Enterprises Ltd.
view abstract doi: 10.1504/IJNM.2012.047020 2012 • 75 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 • 74 Influence of surface characteristics on fatigue behaviour of laser sintered plastics
Blattmeier, M. and Witt, G. and Wortberg, J. and Eggert, J. and Toepker, J.
Rapid Prototyping Journal 18 161-171 (2012)Purpose - The purpose of this paper is to provide macromechanical insight into the fatigue behaviour of laser sintered parts and to understand the influence of the laser sintered surface structure on this behaviour. Design/methodology/approach - A background on the technological maturity of manufacturing processes and the demand for structural and aesthetic properties of laser sintered plastic products is given. As the contribution of surface structure on part quality was the focus, laser sintered specimens with and without surface finishes, as well as injection moulded specimens were used. The latter simply served as a comparison and was not intended to qualify injection moulding. The study comprises the determination of short-term tensile properties, the load increase method for investigating fracture and deformation behaviours, and fatigue crack propagation analysis. Findings - According to the test results, the contribution of laser sintered surface structures to relevant mechanical properties can be neglected. Under dynamic loading conditions, laser sintered specimens achieved a longer lifetime but showed less deformation capabilities in contrast to injection moulded specimens. In general, laser sintered specimens presented considerable resistance to crack initiation and propagation. Research limitations/implications - Because of the long-term approach of the research, the number of tests conducted per lot was limited. Thus, the effects of different process settings and the reproducibility could not be fully analysed. Practical implications - The studied fatigue behaviour of laser sintered specimens has implications for the functional testing of parts or components, for the product and process design as well as for the general compatibility of laser sintering as a manufacturing technology of end-customer products. Originality/value - The value of this paper lies in the better understanding of deformation and fracture behaviours of laser sintered polymers. © 2012 Emerald Group Publishing Limited.
view abstract doi: 10.1108/13552541211212140 2012 • 73 Synthesis of high surface area ZnO powder by continuous precipitation
Boz, I. and Kaluza, S. and Boroǧlu, M.S. and Muhler, M.
Materials Research Bulletin 47 1185-1190 (2012)Synthesis of high surface area ZnO powder was achieved by continuous precipitation using zinc ions and urea at low temperature of 90 °C. The powder precipitated resulted in high-purity single-phase ZnO powder when calcined at 280 °C for 3 h in air. The solution pH and the precipitation duration strongly affected the surface area of the calcined ZnO powder. Detailed structural characterizations demonstrated that the synthesized ZnO powder were single crystalline with wurtzite hexagonal phase. The powdered samples precipitated by homogeneous precipitation crystallized directly to hydrozincite without any intermediate phase formation. The phase structures, morphologies and properties of the final ZnO powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), dynamic light scattering particle size analysis (DLS), and nitrogen physisorption in order to determine the specific surface area (BET) and the pore size distribution (BJH). © 2012 Elsevier Ltd. All rights reserved.
view abstract doi: 10.1016/j.materresbull.2012.02.005 2012 • 72 Preparation of 24 ternary thin film materials libraries on a single substrate in one experiment for irreversible high-throughput studies
Buenconsejo, P.J.S. and Siegel, A. and Savan, A. and Thienhaus, S. and Ludwig, Al.
ACS Combinatorial Science 14 25-30 (2012)For different areas of combinatorial materials science, it is desirable to have multiple materials libraries: especially for irreversible high-throughput studies, like, for example, corrosion resistance testing in different media or annealing of complete materials libraries at different temperatures. Therefore a new combinatorial sputter-deposition process was developed which yields 24 materials libraries in one experiment on a single substrate. It is discussed with the example of 24 Ti-Ni-Ag materials libraries. They are divided based on the composition coverage and orientation of composition gradient into two sets of 12 nearly identical materials libraries. Each materials library covers at least 30-40% of the complete ternary composition range. An acid etch test in buffered-HF solution was performed, illustrating the feasibility of our approach for destructive materials characterization. The results revealed that within the composition range of Ni < 30 at.%, the films were severely etched. The composition range which shows reversible martensitic transformations was confirmed to be outside this region. The high output of the present method makes it attractive for combinatorial studies requiring multiple materials libraries. © 2011 American Chemical Society.
view abstract doi: 10.1021/co2001263 2012 • 71 Microstructural impact of anodic coatings on the electrochemical chlorine evolution reaction
Chen, R. and Trieu, V. and Zeradjanin, A.R. and Natter, H. and Teschner, D. and Kintrup, J. and Bulan, A. and Schuhmann, W. and Hempelmann, R.
Physical Chemistry Chemical Physics 14 7392-7399 (2012)Sol-gel Ru 0.3Sn 0.7O 2 electrode coatings with crack-free and mud-crack surface morphology deposited onto a Ti-substrate are prepared for a comparative investigation of the microstructural effect on the electrochemical activity for Cl 2 production and the Cl 2 bubble evolution behaviour. For comparison, a state-of-the-art mud-crack commercial Ru 0.3Ti 0.7O 2 coating is used. The compact coating is potentially durable over a long term compared to the mud-crack coating due to the reduced penetration of the electrolyte. Ti L-edge X-ray absorption spectroscopy confirms that a TiO x interlayer is formed between the mud-crack Ru 0.3Sn 0.7O 2 coating and the underlying Ti-substrate due to the attack of the electrolyte. Meanwhile, the compact coating shows enhanced activity in comparison to the commercial coating, benefiting from the nanoparticle-nanoporosity architecture. The dependence of the overall electrode polarization behaviour on the local activity and the bubble evolution behaviour for the Ru 0.3Sn 0.7O 2 coatings with different surface microstructure are evaluated by means of scanning electrochemical microscopy and microscopic bubble imaging. © 2012 the Owner Societies.
view abstract doi: 10.1039/c2cp41163f 2012 • 70 A facile route to reassemble titania nanoparticles into ordered chain-like networks on substrate
Cheng, Y.-J. and Wolkenhauer, M. and Bumbu, G.-G. and Gutmann, J.S.
Macromolecular Rapid Communications 33 218-224 (2012)A facile route to reassemble titania nanoparticles within the titania-block copolymer composite films has been developed. The titania nanoparticles templated by the amphiphilic block copolymer of poly(styrene)-block-poly (ethylene oxide) (PS-b-PEO) were frozen in the continuous PS matrix. Upon UV exposure, the PS matrix was partially degraded, allowing the titania nanoparticles to rearrange into chain-like networks exhibiting a closer packing. The local structures of the Titania chain-like networks were investigated by both AFM and SEM; the lateral structures and vertical structures of the films were studied by GISAXS and X-ray reflectivity respectively. Both the image analysis and X-ray scattering characterization prove the reassembly of the titania nanoparticles after UV exposure. The mechanism of the nanoparticle assembly is discussed. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/marc.201100638 2012 • 69 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 • 68 Understanding properties of electrified interfaces as a prerequisite for label-free DNA hybridization detection
Gebala, M. and Schuhmann, W.
Physical Chemistry Chemical Physics 14 14933-14942 (2012)Label-free electrochemical detection of DNA hybridization with high selectivity and sensitivity is only achievable if the properties of DNA at an electrified interface are understood in depth. After a short summary of concepts of electrochemical DNA detection as well as initial attempts towards label-free DNA assays the review discusses the physico-chemical properties and differences between single-stranded and double-stranded DNA immobilized at electrode surfaces in the light of their persistence lengths, structural conformation, impact of the charge screening by ion condensation and the electric field generated upon polarization of the electrode. Electrochemical impedance spectroscopy as a tool for label-free elucidation of DNA hybridization is reviewed and the necessity for an in-depth understanding of the interfacial properties is highlighted. Our major aim is to demonstrate the advantageous application of specifically designed intercalating compounds for the design of label-free detection of DNA hybridization. This journal is © 2012 the Owner Societies.
view abstract doi: 10.1039/c2cp42382k 2012 • 67 Subsurface influence on the structure of protein adsorbates as revealed by in situ X-ray reflectivity
Hähl, H. and Evers, F. and Grandthyll, S. and Paulus, M. and Sternemann, C. and Loskill, P. and Lessel, M. and Hüsecken, A.K. and Brenner, T. and Tolan, M. and Jacobs, K.
Langmuir 28 7747-7756 (2012)The adsorption process of proteins to surfaces is governed by the mutual interactions among proteins, the solution, and the substrate. Interactions arising from the substrate are usually attributed to the uppermost atomic layer. This actual surface defines the surface chemistry and hence steric and electrostatic interactions. For a comprehensive understanding, however, the interactions arising from the bulk material also have to be considered. Our protein adsorption experiments with globular proteins (α-amylase, bovine serum albumin, and lysozyme) clearly reveal the influence of the subsurface material via van der Waals forces. Here, a set of functionalized silicon wafers enables a distinction between the effects of surface chemistry and the subsurface composition of the substrate. Whereas the surface chemistry controls whether the individual proteins are denatured, the strength of the van der Waals forces affects the final layer density and hence the adsorbed amount of proteins. The results imply that van der Waals forces mainly influence surface processes, which govern the structure formation of the protein adsorbates, such as surface diffusion and spreading. © 2012 American Chemical Society.
view abstract doi: 10.1021/la300850g 2012 • 66 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 • 65 Settlement behavior of zoospores of Ulva linza during surface selection studied by digital holographic microscopy
Heydt, M. and Pettitt, M.E. and Cao, X. and Callow, M.E. and Callow, J.A. and Grunze, M. and Rosenhahn, A.
Biointerphases 7 1-7 (2012)Settlement of the planktonic dispersal stages of marine organisms is the crucial step for the development of marine biofouling. Four-dimensional holographic tracking reveals the mechanism by which algal spores select surfaces suitable for colonization. Quantitative analysis of the three dimensional swimming trajectories of motile spores of a macroalga (Ulva linza) in the vicinity of surfaces functionalized with different chemistries reveals that their search strategy and swimming behavior is correlated to the number of settled spores found in spore settlement bioassays conducted over 45 min. The spore motility and exploration behavior can be classified into different motion patterns, with their relative occurrence changing with the surface chemistry. Based on the detailed motility analysis we derived a model for the surface selection and settlement process of Ulva zoospores. © The Author(s) 2012.
view abstract doi: 10.1007/s13758-012-0033-y 2012 • 64 Impact of single basepair mismatches on electron-transfer processes at Fc-PNA·DNA modified gold surfaces
Hüsken, N. and Gȩbala, M. and Battistel, A. and La Mantia, F. and Schuhmann, W. and Metzler-Nolte, N.
ChemPhysChem 13 131-139 (2012)Gold-surface grafted peptide nucleic acid (PNA) strands, which carry a redox-active ferrocene tag, present unique tools to electrochemically investigate their mechanical bending elasticity based on the kinetics of electron-transfer (ET) processes. A comparative study of the mechanical bending properties and the thermodynamic stability of a series of 12-mer Fc-PNA·DNA duplexes was carried out. A single basepair mismatch was integrated at all possible strand positions to provide nanoscopic insights into the physicochemical changes provoked by the presence of a single basepair mismatch with regard to its position within the strand. The ET processes at single mismatch Fc-PNA·DNA modified surfaces were found to proceed with increasing diffusion limitation and decreasing standard ET rate constants k 0 when the single basepair mismatch was dislocated along the strand towards its free-dangling Fc-modified end. The observed ET characteristics are considered to be due to a punctual increase in the strand elasticity at the mismatch position. The kinetic mismatch discrimination with respect to the fully-complementary duplex presents a basis for an electrochemical DNA sensing strategy based on the Fc-PNA·DNA bending dynamics for loosely packed monolayers. In a general sense, the strand elasticity presents a further physicochemical property which is affected by a single basepair mismatch which may possibly be used as a basis for future DNA sensing concepts for the specific detection of single basepair mismatches. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/cphc.201100578 2012 • 63 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 • 62 Surface functionalization of mesoporous antimony doped tin oxide by metalorganic reaction
Müller, V. and Haase, F. and Rathousky, J. and Fattakhova-Rohlfing, D.
Materials Chemistry and Physics 137 207-212 (2012)Electrically conducting mesoporous antimony doped tin oxide was functionalized by the metalorganic reaction with several Grignard reagents. This fast and efficient grafting approach enables a direct connection of the metal atoms with the organic functionalities avoiding the formation of insulating Si-O linkers, which is of special interest for the interfacial charge transfer processes. Using this approach we introduced vinyl, allyl and phenyl groups into the pores of mesoporous ATO, which was confirmed by IR spectroscopy, TGA and nitrogen sorption measurements. We obtained a high loading of organic groups corresponding to about 50-60% of the monolayer surface coverage. The obtained mesoporous inorganic-organic hybrids can serve as a platform for incorporation of electrochemically active species. © 2012 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.matchemphys.2012.09.008 2012 • 61 Interface of nanoparticle-coated electropolished stents
Neumeister, A. and Bartke, D. and Bärsch, N. and Weingärtner, T. and Guetaz, L. and Montani, A. and Compagnini, G. and Barcikowski, S.
Langmuir 28 12060-12066 (2012)Nanostructures entail a high potential for improving implant surfaces, for instance, in stent applications. The electrophoretic deposition of laser-generated colloidal nanoparticles is an appropriate tool for creating large-area nanostructures on surfaces. Until now, the bonding and characteristics of the interface between deposited nanoparticles and the substrate surface has not been known. It is investigated using X-ray photoelectron spectroscopy, Auger electron spectroscopy, and transmission electron microscopy to characterize an electropolished NiTi stent surface coated by laser-generated Au and Ti nanoparticles. The deposition of elemental Au and Ti nanoparticles is observed on the total 3D surface. Ti-coated samples are composed of Ti oxide and Ti carbide because of nanoparticle fabrication and the coating process carried out in 2-propanol. The interface between nanoparticles and the electropolished surface consists of a smooth, monotone elemental depth profile. The interface depth is higher for the Ti nanoparticle coating than for the Au nanoparticle coating. This smooth depth gradient of Ti across the coating-substrate intersection and the thicker interface layer indicate the hard bonding of Ti-based nanoparticles on the surface. Accordingly, electron microscopy reveals nanoparticles adsorbed on the surface without any sorption-blocking intermediate layer. The physicomechanical stability of the bond may benefit from such smooth depth gradients and direct, ligand-free contact. This would potentially increase the coating stability during stent application. © 2012 American Chemical Society.
view abstract doi: 10.1021/la300308w 2012 • 60 Stress-structure correlation in ps-pmma mixed polymer brushes
Ochsmann, J.W. and Lenz, S. and Lellig, P. and Emmerling, S.G.J. and Golriz, A.A. and Reichert, P. and You, J. and Perlich, J. and Roth, S.V. and Berger, R. and Gutmann, J.S.
Macromolecules 45 3129-3136 (2012)The ability to alter surface properties such as morphology and surface energy upon external stimuli makes switchable polymer surfaces a promising field of research. Mixed polymer brushes consisting of two different homopolymers covalently attached to a surface are one system in which surface properties can be switched. In this work the correlation between the change in structure and the resulting surface stress in thin poly(methyl methacrylate)-polystyrene mixed polymer brush film upon exposure to selective solvents is investigated. By measuring the forces acting inside the film, we are able to achieve a deeper understanding of the observed structural changes. To obtain a thorough understanding of the film's morphology, the structure is analyzed by scanning probe microscopy, X-ray reflectivity, and grazing incidence small-angle X-ray scattering (GISAXS). Upon exposure to acetic acid, a selective solvent for PMMA, the film showed a dimple-like structure. This is linked to collapsed domains of polystyrene covered by PMMA chains. Bending experiments resulted in tensile stress, pointing to attractive forces acting inside the polymer film. After exposure to dichloromethane, a good solvent for both polymers, bending experiments revealed a decreased but still high tensile stress, indicating that the microdomains are still present. The results of the experiments enable us to further explain the domain memory effect typically found in these kinds of mixed polymer brush systems. © 2012 American Chemical Society.
view abstract doi: 10.1021/ma2025286 2012 • 59 Enhanced performance of surface-modified TiO2 photocatalysts prepared via a visible-light photosynthetic route
Ramakrishnan, A. and Neubert, S. and Mei, B. and Strunk, J. and Wang, L. and Bledowski, M. and Muhler, M. and Beranek, R.
Chemical Communications 48 8556-8558 (2012)Benzene can be activated by visible light (λ > 455 nm) in the presence of TiO2, which leads to formation of carbonaceous polymeric deposits on the titania surface. These photosynthesized surface-modified materials exhibit enhanced photoactivity in degradation of phenolic compounds, particularly under visible light irradiation. © 2012 The Royal Society of Chemistry.
view abstract doi: 10.1039/c2cc34243j 2012 • 58 Improvement in mechanical properties of jute fibres through mild alkali treatment as demonstrated by utilisation of the Weibull distribution model
Roy, A. and Chakraborty, S. and Kundu, S.P. and Basak, R.K. and Basu Majumder, S. and Adhikari, B.
Bioresource Technology 107 222-228 (2012)Chemically modified jute fibres are potentially useful as natural reinforcement in composite materials. Jute fibres were treated with 0.25%-1.0% sodium hydroxide (NaOH) solution for 0.5-48. h. The hydrophilicity, surface morphology, crystallinity index, thermal and mechanical characteristics of untreated and alkali treated fibres were studied.The two-parameter Weibull distribution model was applied to deal with the variation in mechanical properties of the natural fibres. Alkali treatment enhanced the tensile strength and elongation at break by 82% and 45%, respectively but decreased the hydrophilicity by 50.5% and the diameter of the fibres by 37%. © 2011 Elsevier Ltd.
view abstract doi: 10.1016/j.biortech.2011.11.073 2012 • 57 Conditioning of surfaces by macromolecules and its implication for the settlement of zoospores of the green alga Ulva linza
Thome, I. and Pettitt, M.E. and Callow, M.E. and Callow, J.A. and Grunze, M. and Rosenhahn, A.
Biofouling 28 501-510 (2012)Conditioning, ie the adsorption of proteins and other macromolecules, is the first process that occurs in the natural environment once a surface is immersed in seawater, but no information is available either regarding the conditioning of surfaces by artificial seawater or whether conditioning affects data obtained from laboratory assays. A range of self-assembled monolayers (SAMs) with different chemical terminations was used to investigate the time-dependent formation of conditioning layers in commercial and self-prepared artificial seawaters. Subsequently, these results were compared with conditioning by solutions in which zoospores of the green alga Ulva linza had been swimming. Spectral ellipsometry and contact angle measurements as well as infrared reflection absorption spectroscopy (IRRAS) were used to reveal the thickness and chemical composition of the conditioning layers. The extent that surface preconditioning affected the settlement of zoospores of U. linza was also investigated. The results showed that in standard spore settlement bioassays (45-60 min), the influence of a molecular conditioning layer is likely to be small, although more substantial effects are possible at longer settlement times. © 2012 Copyright Taylor and Francis Group, LLC.
view abstract doi: 10.1080/08927014.2012.689288 2012 • 56 Evaluation of the catalytic performance of gas-evolving electrodes using local electrochemical noise measurements
Zeradjanin, A.R. and Ventosa, E. and Bondarenko, A.S. and Schuhmann, W.
ChemSusChem 5 1905-1911 (2012)Characterization of gas evolution reactions at the electrode/electrolyte boundary is often difficult due to the dynamic behavior of interfacial processes. Electrochemical noise measurements determined by scanning electrochemical microscopy were used to characterize Cl 2 evolution at gas-evolving electrodes (GEEs). Analysis of the electrochemical noise is a powerful method to evaluate the efficiency of the catalyst layer at a GEE. The high sensitivity of the developed measurement system enabled accurate monitoring of the current fluctuations caused by gas-bubble detachment from the electrode surface. Fourier transform analysis of the obtained current responses allows extraction of the characteristic frequency, which is the main parameter of the macrokinetics of GEEs. The characteristic frequency was used as part of a methodology to evaluate the catalyst performance and, in particular, to estimate the fraction of the catalyst layer that is active during the gas evolution reaction. Tip of the iceberg: Positioned scanning electrochemical microscopy tips are used to determine the characteristic frequency of gas-bubble detachment from ruthenium-based dimensionally stable anodes at different applied potentials (see picture). Geometrical factors and optimized microstructures of the electrode surface are essential for improving the overall catalytic activity for industrial applications. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/cssc.201200262 2011 • 55 Photo-chemical surface modification for the control of protein adsorption on textile substrates
Bahners, T. and Klingelhöller, K. and Ulbricht, M. and Wego, A. and Schollmeyer, E.
Journal of Adhesion Science and Technology 25 2219-2238 (2011)Cell growth on fiber surfaces is an important aspect of many applications of technical textiles. The need to prevent clogging in artificial blood vessels or in textiles used for blood or water filtration as well as the anti-fouling properties of outdoor technical textiles are examples in this context. Since the adsorption of proteins forms the initial step of cell growth, a promising way to avoid biofouling is to prohibit protein adsorption by means of a suitable, permanent and non-toxic surface functionalization. Today, the deposition of poly(ethylene glycol)s (PEGs) is a well-known approach to decrease non-specific protein adsorption. In this work, a photo-chemical method to graft or cross-link PEGs on fiber surfaces was studied. Monomethacrylated PEG300MA and PEG2080MA as well as dimethacrylated PEG400DMA and PEG600DMA were considered, the numbers indicate average molar mass in g/mol. Textile fabrics made of poly(ethylene terephthalate) (PET) were impregnated with solutions of the PEGs and irradiated using either a KrCl* or a XeCl* excimer lamp (emission wavelengths 222 or 308 nm, respectively). Surface properties of the treated textiles were characterized as a function of process conditions using various surface sensitive analyses. UV cross-linking of PEG400DMA resulted in the deposition of a thick layer which effectively masked the texture of the fabric and its pore system. Much less coverage was observed in case of monomethacrylated PEGMAs, with a significant reduction in drop penetration time already after deposition of a marginal layer (less than 0.01 mg/mg). Highest reductions in adsorption of bovine serum albumin (BSA) were observed for samples prepared using PEG300MA or PEG400DMA under conditions where also the drop penetration time was at its minimum. The longer chain PEG2080MA was less effective. All results show clearly that the protein adsorption tendency can be significantly reduced by choice of suitable combinations of PEGylated monomer and UV irradiation conditions. © 2011 Koninklijke Brill NV, Leiden.
view abstract doi: 10.1163/016942411X574925 2011 • 54 Light driven reactions of single physisorbed azobenzenes
Bazarnik, M. and Henzl, J. and Czajka, R. and Morgenstern, K.
Chemical Communications 47 7764-7766 (2011)We present a successful attempt of decoupling a dye molecule from a metallic surface via physisorption for enabling direct photoisomerization. Effective switching between the isomers is possible by exposure to UV light via the rotation pathway. © 2011 The Royal Society of Chemistry.
view abstract doi: 10.1039/c1cc11578b 2011 • 53 Contact-Active Antimicrobial and Potentially Self-Polishing Coatings Based on Cellulose
Bieser, A.M. and Thomann, Y. and Tiller, J.C.
Macromolecular Bioscience 11 111-121 (2011)A contact-active antimicrobial coating is described that is only degraded in the presence of cellulase, which is an extracellular enzyme of numerous microbial strains. Antimicrobial DDA was grafted to a cellulose backbone via a polymeric spacer. The antimicrobial activity of the coatings, their biodegradability and their self-polishing potential were investigated. It was found that all coatings were antimicrobially active against Staphylococcus aureus. Coatings with high DS and long polymeric spacers degraded in water, while coatings with low DS and short spacers were not hydrolyzed even in the presence of cellulase. One coating was found to be selectively degradable by cellulase and recovered most of its antimicrobial activity after overloading and subsequent treatment with cellulase. A stable coating is presented that can kill microbes on contact and is potentially self-polishing only in the presences of these microbes. This is realized by grafting antimicrobial quarternary ammonium groups via polymeric spacers made of poly(2-ethyl-1,3-oxazoline)s on a cellulose backbone. With optimum DS and spacer length, this derivative is indeed contact-active antimicrobial against S. aureus and E. coli and degradable by the enzyme cellulase. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/mabi.201000306 2011 • 52 Photomodulation of the magnetisation of Co nanocrystals decorated with Rhodamine B
Comesaña-Hermo, M. and Estivill, R. and Ciuculescu, D. and Amiens, C. and Farle, M. and Batat, P. and Jonusauskas, G. and McClenaghan, N.D. and Lecante, P. and Tardin, C. and Mazeres, S.
ChemPhysChem 12 2915-2919 (2011)How exciting! Upon excitation of Rhodamine B with visible light in magnetic Co nanocrystal-Rhodamine B nanocomposites, electron transfer from the nanocrystal to the dye is evidenced as well as an increase in magnetisation (see picture), affording a new access to photomodulation of the magnetic properties of nanocrystal assemblies. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/cphc.201100616 2011 • 51 Solid-solid interface adsorption of proteins and enzymes in nanophase-separated amphiphilic conetworks
Dech, S. and Cramer, T. and Ladisch, R. and Bruns, N. and Tiller, J.C.
Biomacromolecules 12 1594-1601 (2011)Amphiphilic polymer conetworks (APCNs) are materials with a very large interface between their hydrophilic and hydrophobic phases due to their nanophase-separated morphologies. Proteins were found to enrich in APCNs by up to 2 orders of magnitude when incubated in aqueous protein solutions, raising the question of the driving force of protein uptake into APCNs. The loading of poly(2-hydroxyethyl acrylate)-linked by-poly(dimethylsiloxane) (PHEA-l-PDMS) with heme proteins (myoglobin, horseradish peroxidase, hemoglobin) and lipases was studied under variation of parameters such as incubation time, pH, concentration of the protein solution, and conetwork composition. Adsorption of enzymes to the uncharged interface is the main reason for protein uptake, resulting in protein loading of up to 23 wt %. Experimental results were supported by computation of electrostatic potential maps of a lipase, indicating that hydrophobic patches are responsible for the adsorption to the interface. The findings underscore the potential of enzyme-loaded APCNs in biocatalysis and as sensors. © 2011 American Chemical Society.
view abstract doi: 10.1021/bm1015877 2011 • 50 Chemical and physical factors in design of antibiofouling polymer coatings
Eshet, I. and Freger, V. and Kasher, R. and Herzberg, M. and Lei, J. and Ulbricht, M.
Biomacromolecules 12 2681-2685 (2011)Because most "low fouling" polymers resisting bacterial attachment are hydrophilic, they are usually also significantly swollen. Swelling leads to purely physical dilution of interaction and weakens attachment; however, these nonspecific contributions are usually not separated from the specific effect of polymer chemistry. Taking advantage of the fact that chemistry and swelling of hydrogels may be independently varied through the fraction of a cross-linker, the roles of chemistry and physical dilution (swelling) in bacterial attachment are analyzed for selected hydrogels. Using as a quantitative indicator the rate of bacterial deposition in a parallel plate setup under defined flow conditions, the observed correlation of deposition rate with swelling provides a straightforward comparison of gels with different chemistries that can factor out the effect of swelling. In particular, it is found that chemistry appears to contribute similarly to bacterial deposition on hydrogels prepared from acrylamide and a zwitterioninic monomer 2-(methacryloyloxy)ethyl) dimethyl-(3-sulfopropyl) ammonium hydroxide so that the observed differences may be related to swelling only. In contrast, these gels were inferior to PEG-based hydrogels, even when swelling of the latter was lower, indicating a greater contribution of PEG chemistry to reduced bacterial deposition. This demonstrates that swelling must be accounted for when comparing different biofouling-resistant materials. Chemical and physical principles may be combined in hydrogel coatings to develop efficient antibiofouling surfaces. © 2011 American Chemical Society.
view abstract doi: 10.1021/bm200476g 2011 • 49 Ultrahigh-aspect ratio microfiber-furs as plant-surface mimics derived from teeth
Fik, C.P. and Meuris, M. and Salz, U. and Bock, T. and Tiller, J.C.
Advanced Materials 23 3565-3569 (2011)Ultrahydrophobic surfaces that mimic the surface of a Corokia cotoneaster leaf were created by using cow teeth as natural template. After UV curing of an acrylate resin and removing the template, a highly dense hairy fur-like structure with high aspect ratio could be obtained. Subsequent modification with silica nanoparticles and fluorosilane afforded a water contact angle of some 170°. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/adma.201101102 2011 • 48 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 • 47 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 • 46 Preparation of thermo-responsive polypropylene membranes via surface entrapment of poly(N-isopropylacrylamide)-containing macromolecules
Guo, H. and Ulbricht, M.
Journal of Membrane Science 372 331-339 (2011)Thermo-responsive polypropylene (PP) microfiltration membranes have been fabricated via surface entrapment of poly(N-isopropylacrylamide) (PNIPAAm)-containing homopolymer and block copolymers. A previously developed approach based on using solutions of the polymeric modifier in a solvent which swells the base membrane polymer had been used, and conditions have been varied. One block copolymer of PNIPAAm with polybutylacrylate (PBA) had been selected as best suited modifier. Models related to the underlying deswelling/entrapment process which leads to fixation of the modifier have been considered. For PP membrane, characterization of pore size distribution in dry state revealed a significant decrease of pore size as a consequence of the entrapment modification. Surface properties have been analysed by ATR-FTIR spectroscopy and water contact angle measurements, which confirmed the presence of modifier and a strong improvement of surface and pore wettability. The thermo-sensitive properties of either outer surface and inner pore wall of modified PP membranes have been verified by temperature-dependence of captive bubble contact angle and water permeability, respectively, both due to hydratation/dehydratation and volume phase transition of PNIPAAm around the lower critical solution temperature (LCST) of the block copolymer PBA- b-PNIPAAm which was around 31-32. °C. The effects of protein desorption from the modified membrane where bovine serum albumin (BSA) had been previously adsorbed were studied by measuring water flux upon manipulating water temperature during water filtration cum washing. In addition, non-porous PP plates had been modified using the same procedure and all the surface characterization results showed similar modification efficiency and surface properties as for porous PP membranes, confirming the dominating role of entrapment of the amphiphilic functional macromolecules into the PP surface layer instead of simple deposition onto the surface. © 2011 Elsevier B.V.
view abstract doi: 10.1016/j.memsci.2011.02.018 2011 • 45 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 • 44 Structure and phase behavior of archaeal lipid monolayers
Jeworrek, C. and Evers, F. and Erlkamp, M. and Grobelny, S. and Tolan, M. and Chong, P.L.-G. and Winter, R.
Langmuir 27 13113-13121 (2011)We report X-ray reflectivity (XRR) and grazing incidence X-ray diffraction (GIXD) measurements of archaeal bipolar tetraether lipid monolayers at the air-water interface. Specifically, Langmuir films made of the polar lipid fraction E (PLFE) isolated from the thermoacidophilic archaeon Sulfolobus acidocaldarius grown at three different temperatures, i.e., 68, 76, and 81 °C, were examined. The dependence of the structure and packing properties of PLFE monolayers on surface pressure were analyzed in a temperature range between 10 and 50 °C at different pH values. Additionally, the interaction of PLFE monolayers (using lipids derived from cells grown at 76 °C) with the ion channel peptide gramicidin was investigated as a function of surface pressure. A total monolayer thickness of approximately 30 Å was found for all monolayers, hinting at a U-shaped conformation of the molecules with both head groups in contact with the interface. The monolayer thickness increased with rising film pressure and decreased with increasing temperature. At 10 and 20 °C, large, highly crystalline domains were observed by GIXD, whereas at higher temperatures no distinct crystallinity could be observed. For lipids derived from cells grown at higher temperatures, a slightly more rigid structure in the lipid dibiphytanyl chains was observed. A change in the pH of the subphase had an influence only on the structure of the lipid head groups. The addition of gramicidin to an PLFE monolayer led to a more disordered state as observed by XRR. In GIXD measurements, no major changes in lateral organization could be observed, except for a decrease of the size of crystalline domains, indicating that gramicidin resides mainly in the disordered areas of the monolayer and causes local membrane perturbation, only. © 2011 American Chemical Society.
view abstract doi: 10.1021/la202027s 2011 • 43 In vivo wear of a squeaky alumina-on-alumina hip prosthesis a case report
Laurent, M.P. and Pourzal, R. and Fischer, A. and Bertin, K.C. and Jacobs, J.J. and Wimmer, M.A.
Journal of Bone and Joint Surgery - Series A 93 e27 (2011)
doi: 10.2106/JBJS.I.00930 2011 • 42 Softening of PMMA brushes upon collapse/swelling transition. A combined neutron reflectivity and nanomechanical cantilever sensor study
Lenz, S. and Rühm, A. and Major, J. and Berger, R. and Gutmann, J.S.
Macromolecules 44 360-367 (2011)In this work, we establish a direct correlation between chain mechanics and structural properties of polymer brushes upon swelling. We present experimental results on poly(methyl methacrylate) (PMMA) brushes prepared via surface initiated atomic transfer radical polymerization. Neutron reflectivity studies gave insight into the brush thickness and volume fraction profiles of the brush, gradually swollen with solvent mixtures. Comparison of our experiments with scaling theory yielded specific polymer - solvent interaction parameters and gave insight into the desorption and adsorption behavior of bad and good solvents, respectively. Insight into the brush's chain mechanics was obtained from surface stress investigations using the nanomechanical cantilever sensor bending technique. It was shown that polymer brush swelling leads to a decrease in surface stress due to chain disentanglements and the related softening of the polymer brush under θ-solvent conditions. © 2010 American Chemical Society.
view abstract doi: 10.1021/ma1021715 2011 • 41 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 • 40 Simultaneous visualization of surface topography and concentration field by means of scanning electrochemical microscopy using a single electrochemical probe and impedance spectroscopy
Pähler, M. and Schuhmann, W. and Gratzl, M.
ChemPhysChem 12 2798-2805 (2011)Scanning electrochemical microscopy visualizes concentration profiles. To determine the location of the probe relative to topographical features of the substrate, knowledge of the probe-to-sample distance at each probe position is required. The use of electrochemical impedance spectroscopy for obtaining information on the substrate-to-probe distance and on the concentration of interest using the electrochemical probe alone is suggested. By tuning the frequencies of interrogation, the probe-to-substrate distance can be derived followed by interrogation of processes that carry information on concentration at lower frequencies. These processes may include charge-transfer relaxation, diffusional relaxation at the electrode, and open-circuit potential at zero frequency. A potentiometric chloride sensing microprobe is used herein to reconstruct both topography and the concentration field at a microscopic diffusional source of chloride. Electrochemical impedance spectroscopy is used for simultaneously obtaining information on the substrate-to-probe distance and on the concentration of Cl - ions. By tuning the frequencies of interrogation to fast migrational relaxations in the solution, the substrate-to-probe distance can be derived followed by interrogation of processes that carry information on concentration at lower frequencies (see picture). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/cphc.201100428 2011 • 39 Robust surface electronic properties of topological insulators: Bi 2 Te3 films grown by molecular beam epitaxy
Plucinski, L. and Mussler, G. and Krumrain, J. and Herdt, A. and Suga, S. and Grützmacher, D. and Schneider, C.M.
Applied Physics Letters 98 (2011)The surface electronic properties of the important topological insulator Bi2 Te3 are shown to be robust under an extended surface preparation procedure, which includes exposure to atmosphere and subsequent cleaning and recrystallization by an optimized in situ sputter-anneal procedure under ultrahigh vacuum conditions. Clear Dirac-cone features are displayed in high-resolution angle-resolved photoemission spectra from the resulting samples, indicating remarkable insensitivity of the topological surface state to cleaning-induced surface roughness. © 2011 American Institute of Physics.
view abstract doi: 10.1063/1.3595309 2011 • 38 Nanostructuring of titania thin films by a combination of microfluidics and block-copolymer-based sol-gel templating
Rawolle, M. and Ruderer, M.A. and Prams, S.M. and Zhong, Q. and Magerl, D. and Perlich, J. and Roth, S.V. and Lellig, P. and Gutmann, J.S. and Müller-Buschbaum, P.
Small 7 884-891 (2011)Sol-gel templating of titania thin films with the amphiphilic diblock copolymer poly(dimethyl siloxane)-block-methyl methacrylate poly(ethylene oxide) is combined with microfluidic technology to control the structure formation. Due to the laminar flow conditions in the microfluidic cell, a better control of the local composition of the reactive fluid is achieved. The resulting titania films exhibit mesopores and macropores, as determined with scanning electron microscopy, X-ray reflectivity, and grazing incidence small angle X-ray scattering. The titania morphology has three features that are beneficial for application in photovoltaics: 1) a large surface-to-volume ratio important for charge generation with disordered hexagonally arranged mesopores of 25 nm size and a film porosity of up to 0.79, 2) enhanced light scattering that enables the absorption of more light, and 3) a dense titania layer with a thickness of about 6 nm at the substrate (bottom electrode) to prevent short circuits. An optical characterization complements the structural investigation. Microfluidics and sol-gel templating are combined to design titania thin films with well defined structures. The obtained films consist of mesopores with a diameter of 25 nm and macropores, as seen with scanning electron microscopy and grazing incidence small angle X-ray scattering. This structure is interesting for potential applications in inorganic-organic photovoltaics because of the large surface area and enhanced light scattering as compared to structures templated without microfluidics. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/smll.201001734 2011 • 37 Electronic excitations induced by hydrogen surface chemical reactions on gold
Schindler, B. and Diesing, D. and Hasselbrink, E.
Journal of Chemical Physics 134 (2011)Associated with chemical reactions at surfaces energy may be dissipated exciting surface electronic degrees of freedom. These excitations are detected using metal-insulator-metal (MIM) heterostructures (Ta-TaOx-Au) and the reactions of H with and on a Au surface are probed. A current corresponding to 510-5 electrons per adsorbing H atom and a marked isotope effect are observed under steady-state conditions. Analysis of the current trace when the H atom flux is intermitted suggests that predominantly the recombination reaction creates electronic excitations. Biasing the front versus the back electrode of the MIM structure provides insights into the spectrum of electronic excitations. The observed spectra differ for the two isotopes H and D and are asymmetric when comparing negative and positive bias voltages. Modeling indicates that the excited electrons and the concurrently created holes differ in their energy distributions. © 2011 American Institute of Physics.
view abstract doi: 10.1063/1.3523647 2011 • 36 Supramolecular structures: Robust materials from weak forces
Nature Nanotechnology 6 136-137 (2011)
doi: 10.1038/nnano.2011.28 2011 • 35 Wetting morphologies and their transitions in grooved substrates
Seemann, R. and Brinkmann, M. and Herminghaus, S. and Khare, K. and Law, B.M. and McBride, S. and Kostourou, K. and Gurevich, E. and Bommer, S. and Herrmann, C. and Michler, D.
Journal of Physics Condensed Matter 23 (2011)When exposed to a partially wetting liquid, many natural and artificial surfaces equipped with complex topographies display a rich variety of liquid interfacial morphologies. In the present article, we focus on a few simple paradigmatic surface topographies and elaborate on the statics and dynamics of the resulting wetting morphologies. It is demonstrated that the spectrum of wetting morphologies increases with increasing complexity of the groove structure. On elastically deformable substrates, additional structures in the liquid morphologies can be observed, which are caused by deformations of the groove geometry in the presence of capillary forces. The emergence of certain liquid morphologies in grooves can be actively controlled by changes in wettability and geometry. For electrically conducting solid substrates, the apparent contact angle can be varied by electrowetting. This allows, depending on groove geometry, a reversible or irreversible transport of liquid along surface grooves. In the case of irreversible liquid transport in triangular grooves, the dynamics of the emerging instability is sensitive to the apparent hydrodynamic slip at the substrate. On elastic substrates, the geometry can be varied in a straightforward manner by stretching or relaxing the sample. The imbibition velocity in deformable grooves is significantly reduced compared to solid grooves, which is a result of the microscopic deformation of the elastic groove material close to the three phase contact line. © 2011 IOP Publishing Ltd.
view abstract doi: 10.1088/0953-8984/23/18/184108 2011 • 34 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 • 33 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 • 32 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 • 31 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 2010 • 30 A microelectrochemical sensing system for the determination of Epstein-Barr virus antibodies
Bandilla, M. and Zimdars, A. and Neugebauer, S. and Motz, M. and Schuhmann, W. and Hartwich, G.
Analytical and Bioanalytical Chemistry 398 2617-2623 (2010)An electrochemical method for the detection of Epstein-Barr virus (EBV) infections is described. The method relies on an immunoassay with electrochemical read-outs based on recombinant antigens. The antigens are immobilised on an Au electrode surface and used to complementarily bind antibodies from serum samples found during different stages of infection with EBV. Thiol chemistry under formation of self-assembled monolayers functions as a means to immobilise the antigens at the Au electrodes. A reporter system consisting of a secondary antibody labelled with alkaline phosphatase is used for electrochemical detection. The feasibility of the assay design is demonstrated and the assay performance is tested against the current gold standard in EBV detection. Close correlation is obtained for the results found for the developed electrochemical immunoassay and a standard line assay. Moreover, the electrochemical immunoassay is combined with a nanoporous electrode system allowing signal amplification by means of redox recycling. An amplification factor of 24 could be achieved. © Springer-Verlag 2010.
view abstract doi: 10.1007/s00216-010-3926-y 2010 • 29 Functional coatings for anti-biofouling applications by surface segregation of block copolymer additives
Berndt, E. and Behnke, S. and Dannehl, A. and Gajda, A. and Wingender, J. and Ulbricht, M.
Polymer 51 5910-5920 (2010)Temperature responsive or bactericidal coatings with poly(n-butyl methacrylate) (PBMA) as bulk material and surface segregated poly(n-butyl acrylate)- block-poly-(N-isopropylacrylamide) (PBA- b-PNIPAAm) or poly(n-butyl acrylate)- block-quaternized poly(2-(dimethylamino)ethyl methacrylate) (PBA- b-PDMAEMAq) as additive were prepared via sequential solvent evaporation of polymer solutions in a solvent mixture. The degree of enrichment at the air surface of the coating and the functionality were examined for different molecular weight additives with different block ratios obtained via Atom Transfer Radical Polymerization (ATRP). The design of the block copolymers with an anchor block (PBA) which is compatible with the bulk polymer (PBMA) and water-compatible functional blocks (PNIPAAm and PDMAEMAq) along with the selection of suited solvent mixtures based on pre-estimation of the selective solubility and sequential evaporation via the Hansen solubility parameters and vapor pressures, respectively, were found to work very well. A small fraction of water in the solvent mixture had been crucial to obtain surface segregation of the functional block, e.g., a PNIPAAm surface with temperature-switchable wettability. Reversible temperature dependent wettability and long term stability of the functionalization, based on contact angle data, were obtained for an optimized PBA- b-PNIPAAm additive. Surface charge density, estimated from dye binding and zeta potential measurements, and killing efficiency against Staphylococcus aureus were investigated for PBA- b-PDMAEMAq as additive. Both block copolymer additives were found to dominate the surface properties and the functionality of the PBMA coating. © 2010 Elsevier Ltd.
view abstract doi: 10.1016/j.polymer.2010.10.002 2010 • 28 Modified DLC-coated guide pads for BTA deep hole drilling tools
Biermann, D. and Kessler, N. and Upmeier, T. and Stucky, T.
Key Engineering Materials 438 195-202 (2010)The BTA (Boring and Trepanning Association) deep hole drilling process is commonly used to machine boreholes with a large drilling depth-to-diameter ratio (l/D) and outstanding workpiece quality. The asymmetric tool design leads to a nonzero radial component of the cutting force and the passive force, which are conducted to the borehole wall by so-called guide pads. These guide pads smooth the borehole wall by a forming process and improve the surface quality. Processes, that machine materials with a high adhesion tendency, such as high alloy stainless steel, suffer from poor surface quality in the borehole and the adhesion from the workpiece material on the guide pads. In this paper modified Diamond-Like-Carbon (DLC) coated guide pads for BTA deep hole drilling tools are investigated. The scope of the experiments was the reduction of the adhesion by reducing the friction coefficient of the guide pads, as well as the improvement of the quality of the borehole wall. © (2010) Trans Tech Publications.
view abstract doi: 10.4028/www.scientific.net/KEM.438.195 2010 • 27 Sol-gel deposition of multiply doped thermographic phosphor coatings Al2O3:(Cr3+, M3+) (M = Dy, Tm) for wide range surface temperature measurement application
Eckert, C. and Pflitsch, C. and Atakan, B.
Progress in Organic Coatings 68 126-129 (2010)A promising method of measuring surface temperatures in harsh environments is the use of thermographic phosphor coatings. There, the surface temperature is evaluated from the phosphorescence decay lifetime following a pulsed laser or flash lamp light excitation. Depending on the used dopant, single doped M3+:α-Al2O3 (M = Cr, Dy, Tm) emit at 694 nm (Cr3+), 488 nm (Dy3+), 584 nm (Dy3+), and 459 nm (Tm3+), respectively. However, the accessible temperature range with a single dopant is limited: for the Cr3+-transition from 293 K up to 900 K, and for the Dy3+ and Tm3+-transitions both from 1073 K up to 1473 K. In the present study a new approach is followed to extend these limitations by co-doping two dopants using the sol-gel method and dip coating of α-Al2O3 thin films. For that application (Dy3+ + Cr3+) co-doped thin α-Al2O3 films and (Tm3+ + Cr3+) co-doped α-Al2O3 films with thicknesses of 4-6 μm were prepared, and the temperature-dependent luminescence properties (emission spectra and lifetimes) were analysed after pulsed laser excitation in the UV (355 nm). The phosphorescence lifetime as a function of temperature were measured between 293 K and 1473 K. A considerably extended range for surface temperature evaluation was established following this new approach by combining different dopants on the molecular level. © 2009 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.porgcoat.2009.08.021 2010 • 26 Controlled orientation of DNA in a binary SAM as a key for the successful determination of DNA hybridization by means of electrochemical impedance spectroscopy
Gebala, M. and Schuhmann, W.
ChemPhysChem 11 2887-2895 (2010)Determination of DNA hybridization at electrode surfaces modified with thiol-tethered single-stranded DNA (ssDNA) capture probes and co-assembled with short-chain thiol derivatives using electrochemical impedance spectroscopy requires a careful design of the electrode/electrolyte interface as well as an in-depth understanding of the processes at the interface during DNA hybridization. The influence of the electrode potential, the ssDNA coverage, the ionic strength, the nature of the thiol derivative and especially the Debye length are shown to have a significant impact on the impedance spectra. A mixed monolayer comprising-in addition to the ssDNA capture probe-both mercaptohexanol (MCH) and mercaptopropionic acid (MPA) is suggested as an interface design which allows a high efficiency of the DNA hybridization concomitantly with a reliable modulation of the charge-transfer resistance of the electrode upon hybridization. © 2010 Wiley-VCH Verlag GmbH& Co. KGaA, Weinheim.
view abstract doi: 10.1002/cphc.201000210 2010 • 25 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 • 24 Modification of GaAs surface by low-current Townsend discharge
Gurevich, E.L. and Kittel, S. and Hergenröder, R. and Astrov, Y.A. and Portsel, L.M. and Lodygin, A.N. and Tolmachev, V.A. and Ankudinov, A.V.
Journal of Physics D: Applied Physics 43 (2010)The influence of stationary spatially homogeneous Townsend discharge on the (1 0 0) surface of semi-insulating GaAs samples is studied. Samples exposed to both electrons and ions in a nitrogen discharge at a current density j = 60 μA cm-2 are studied by means of x-ray photoelectron spectroscopy, ellipsometry and atomic force microscopy. It is shown that an exposure to low-energy ions (< 1 eV) changes the crystal structure of the semiconductor for a depth of up to 10-20 nm, although the stoichiometric composition does not change. The exposure to low-energy electrons (< 10 eV) forms an oxide layer, which is 5-10 nm thick. Atomic force microscopy demonstrates that the change in the surface potential of the samples may exceed 100 mV, for both discharge polarities, while the surface roughness does not increase. © 2010 IOP Publishing Ltd.
view abstract doi: 10.1088/0022-3727/43/27/275302 2010 • 23 Plasma mediated collagen-I-coating of metal implant materials to improve biocompatibility
Hauser, J. and Koeller, M. and Bensch, S. and Halfmann, H. and Awakowicz, P. and Steinau, H.-U. and Esenwein, S.
Journal of Biomedical Materials Research - Part A 94 19-26 (2010)This study describes the collagen-I coating of titanium and steel implants via cold low-pressure gas plasma treatment. To analyze the coatings in terms of biocompatibility osteoblast-like osteosarcoma cells and human leukocytes were cultivated on the metal surfaces. Two different implant materials were assessed (Ti6Al4V, X2CrNiMo18) and four different surface properties were evaluated: (a) plasma pretreated and collagen-I coated implant materials; (b) collagen-I dip-coated without plasma pretreatment; (c) plasma treated but not collagen-I coated; (d) standard implant materials served as control. The different coating characteristics were analyzed by scanning electron microscopy (SEM). For adhesion and viability tests calcein-AM staining of the cells and Alamar blue assays were performed. The quantitative analysis was conducted by computer assisted microfluorophotography and spectrometer measurements. SEM analysis revealed that stable collagen-I coatings could not be achieved on the dip-coated steel and titanium alloys. Only due to pretreatment with low-pressure gas plasma a robust deposition of collagen I on the surface could be achieved. The cell viability and cell attachment rate on the plasma pretreated, collagen coated surfaces was significantly (p < 0.017) increased compared to the non coated surfaces. Gas plasma treatment is a feasible method for the deposition of proteins on metal implant materials resulting in an improved biocompatibility in vitro. © 2010 Wiley Periodicals, Inc.
view abstract doi: 10.1002/jbm.a.32672 2010 • 22 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 • 21 The effect of radiation processing and filler morphology on the biomechanical stability of a thermoset polyester composite
Jayabalan, M. and Shalumon, K.T. and Mitha, M.K. and Ganesan, K. and Epple, M.
Biomedical Materials 5 (2010)The effect of radiation processing and filler morphology on the biodegradation and biomechanical stability of a poly(propylene fumarate)/hydroxyapatite composite was investigated. Radiation processing influenced both cross-linking and biodegradation of the composites. Irradiation with a dose of 3 Mrad resulted in enhanced cross-linking, mechanical properties and a higher storage modulus which are favourable for dimensional stability of the implant. The particle morphology of the added hydroxyapatite in the highly cross-linked state significantly influenced the biomechanical and interfacial stability of the composites. Reorganization of agglomerated hydroxyapatite occurred in the cross-linked polymeric matrix under dynamic mechanical loading under simulated physiological conditions. Such a reorganization may increase the damping characteristics of the composite. © 2010 IOP Publishing Ltd.
view abstract doi: 10.1088/1748-6041/5/2/025009 2010 • 20 Extrinsic screening of ferroelectric domains in Pb (Zr0.48 Ti0.52) O3
Krug, I. and Barrett, N. and Petraru, A. and Locatelli, A. and Mentes, T.O. and Niño, M.A. and Rahmanizadeh, K. and Bihlmayer, G. and Schneider, C.M.
Applied Physics Letters 97 (2010)The variation in the surface potential as a function of the ferroelectric polarization of micron scale domains in a thin epitaxial film of Pb (Zr 0.48 Ti0.52) O3 is measured using mirror electron microscopy. Domains were written using piezoforce microscopy. The surface potential for each polarization was deduced from the mirror to low energy electron microscopy transition in the local reflectivity curve. The effect of extrinsic screening of the fixed polarization charge at the ferroelectric surface is demonstrated. The results are compared with density functional theory calculations. © 2010 American Institute of Physics.
view abstract doi: 10.1063/1.3523359 2010 • 19 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 • 18 Nitrogen-doped carbon nanotubes as a cathode catalyst for the oxygen reduction reaction in alkaline medium
Nagaiah, T.C. and Kundu, S. and Bron, M. and Muhler, M. and Schuhmann, W.
Electrochemistry Communications 12 338-341 (2010)A new approach to synthesize nitrogen-doped carbon nanotubes (NCNTs) as catalysts for oxygen reduction by treating oxidized CNTs with ammonia is presented. The surface properties and oxygen reduction activities were characterized by cyclic voltammetry, rotating disk electrode and X-ray photoelectron spectroscopy. NCNTs treated at 800 °C show improved electrocatalytic activity for oxygen reduction as compared with commercially available Pt/C catalysts. © 2009 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.elecom.2009.12.021 2010 • 17 Sol-gel-deposition of thin TiO2:Eu3+ thermographic phosphor films
Nebatti, A. and Pflitsch, C. and Eckert, C. and Atakan, B.
Progress in Organic Coatings 68 146-150 (2010)A relatively new promising method for surface temperature measurement is the use of thermographic phosphors. For this application, the temperature-dependent luminescence properties of europium(III)-doped anatase (TiO2:Eu3+) thin films were studied. The films were prepared by the sol-gel method using dip coating. The structures and the morphology of the films were determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Electron dispersive X-ray spectroscopy (EDX) was used to verify the europium concentration within the films. For using the films as temperature sensors the optical properties are the main concern. Therefore, the emission spectra of the films were measured after ultraviolet laser excitation (355 nm). They indicate that the red characteristic emission (617 nm) of TiO2:Eu3+ due to the 5D0 →7F2 electric dipole transition is the strongest. The decay time constant of the exponential emission decay under UV excitation with a Nd:YAG laser (355 nm, f = 10 Hz) is strongly temperature dependent in the range from 200 °C up to 400 °C, making it useful for temperature evaluation. The temperature dependence was measured for the emission line at 617 nm; the results demonstrate that anatase doped europium(III) can be used as a thermographic phosphor. © 2009 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.porgcoat.2009.08.024 2010 • 16 Carbon-stabilized mesoporous MoS2 - Structural and surface characterization with spectroscopic and catalytic tools
Polyakov, M. and Poisot, M. and Van Den Berg, M.W.E. and Drescher, T. and Lotnyk, A. and Kienle, L. and Bensch, W. and Muhler, M. and Grünert, W.
Catalysis Communications 12 231-237 (2010)Structural and surface properties of carbon-containing mesoporous MoS 2 and of a reference MoS2 were studied with various techniques including XRD, elemental analysis, TEM, XPS, EXAFS, nitrogen physisorption, oxygen chemisorption (OCS), determination of exchangeable surface hydrogen, and kinetic study of test reactions like ethene hydrogenation and H2/D2 exchange. The study was made before and after use of these catalysts in the hydrodesulfurization of dibenzothiophene. The microstructure of carbon-stabilized MoS2 is characterized by nanoslabs of 2 nm average stacking height embedded in an amorphous matrix with a very broad pore-size distribution. Thermal stress induced a collapse of the microporous structure leading to the formation of mainly mesopores. The carbon is well-distributed over the bulk, without any signature of carbide species detected neither in XPS nor in EXAFS measurements. The activity patterns of both materials (related to the OCS capacity) were similar despite the differing sulfur content, with the carbon-stabilized MoS2 being more sulfur deficient. This suggests that the catalytic properties of the latter material were caused by near-stoichiometric MoS2 apparently present in the nanoslabs, whereas the sulfur vacancies in the sulfur-deficient amorphous phase were blocked by strongly adsorbed carbon residues. Interestingly, the HDS reaction did not cause significant changes of the properties of the carbon-stabilized MoS2. Conversely, the reference MoS2 was strongly activated, in particular with respect to ethene hydrogenation, which can be explained by a pronounced sulfur loss during the HDS reaction, without significant site blockage by the coke deposited. © 2010 Elsevier B.V. All rights reserved.
view abstract doi: 10.1016/j.catcom.2010.09.011 2010 • 15 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 • 14 Elimination of Biological Contaminations from Surfaces by Plasma Discharges: Chemical Sputtering
Rauscher, H. and Kylian, O. and Benedikt, J. and von Keudell, A. and Rossi, F.
Chemphyschem 11 1382--1389 (2010)Plasma treatment of surfaces as a sterilisation or decontamination method is a promising approach to overcome limitations of conventional techniques. The precise characterisation of the employed plasma discharges, the application of sensitive surface diagnostic methods and targeted experiments to separate the effects of different agents, have led to rapid progress in the understanding of different relevant elementary processes. This contribution provides an overview of the most relevant and recent results, which reveal the importance of chemical sputtering as one of the most important processes for the elimination of biological residuals. Selected studies on the interaction of plasmas with bacteria, proteins and polypeptides are highlighted, and investigations employing beams of atoms and ions confirming the prominent role of chemical sputtering are presented. With this knowledge, it is possible to optimize the plasma treatment for decontamination/sterilisation purposes in terms of discharge composition, density of active species and UV radiation intensity.
view abstract doi: 10.1002/cphc.200900757 2010 • 13 Hydrogen vibrational modes on graphene and relaxation of the C-H stretch excitation from first-principles calculations
Sakong, S. and Kratzer, P.
Journal of Chemical Physics 133 (2010)Density functional theory (DFT) calculations are used to determine the vibrational modes of hydrogen adsorbed on graphene in the low-coverage limit. Both the calculated adsorption energy of a H atom of 0.8 eV and calculated C-H stretch vibrational frequency of 2552 cm-1 are unusually low for hydrocarbons, but in agreement with data from electron energy loss spectroscopy on hydrogenated graphite. The clustering of two adsorbed H atoms observed in scanning tunneling microscopy images shows its fingerprint also in our calculated spectra. The energetically preferred adsorption on different sublattices correlates with a blueshift of the C-H stretch vibrational modes in H adatom clusters. The C-H bending modes are calculated to be in the 1100 cm-1 range, resonant with the graphene phonons. Moreover, we use our previously developed methods to calculate the relaxation of the C-H stretch mode via vibration-phonon interaction, using the Born-Oppenheimer surface for all local modes as obtained from the DFT calculations. The total decay rate of the H stretch into other H vibrations, thereby creating or annihilating one graphene phonon, is determined from Fermi's golden rule. Our calculations using the matrix elements derived from DFT calculations show that the lifetime of the H stretch mode on graphene is only several picoseconds, much shorter than on other semiconductor surfaces such as Ge(001) and Si(001). © 2010 American Institute of Physics.
view abstract doi: 10.1063/1.3474806 2010 • 12 Micro- and nanopatterning of functional organic monolayers on oxide-free silicon by laser-induced photothermal desorption
Scheres, L. and Klingebiel, B. and Ter Maat, J. and Giesbers, M. and De Jong, H. and Hartmann, N. and Zuilhof, H.
Small 6 1918-1926 (2010)The photothermal laser patterning of functional organic monolayers, prepared on oxide-free hydrogen-terminated silicon, and subsequent backfi lling of the laser-written lines with a second organic monolayer that differs in its terminal functionality, is described. Since the thermal monolayer decomposition process is highly nonlinear in the applied laser power density, subwavelength patterning of the organic monolayers is feasible. After photothermal laser patterning of hexadecenyl monolayers, the lines freed up by the laser are backfi lled with functional acid fl uoride monolayers. Coupling of cysteamine to the acid fl uoride groups and subsequent attachment of Au nanoparticles allows easy characterization of the functional lines by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Depending on the laser power and writing speed, functional lines with widths between 1.1 μm and 250 nm can be created. In addition, trifl uoroethyl-terminated (TFE) monolayers are also patterned. Subsequently, the decomposed lines are backfi lled with a nonfunctional hexadecenyl monolayer, the TFE stripes are converted into thiol stripes, and then finally covered with Au nanoparticles. By reducing the lateral distance between the laser lines, Au-nanoparticle stripes with widths close to 100 nm are obtained. Finally, in view of the great potential of this type of monolayer in the fi eld of biosensing, the ease of fabricating biofunctional patterns is demonstrated by covalent binding of fl uorescently labeled oligo-DNA to acidfl uoride-backfi lled laser lines, which-as shown by fl uorescence microscopy-is accessible for hybridization.Copyright © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/smll.201000189 2010 • 11 Synthesis of glass-coated SERS nanoparticle probes via SAMs with terminal SiO2 precursors
Schütz, M. and Küstner, B. and Bauer, M. and Schmuck, C. and Schlücker, S.
Small 6 733-737 (2010)A short synthesis route to silica-encapsulated nanoparticles coated with a self-assembled monolayer (SAM) is presented. The organic molecules within the SAM contain a SiO2 precursor to render the surface vitreophilic. Due to the high mechanical and chemical stability of a glass shell, such particles can be used as probes in targeted research with surface-enhanced Raman scattering as the read-out method. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/smll.200902065 2010 • 10 Dissociation of oxygen on Ag(100) induced by inelastic electron tunneling
Sprodowski, C. and Mehlhorn, M. and Morgenstern, K.
Journal of Physics Condensed Matter 22 (2010)Scanning tunneling microscopy (STM) is used to study the dissociation of molecular oxygen on Ag(100) induced by inelastic electron tunneling (IET) at 5 K. This dissociation is possible above 3.3 V with a yield of (3.63 ± 0.47) × 10-9 per electron. Dissociation leads to three different types of hot atom motion: lateral motion, a cannon ball mechanism, and abstractive dissociation. Analysis of the I -t characteristics during dissociation suggests that the dissociation is proceeded by an adsorption site change. © 2010 IOP Publishing Ltd.
view abstract doi: 10.1088/0953-8984/22/26/264005 2010 • 9 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 • 8 Effect of surface charge distribution on the adsorption orientation of proteins to lipid monolayers
Tiemeyer, S. and Paulus, M. and Tolan, M.
Langmuir 26 14064-14067 (2010)The adsorption orientation of the proteins lysozyme and ribonuclease A (RNase A) to a neutral 1,2-dipalmitoyl-snglycero- 3-phosphocholine (DPPC) and a negatively charged stearic acid lipid film was investigated by means of X-ray reflectivity. Both proteins adsorbed to the negatively charged lipid monolayer, whereas at the neutral monolayer, no adsorption was observed. For acquiring comprehensive information on the proteins' adsorption, X-ray reflectivity data were combined with electron densities obtained from crystallographic data. With this method, it is possible to determine the orientation of adsorbed proteins in solution underneath lipid monolayers. While RNase A specifically coupled with its positively charged active site to the negatively charged lipid monolayer, lysozyme prefers an orientation with its long axis parallel to the Langmuir film. In comparison to the electrostatic maps of the proteins, our results can be explained by the discriminative surface charge distribution of lysozyme and RNase A. © 2010 American Chemical Society.
view abstract doi: 10.1021/la102616h 2010 • 7 Desirability-based multi-criteria optimization of HVOF spray experiments to manufacture fine structured wear-resistant 75Cr 3C 2-25(NiCr20) coatings
Tillmann, W. and Vogli, E. and Baumann, I. and Kopp, G. and Weihs, C.
Journal of Thermal Spray Technology 19 392-408 (2010)Thermal spraying of fine feedstock powders allow the deposition of cermet coatings with significantly improved characteristics and is currently of great interest in science and industry. However, due to the high surface to volume ratio and the low specific weight, fine particles are not only difficult to spray but also show a poor flowability in the feeding process. In order to process fine powders reliably and to preserve the fine structure of the feedstock material in the final coating morphology, the use of novel thermal spray equipment as well as a thorough selection and optimization of the process parameters are fundamentally required. In this study, HVOF spray experiments have been conducted to manufacture fine structured, wear-resistant cermet coatings using fine 75Cr 3C 2-25(Ni20Cr) powders (-8 + 2 μm). Statistical design of experiments (DOE) has been utilized to identify the most relevant process parameters with their linear, quadratic and interaction effects using Plackett-Burman, Fractional-Factorial and Central Composite designs to model the deposition efficiency of the process and the majorly important coating properties: roughness, hardness and porosity. The concept of desirability functions and the desirability index have been applied to combine these response variables in order to find a process parameter combination that yields either optimum results for all responses, or at least the best possible compromise. Verification experiments in the so found optimum obtained very satisfying or even excellent results. The coatings featured an average microhardness of 1004 HV 0.1, a roughness Ra = 1.9 μm and a porosity of 1.7%. In addition, a high deposition efficiency of 71% could be obtained. © 2009 ASM International.
view abstract doi: 10.1007/s11666-009-9383-5 2010 • 6 The influence of surface composition of nanoparticles on their interactions with serum albumin
Treuel, L. and Malissek, M. and Gebauer, J.S. and Zellner, R.
ChemPhysChem 11 3093-3099 (2010)Interactions between differently functionalised silver and gold nanoparticles (NPs) as well as polystyrene nanoparticles with bovine serum albumin (BSA) are studied using circular dichroism (CD) spectroscopy. It is found that the addition of NPs to the protein solution destroys part of the helical secondary structure of the protein as a result of surface adsorption. From the loss of free protein and hence the extent of their structural change adsorption equilibrium constants are derived. The results reveal that citrate-coated gold and silver NPs exhibit much stronger interactions with BSA than polymeric or polymer-coated metallic NPs. It is therefore concluded that for the particles considered, the influence of surface composition on the interaction behaviour dominates that of the core. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/cphc.201000174 2010 • 5 Co-adsorption processes, kinetics and quantum mechanical modelling of nanofilm semiconductor gas sensors
Velasco-Vélez, J.-J. and Kunze, U. and Haas, T. and Doll, T.
Physica Status Solidi (A) Applications and Materials Science 207 924-929 (2010)A quantum mechanical model of co-adsorption on semiconductor surfaces is developed and successfully adopted towards exposure to several gases. It is related to nanofilms and thus allows the application of electric fields altering the electronic surface properties of adsorption centres (electroadsorptive effect, EAE). The model is matched against experimental data with O 2, NO 2 and CO measurements under the hypothesis of no direct interaction among the species. However the sequence of adsorption plays an important role where the adsorption of one gas species is opening up other sites that are filled by another sort of impinging molecules. Quantum mechanical modelling of co-adsorption: (a) NO 2 and CO present at the SnO 2 surface. (b) Simplified model. (c) Probability of adsorption. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract doi: 10.1002/pssa.200983322 2010 • 4 Reversible and noncompetitive inhibition of β-tryptase by protein surface binding of tetravalent peptide ligands identified from a combinatorial split-mix library
Wich, P.R. and Schmuck, C.
Angewandte Chemie - International Edition 49 4113-4116 (2010)(Figure Presented) Molecular plug: On-bead screening of a combinatorial library of 216 tetravalent oligopeptides reveals highly specific, noncompetitive inhibitors of the serine protease β-tryptase with nanomolar affinity. The ligands most likely bind to the protein surface and act as a molecular plug that blocks access to the active sites, which are buried inside a central cavity (see picture). © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.
view abstract doi: 10.1002/anie.200907221 2010 • 3 Wear mechanisms in metal-on-metal bearings: The importance of tribochemical reaction layers
Wimmer, M.A. and Fischer, A. and Büscher, R. and Pourzal, R. and Sprecher, C. and Hauert, R. and Jacobs, J.J.
Journal of Orthopaedic Research 28 436-443 (2010)Metal-on-metal (MoM) bearings are at the forefront in hip resurfacing arthroplasty. Because of their good wear characteristics and design flexibility, MoM bearings are gaining wider acceptance with market share reaching nearly 10% worldwide. However, concerns remain regarding potential detrimental effects of metal particulates and ion release. Growing evidence is emerging that the local cell response is related to the amount of debris generated by these bearing couples. Thus, an urgent clinical need exists to delineate the mechanisms of debris generation to further reduce wear and its adverse effects. In this study, we investigated the microstructural and chemical composition of the tribochemical reaction layers forming at the contacting surfaces of metallic bearings during sliding motion. Using X-ray photoelectron spectroscopy and transmission electron microscopy with coupled energy dispersive X-ray and electron energy loss spectroscopy, we found that the tribolayers are nanocrystalline in structure, and that they incorporate organic material stemming from the synovial fluid. This process, which has been termed "mechanical mixing," changes the bearing surface of the uppermost 50 to 200 nm from pure metallic to an organic composite material. It hinders direct metal contact (thus preventing adhesion) and limits wear. This novel finding of a mechanically mixed zone of nanocrystalline metal and organic constituents provides the basis for understanding particle release and may help in identifying new strategies to reduce MoM wear. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.
view abstract doi: 10.1002/jor.21020 2010 • 2 Anti-nonspecific protein adsorption properties of biomimetic glycocalyx-like glycopolymer layers: Effects of glycopolymer chain density and protein size
Yang, Q. and Kaul, C. and Ulbricht, M.
Langmuir 26 5746-5752 (2010)In many cases, biomaterials surfaces are desired to be resistant to protein adsorption. A system fulfilling this task in nature is the so-called glycocalyx. The glycocalyx is an outer layer on the cell membrane with bound glycoproteins and glycolipids, exposing a pattern of carbohydrate groups. There is a growing interest to mimic this glycocalyx layer to have a tool to overcome the problems with uncontrolled protein adsorption on biomaterials. In this work a glycocalyx-like layer is artificially imitated by surface-initiated atom transfer radical polymerization (ATRP) of a glycomonomer, d-gluconamidoethyl methacrylate (GAMA), from a mixed self-assembled monolayer (SAM) of an ATRP initiator-immobilized hydroxyl-terminated thiol and a methyl-terminated thiol as diluent. Fourier transform infrared spectroscopy (FT/IR-ATR), contact angle, and ellipsometry measurements were employed to confirm the grafting of the glycopolymer. The anti-nonspecific protein binding properties of this glycopolymer layer were then investigated with surface plasmon resonance (SPR). Three proteins with different size, lysozyme, bovine serum albumin (BSA), and fibrinogen were used as model solutes to investigate the influence of protein size on the protein resistance behavior. The glycopolymer chain density was controlled during surface-initiated ATRP by varying the ratio of the components in the mixed SAM, and the chain length was adjusted by ATRP time. The effect of chain density in combination with the protein size was also evaluated. The most important results are that poly(GAMA) layers of higher grafting density show resistance to adsorption of the model proteins used in this work and that the amount of adsorbed protein depends on the length and density of the glycopolymer chains and also on the size of the proteins. © 2010 American Chemical Society.
view abstract doi: 10.1021/la903895q 2010 • 1 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