Scientific Output

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 • 275 Development of a 3D Printing Technique for PVDF Thin Films for Sensor Elements of Electronic Devices
    Dubkov, S.V. and Silibin, M.V. and Lebedev, S.V. and Ryazanov, R.I. and Shvartsman, V.V.
    Proceedings of the 2020 IEEE Conference of Russian Young Researchers in Electrical and Electronic Engineering, EIConRus 2020 2587-2590 (2020)
    The paper proposes a method for forming thin films of polyvinylidene fluoride using a 3D printer. The extrusion parameters of a filament based on PVDF with a diameter of 1.75 were established and the optimal characteristics for printing by 3D printer were selected (nozzle temperature, table temperature, feed rate). Studies have shown that the local polarization of a thin PVDF film is stable for 20 hours. © 2020 IEEE.
    view abstractdoi: 10.1109/EIConRus49466.2020.9039127
  • 2020 • 274 Comparative study of the residual stress development in HMDSN-based organosilicon and silicon oxide coatings
    Jaritz, M. and Hopmann, C. and Wilski, S. and Kleines, L. and Banko, L. and Grochla, D. and Ludwig, Al. and Dahlmann, R.
    Journal of Physics D: Applied Physics 53 (2020)
    To investigate the stress formation mechanisms in thin plasma polymers, a comparative study of organosilicon (SiNOCH) and silicon oxide (SiOx) coatings in dependence of power input for deposition was conducted. Both coating types were produced in a low-pressure (15 Pa) microwave excited hexamethyldilisazane (HMDSN) plasma. Residual stress values were obtained using a high-throughput, time resolved and in-situ measurement method, including a CCD-camera, a line laser and micro-machined cantilever sensor chips. Both plasma polymer types were shown to form residual stresses with opposite signs. The stress evolution in the coatings revealed a strong dependency on the variation of power input for deposition. The SiOx coating exhibits mostly compressive stresses. Higher power inputs constitute higher ion momentums as well as a higher degree of fragmentation of the monomer. The SiOx coatings were deposited with a high oxygen flow and with a higher average energy of the plasma for all investigated parameter sets than the SiNOCH coating. Therefore, it is conceivable that ion peening is mostly responsible for the compressive stress formation in the SiOx coatings. In contrast to the SiOx coating, the SiNOCH coating can be applied without residual stress. For higher excitation powers, tensile stresses are predominant, most likely due to attractive forces between island or column boundaries and crosslinking. © 2020 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6463/ab8ceb
  • 2020 • 273 Synthesis of Novel Sulfobetaine Polymers with Differing Dipole Orientations in Their Side Chains, and Their Effects on the Antifouling Properties
    Schönemann, E. and Koc, J. and Aldred, N. and Clare, A.S. and Laschewsky, A. and Rosenhahn, A. and Wischerhoff, E.
    Macromolecular Rapid Communications 41 (2020)
    The impact of the orientation of zwitterionic groups, with respect to the polymer backbone, on the antifouling performance of thin hydrogel films made of polyzwitterions is explored. In an extension of the recent discussion about differences in the behavior of polymeric phosphatidylcholines and choline phosphates, a quasi-isomeric set of three poly(sulfobetaine methacrylate)s is designed for this purpose. The design is based on the established monomer 3-[N-2-(methacryloyloxy)ethyl-N,N-dimethyl]ammonio-propane-1-sulfonate and two novel sulfobetaine methacrylates, in which the positions of the cationic and the ionic groups relative to the polymerizable group, and thus also to the polymer backbone, are altered. The effect of the varied segmental dipole orientation on their water solubility, wetting behavior by water, and fouling resistance is compared. As model systems, the adsorption of the model proteins bovine serum albumin (BSA), fibrinogen, and lysozyme onto films of the various polyzwitterion surfaces is studied, as well as the settlement of a diatom (Navicula perminuta) and barnacle cyprids (Balanus improvisus) as representatives of typical marine fouling communities. The results demonstrate the important role of the zwitterionic group's orientation on the polymer behavior and fouling resistance. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/marc.201900447
  • 2020 • 272 Optimization and quality evaluation of the interlayer bonding performance of additively manufactured polymer structures
    Striemann, P. and Hülsbusch, D. and Niedermeier, M. and Walther, F.
    Polymers 12 (2020)
    The application of additive manufacturing changes from prototypes to series production. In order to fulfill all requirements of series production, the process and the material characteristics must be known. The machine operator of additive manufacturing systems is both a component and a material producer. Nevertheless, there is no standardized procedure for the manufacturing or testing of such materials. This includes the high degree of anisotropy of additively manufactured polymers via material extrusion. The interlayer bonding performance between two layers in the manufacturing direction z is the obvious weakness that needs to be improved. By optimizing this interlayer contact zone, the overall performance of the additively manufactured polymer is increased. This was achieved by process modification with an infrared preheating system (IPS) to keep the temperature of the interlayer contact zone above the glass transition temperature during the manufacturing process. Combining destructive and non-destructive testing methods, the process modification IPS was determined and evaluated by a systematic approach for characterizing the interlayer bonding performance. Thereby, tensile tests under quasi-static and cyclic loading were carried out on short carbon flber-reinforced polyamide (SCFRP). In addition, micro-computed tomography and microscopic investigations were used to determine the process quality. The IPS increases the ultimate inter layer tensile strength by approx. 15% and shows at end encyto significantly improved the fatigue properties. Simultaneously, the analysis of the micro-computed tomography data shows a homogenization of the void distribution by using the IPS. © 2020 by the authors.
    view abstractdoi: 10.3390/POLYM12051166
  • 2020 • 271 Mode-locked diode laser-based two-photon polymerisation
    Surkamp, N. and Zyla, G. and Gurevich, E.L. and Klehr, A. and Knigge, A. and Ostendorf, A. and Hofmann, M.R.
    Electronics Letters 56 91-93 (2020)
    In this Letter, the authors present the construction of three-dimensional microstructures by two-photon polymerisation induced by ultrashort pulses of a mode-locked diode laser. The ultrafast light source is based on a diode laser with segmented metallisation to realise a waveguide integrated saturable absorber. It is subsequently amplified and compressed resulting in ultrashort laser pulses of 440 fs length and average output power of 160 mW at a fundamental repetition rate of 383.1 MHz. These pulses are coupled into a customised two-photon polymerisation setup. A series of suspended lines were fabricated between support cuboids for testing the process behaviour. A 3D structure with complex features was polymerised to demonstrate the high potential for mode-locked diode lasers in the field of direct laser writing. © The Institution of Engineering and Technology 2020.
    view abstractdoi: 10.1049/el.2019.2385
  • 2020 • 270 Electroenzymatic CO2 Fixation Using Redox Polymer/Enzyme-Modified Gas Diffusion Electrodes
    Szczesny, J. and Ruff, A. and Oliveira, A.R. and Pita, M. and Pereira, I.A.C. and De Lacey, A.L. and Schuhmann, W.
    ACS Energy Letters 5 321-327 (2020)
    We describe the fabrication of gas diffusion electrodes modified with polymer/enzyme layers for electroenzymatic CO2 fixation. For this, a metal-free organic low-potential viologen-modified polymer has been synthesized that reveals a redox potential of around-0.39 V vs SHE and is thus able to electrically wire W-dependent formate dehydrogenase from Desulfovibrio vulgaris Hildenborough, which reversibly catalyzes the conversion of CO2 to formate. The use of gas diffusion electrodes eliminates limitations arising from slow mass transport when solid carbonate is used as CO2 source. The electrodes showed satisfactory stability that allowed for their long-term electrolysis application for electroenzymatic formate production. Copyright © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acsenergylett.9b02436
  • 2020 • 269 Multiple character of non-monotonic size-dependence for relaxation dynamics in polymer-particle and binary mixtures
    Zirdehi, E.M. and Voigtmann, T. and Varnik, F.
    Journal of Physics Condensed Matter 32 (2020)
    Adding plasticizers is a well-known procedure to reduce the glass transition temperature in polymers. It has been recently shown that this effect shows a non-monotonic dependence on the size of additive molecules (2019 J. Chem. Phys. 150 024903). In this work, we demonstrate that, as the size of the additive molecules is changed at fixed concentration, multiple extrema emerge in the dependence of the system's relaxation time on the size ratio. The effect occurs on all relevant length scales including single monomer dynamics, decay of Rouse modes and relaxation of the chain's end-to-end vector. A qualitatively similar trend is found within mode-coupling theoretical results for a binary hard-sphere mixture. An interpretation of the effect in terms of local packing efficiency and coupling between the dynamics of minority and majority species is provided. © 2020 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-648X/ab757c
  • 2019 • 268 Printing "smart" Inks of Redox-Responsive Organometallic Polymers on Microelectrode Arrays for Molecular Sensing
    Cirelli, M. and Hao, J. and Bor, T.C. and Duvigneau, J. and Benson, N. and Akkerman, R. and Hempenius, M.A. and Vancso, G.J.
    ACS Applied Materials and Interfaces 11 37060-37068 (2019)
    Printing arrays of responsive spots for multiplexed sensing with electrochemical readout requires new molecules and precise, high-throughput deposition of active compounds on microelectrodes with spatial control. We have designed and developed new redox-responsive polymers, featuring a poly(ferrocenylsilane) (PFS) backbone and side groups with disulfide units, which allow an efficient and stable bonding to Au substrates, using sulfur-gold coupling chemistry in a "grafting-to" approach. The polymer molecules can be employed for area selective molecular sensing following their deposition by high-precision inkjet printing. The new PFS derivatives, which serve as "molecular inks", were characterized by 1H NMR, 13C NMR, and FTIR spectroscopies and by gel permeation chromatography. The viscosity and surface tension of the inks were assessed by rheology and pendant drop contact angle measurements, respectively. Commercial microelectrode arrays were modified with the new PFS ink by using inkjet printing in the "drop-on-demand" mode. FTIR spectroscopy, AFM, and EDX-SEM confirmed a successful, spatially localized PFS modification of the individual electrodes within the sensing cells of the microelectrode arrays. The potential application of these devices to act as an electrochemical sensor array was demonstrated with a model analyte, ascorbic acid, by using cyclic voltammetry and amperometric measurements. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acsami.9b11927
  • 2019 • 267 Thin plasma polymerised coatings for corrosion protection against strong alkaline solutions
    Jaritz, M. and Hopmann, C. and Wilski, S. and Kleines, L. and Rudolph, M. and Awakowicz, P. and Dahlmann, R.
    Surface and Coatings Technology 374 232-241 (2019)
    Thin plasma polymers were applied on gold- and aluminium substrates using low pressure microwave- and radiofrequency-excited hexamethyldisilazane (HMDSN) plasma. The corrosion resistance properties of these coatings against sodium hydroxide solution (NaOH) was characterised by means of time resolved electrochemical impedance spectroscopy (EIS) and light microscopy. The evaluated resistance values were correlated with coating topography, chemical composition, wetting properties, and morphology with particular focus on porosity. Coating porosity was determined by using cyclic voltammetry (CV) and light microscopy. The topography and chemistry of the coatings were characterised by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The wetting properties were determined by optical contact angle (OCA) measurements. It is shown that the plasma polymer's resistance against NaOH can be greatly increased by lowering the energy input during the deposition process. This can be attributed to the strong correlation between porosity and resistivity: low energy input during plasma deposition leads to the formation of smaller and more uniform particles in the plasma bulk and possibly a Stranski–Krastanov growth of the layers, resulting in a smoother coating topography and lower nano-porosity. A more dense and compact coating morphology leads to a better corrosion protection performance. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2019.05.069
  • 2019 • 266 Functionalization of Ultrafiltration Membranes for Integration of Specific Adsorber Properties [Funktionalisierung von Ultrafiltrationsmembranen zur Integration von spezifischen Adsorbereigenschaften]
    Koch, D. and Ulbricht, M.
    Chemie-Ingenieur-Technik 91 1129-1134 (2019)
    By integrating a water-soluble polymer, which has the ability to complex heavy metal ions into ultrafiltration membranes, the separation process could be enhanced to enable also filtration of these species. In this work, a membrane and an adsorber polymer were functionalized with complementary reactive groups so that the adsorber polymer could be immobilized in the porous support layer of the ultrafiltration membrane via click reaction. The separation performances and membrane characteristics of the synthesized membranes are comparable to those of conventional UF membranes. © 2019, Wiley-VCH Verlag. All rights reserved.
    view abstractdoi: 10.1002/cite.201900046
  • 2019 • 265 Time and Mechanism of Nanoparticle Functionalization by Macromolecular Ligands during Pulsed Laser Ablation in Liquids
    Letzel, A. and Reich, S. and Dos Santos Rolo, T. and Kanitz, A. and Hoppius, J. and Rack, A. and Olbinado, M.P. and Ostendorf, A. and Gökce, B. and Plech, A. and Barcikowski, S.
    Langmuir 35 3038-3047 (2019)
    Laser ablation of gold in liquids with nanosecond laser pulses in aqueous solutions of inorganic electrolytes and macromolecular ligands for gold nanoparticle size quenching is probed inside the laser-induced cavitation bubble by in situ X-ray multicontrast imaging with a Hartmann mask (XHI). It is found that (i) the in situ size quenching power of sodium chloride (NaCl) in comparison to the ablation in pure water can be observed by the scattering contrast from XHI already inside the cavitation bubble, while (ii) for polyvinylpyrrolidone (PVP) as a macromolecular model ligand an in situ size quenching cannot be observed. Complementary ex situ characterization confirms the overall size quenching ability of both additive types NaCl and PVP. The macromolecular ligand as well as its monomer N-vinylpyrrolidone (NVP) are mainly effective for growth quenching of larger nanoparticles on later time scales, leading to the conclusion of an alternative interaction mechanism with ablated nanoparticles compared to the electrolyte NaCl, probably outside of the cavitation bubble, in the surrounding liquid phase. While monomer and polymer have similar effects on the particle properties, with the polymer being slightly more efficient, only the polymer is effective against hydrodynamic aggregation. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.8b01585
  • 2019 • 264 Ultrathin Films of 2D Hofmann-Type Coordination Polymers: Influence of Pillaring Linkers on Structural Flexibility and Vertical Charge Transport
    Rubio-Giménez, V. and Escorcia-Ariza, G. and Bartual-Murgui, C. and Sternemann, C. and Galbiati, M. and Castells-Gil, J. and Real, J.A. and Tatay, S. and Martí-Gastaldo, C.
    Chemistry of Materials 31 7277-7287 (2019)
    Searching for novel materials and controlling their nanostructuration into electronic devices is a challenging task ahead of chemists and chemical engineers. Even more so when this new application requires an exquisite control over the morphology, crystallinity, roughness, and orientation of the films produced. In this context, it is of critical importance to analyze the influence of the chemical composition of perspective materials on their properties at the nanoscale. We report the fabrication of ultrathin films (thickness < 30 nm) of a family of FeII Hofmann-like coordination polymers (CPs) by using an optimized liquid-phase epitaxy (LPE) set up. The series [Fe(L)2{Pt(CN)4}] (L = pyridine, pyrimidine, and isoquinoline) conform an ideal platform for correlating the effect of the axial nitrogenated ligand with changes to their structural response to guests or electrical resistance. All film properties relevant to device integration have been thoroughly analyzed with complementary surface techniques for a meaningful comparison. Our results reveal that changes to this ligand can hinder the structural transformation triggered by the absorption of guest molecules previously reported for the pyridine phase. Also important, it can substantially hinder vertical charge transport across the layers, even at the ultrathin film limit. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acs.chemmater.9b01634
  • 2019 • 263 Thermo-/moisture-responsive shape-memory effect of poly(2-ethyl-2-oxazoline) networks
    Segiet, D. and Raidt, T. and Özdem, H. and Weckes, S. and Tiller, J.C. and Katzenberg, F.
    Journal of Polymer Science, Part B: Polymer Physics 57 1053-1061 (2019)
    In this work, poly(2-ethyl-2-oxazoline) (PEtOx) is crosslinked to realize a moisture- and thermo-responsive shape-memory polymer. The obtained PEtOx networks exhibit excellent shape-memory properties with storable strains of up to 650% and recovery values of 100% over at least 10 shape-memory cycles. The trigger temperature (Ttrig) of 68 °C of a PEtOx network at a relative humidity (RH) of 0% decreases with increasing moisture and equals room temperature at an RH of 40%. Thus, programmed PEtOx networks trigger sensitively on a certain temperature/moisture combination and, further, can be programmed as well as triggered at room temperature exclusively by varying humidity. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1053–1061. © 2019 Wiley Periodicals, Inc.
    view abstractdoi: 10.1002/polb.24859
  • 2019 • 262 Quasi-static characterization of polyamide-based discontinuous CFRP manufactured by additive manufacturing and injection molding
    Striemann, P. and Hülsbusch, D. and Niedermeier, M. and Walther, F.
    Key Engineering Materials 809 KEM 386-391 (2019)
    Generating serial components via additive manufacturing (AM) a deep understanding of process-related characteristics is necessary. The extrusion-based AM called fused layer manufacturing (FLM), also known as fused deposition modeling (FDM™) or fused filament fabrication (FFF) is an AM process for producing serial components. Improving mechanical properties of AM parts is done by adding fibers in the raw material to reinforce the polymer. The study aims to create a more detailed comprehension of FLM and process-related characteristics with their influence on the composite. Thereby, a short carbon fiber-reinforced polyamide (CarbonX™ Nylon, 3DXTECH, USA) with 12.5 wt.-% fiber content, 7 μm fiber diameter, and 150 to 400 µm fiber length distribution was investigated. To separate process-related characteristics of FLM, reference specimens were fabricated via injection molding (IM) with single-batch material. For the mechanical characterization, quasi-static tensile tests were carried out in accordance to DIN 527-2. Quality assessment including void content and void distribution was performed via micro-computed tomography (CT). The mechanical characterization clarifies effects on mechanical properties depending on process-related characteristics of FLM. CT scans show higher void contents of FLM specimens compared to IM specimens and void orientation dependent on printing direction. FLM shows process-related characteristics which generally strengthen mechanical properties of polymers. Nevertheless, tensile strength of FLM specimens decrease by more than 28% compared to quasi-homogenous IM specimens. © 2019 Trans Tech Publications Ltd, Switzerland.
    view abstractdoi: 10.4028/
  • 2019 • 261 Nonfouling textiles with tunable antimicrobial activity based on a zwitterionic polyamine finish
    Timma, L.M. and Lewald, L. and Gier, F. and Homey, L. and Neyer, C. and Nickisch-Hartfiel, A. and Gutmann, J.S. and Oberthür, M.
    RSC Advances 9 9783-9791 (2019)
    Antimicrobial finishes for textiles and other surfaces that act without the release of biocides to the environment (contact biocides) or by inhibiting microbial adhesion (antifouling action) are viewed as promising and environmentally friendly alternatives to current products. We have used polyvinylamine polymers that were functionalized with zwitterionic sulfobetaine side chains with different degrees of substitution (DS) for the finishing of poly(ethylene terephthalate) (PET) and cotton fabrics in a water-based pad-dry-cure process. After washing with different surfactants, a stable finish with total polymer add-ons of 0.2-0.5 wt% was achieved. The finished textiles efficiently inhibited the adhesion of proteins and bacteria to the surface even with a small DS as low as 20%. Textiles finished with polymers with a low DS also showed significant antibacterial activity, most notably against Staphylococcus aureus. Accordingly, textile finishes with either pure antiadhesive (DS > 50%) or combined antiadhesive and antibacterial properties (DS = 20-50%) are accessible using this approach. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/C8RA09975H
  • 2019 • 260 A light-driven Nernstian biosupercapacitor
    Zhao, F. and Bobrowski, T. and Ruff, A. and Hartmann, V. and Nowaczyk, M.M. and Rögner, M. and Conzuelo, F. and Schuhmann, W.
    Electrochimica Acta 306 660-666 (2019)
    Following inspiration by natural photosynthesis, the design and fabrication of semi-artificial biophotoelectrochemical devices able to harvest solar energy and aiming on the implementation of green and sustainable energy conversion systems is presently an important field of research. Here we present the development of a fully light-driven biosupercapacitor fabricated by incorporation of isolated photosystem 2 and photosystem 1 protein complexes embedded within the same Os-complex modified redox polymer. By this, light energy is stored at both electrodes within the polymer-based pseudocapacitive matrix in the form of Os 3+ centers at the photosystem1-based biocathode and in the form of Os 2+ centers at the photosystem 2-based bioanode. The stored energy can be released on demand into bursts of electricity. Due to the purely light-driven self-charging process, the biosupercapacitor provided a power output of 1.0 μW cm −2 after 200 s charging time. Moreover, the use of different electrode materials and their implication on the performance of the implemented biodevice is evaluated. © 2019 Elsevier Ltd
    view abstractdoi: 10.1016/j.electacta.2019.03.168
  • 2018 • 259 Communication: Correlation of terminal relaxation rate and viscosity enhancement in supramolecular small-molecule liquids
    Bierwirth, S.P. and Gainaru, C. and Böhmer, R.
    Journal of Chemical Physics 148 (2018)
    Monohydroxy alcohols with a large supramolecular Debye-type dielectric process often exhibit a significant decoupling between the Debye mode and the structural relaxation. Using shear rheology, a technique that is sensitive to both processes as well, the current work reveals a widely applicable correlation in terms of the dynamical onset and the viscosity enhancement of the supramolecular shear mode with respect to the structural relaxation. Rheological data from an array of about 50 oligomers, associating polymers, (polymerized) ionic liquids, and aqueous solutions corroborate this correlation which thus appears to be generic to many classes of complex fluids. © 2018 Author(s).
    view abstractdoi: 10.1063/1.5037803
  • 2018 • 258 The Open Circuit Voltage in Biofuel Cells: Nernstian Shift in Pseudocapacitive Electrodes
    Conzuelo, F. and Marković, N. and Ruff, A. and Schuhmann, W.
    Angewandte Chemie - International Edition 57 13681-13685 (2018)
    In the development of biofuel cells great effort is dedicated to achieving outstanding figures of merit, such as high stability, maximum power output, and a large open circuit voltage. Biofuel cells with immobilized redox mediators, such as redox polymers with integrated enzymes, show experimentally a substantially higher open circuit voltage than the thermodynamically expected value. Although this phenomenon is widely reported in the literature, there is no comprehensive understanding of the potential shift, the high open circuit voltages have not been discussed in detail, and hence they are only accepted as an inherent property of the investigated systems. We demonstrate that this effect is the result of a Nernstian shift of the electrode potential when catalytic conversion takes place in the absence or at very low current flow. Experimental evidence confirms that the immobilization of redox centers on the electrode surface results in the assembled biofuel cell delivering a higher power output because of charge storage upon catalytic conversion. Our findings have direct implications for the design and evaluation of (bio)fuel cells with pseudocapacitive elements. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/anie.201808450
  • 2018 • 257 Glycerol Oxidation Using MgO- and Al2O3-supported Gold and Gold–Palladium Nanoparticles Prepared in the Absence of Polymer Stabilizers
    Dodekatos, G. and Abis, L. and Freakley, S.J. and Tüysüz, H. and Hutchings, G.J.
    ChemCatChem 10 1351-1359 (2018)
    Au and AuPd nanoparticles supported on MgO and Al2O3 were employed for the selective aqueous phase oxidation of glycerol under basic conditions. Catalysts were prepared by sol-immobilization without the addition of a stabilizing agent such as polyvinyl alcohol (PVA), which is generally added to stabilize the noble metal sol prior to immobilization. The obtained materials prepared with and without stabilizing agent were active for glycerol oxidation and showed similar catalytic performances—implying that the stabilizing polymer is not required to obtain active materials. Depending on the support used, it was possible to tailor the selectivity towards the desired oxidation products by using catalysts prepared with or without stabilizing agent. PVA-free Au/γ-Al2O3 exhibited a remarkably high selectivity towards tartronic acid (40 % at 97 % conversion), which was not observed for Au/γ-Al2O3 prepared with PVA (27 % at isoconversion). Selective glycerol oxidation performed under base-free conditions over AuPd/MgO catalysts also corroborated the previous results that the presence of a stabilizing polymer is not required to prepare active catalysts by sol-immobilization. Thus, a facile way to circumvent the inherent drawbacks encountered by the use of polymer stabilizers during catalyst preparation is presented herein. Experimental results suggest that the presence of the polymer stabilizers can affect the reaction pathways and control selectivity. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/cctc.201800074
  • 2018 • 256 Coil-coated steel sheets measured by DMA using an immersion testing cell
    Haakmann, F. and Mayer, C. and Raulf, M.
    Journal of Thermal Analysis and Calorimetry (2018)
    The effect of humidity on the glass transition temperature of coatings is well known and analyzed. In this study, an analysis method is introduced for analyzing coil-coated metal sheets submerged in water and water/methyl ethyl ketone (MEK) by using an immersion cell coupled to a DMA. For this purpose, a model polyurethane acrylate coating was applied to zinc/magnesium-coated steel plates and measured before and after immersion in water and water/MEK by DMA and immersion cell. The results show a shift of glass transition temperature from 138 to 13 °C of the coating by storing the coated steel plates under water and immersion testing. A time-dependent diffusion of water from the cell into the coating until saturation can be observed. An increasing concentration of MEK within the immersion cell results in a greater shift of the glass transition temperature. Overall, the immersion cell seems to be a useful tool for in situ characterization of the behavior of coil coating varnishes in liquid environment (Foster et al. in Prog Organ Coat 51:244–249, 2004, van der Wel et al. in Prog Organ Coat 37:1–14, 1999). © 2018, Akadémiai Kiadó, Budapest, Hungary.
    view abstractdoi: 10.1007/s10973-018-7944-x
  • 2018 • 255 Entropically driven Polymeric Enzyme Inhibitors by End-Group directed Conjugation
    Hijazi, M. and Krumm, C. and Cinar, S. and Arns, L. and Alachraf, W. and Hiller, W. and Schrader, W. and Winter, R. and Tiller, J.C.
    Chemistry - A European Journal 24 4523-4527 (2018)
    A new generic concept for polymeric enzyme inhibitors is presented using the example of poly(2-methyl-2-oxazoline) (PMOx) terminated with an iminodiacetate (IDA) function. These polymers are shown to be non-competitive inhibitors for horseradish peroxidase (HRP). Mechanistic investigations revealed that the polymer is directed to the protein by its end group and collapses at the surface in an entropy-driven process as shown by isothermal titration calorimetry. The dissociation constant of the complex was determined as the inhibition constant Ki using HRP kinetic activity measurements. Additional experiments suggest that the polymer does not form a diffusion layer around the protein, but might inhibit by inducing minor conformational changes in the protein. This kind of inhibitor offers new avenues towards designing bioactive compounds. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/chem.201800168
  • 2018 • 254 Bioelectrocatalytic and electrochemical cascade for phosphate sensing with up to 6 electrons per analyte molecule
    Kopiec, G. and Starzec, K. and Kochana, J. and Kinnunen-Skidmore, T.P. and Schuhmann, W. and Campbell, W.H. and Ruff, A. and Plumeré, N.
    Biosensors and Bioelectronics 117 501-507 (2018)
    Despite the availability of numerous electroanalytical methods for phosphate quantification, practical implementation in point-of-use sensing remains virtually nonexistent because of interferences from sample matrices or from atmospheric O2. In this work, phosphate determination is achieved by the purine nucleoside phosphorylase (PNP) catalyzed reaction of inosine and phosphate to produce hypoxanthine which is subsequently oxidized by xanthine oxidase (XOx), first to xanthine and then to uric acid. Both PNP and XOx are integrated in a redox active Os-complex modified polymer, which not only acts as supporting matrix for the bienzymatic system but also shuttles electrons from the hypoxanthine oxidation reaction to the electrode. The bienzymatic cascade in this second generation phosphate biosensor selectively delivers four electrons for each phosphate molecule present. We introduced an additional electrochemical process involving uric acid oxidation at the underlying electrode. This further enhances the anodic current (signal amplification) by two additional electrons per analyte molecule which mitigates the influence of electrochemical interferences from the sample matrix. Moreover, while the XOx catalyzed reaction is sensitive to O2, the uric acid production and therefore the delivery of electrons through the subsequent electrochemical process are independent of the presence of O2. Consequently, the electrochemical process counterbalances the O2 interferences, especially at low phosphate concentrations. Importantly, the electrochemical uric acid oxidation specifically reports on phosphate concentration since it originates from the product of the bienzymatic reactions. These advantageous properties make this bioelectrochemical-electrochemical cascade particularly promising for point-of-use phosphate measurements. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.bios.2018.06.047
  • 2018 • 253 Comparison between the optical properties of injection molded and additive manufactured components
    Kuehn, C. and Mehl, O. and Laumer, T. and Witt, G.
    Procedia CIRP 74 259-263 (2018)
    Fused Layer Manufacturing (FLM) is an additive technology based on polymer material extrusion. Due to variations in temperature during the manufacturing process and the resulting stress between the stacked layers, the final parts show anisotropic mechanical properties. One possible approach for their reduction is the immediate local preheating of the surface via laser radiation. At first, our research examines the influence of laser parameters as wavelength, power, velocity and area of impact for the preheating of the surface. In addition, an overview of possible parameter combinations is given based on the selection of raw materials, its colors, thicknesses and the manufacturing process. Initially, the absorption level of the materials regarding the emitted wavelength is detected using a spectrophotometer. Subsequently, preheating tests are conducted with different laser types while the temperature is determined by a thermal camera. The selected laser type is planned to get mounted on a prototype-machine for further in-situ preheating experiments on FLM parts during the manufacturing process. © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.
    view abstractdoi: 10.1016/j.procir.2018.08.106
  • 2018 • 252 Formation of Polymeric Particles by Direct Polymerization on the Surface of a Supramolecular Template
    Li, M. and Zellermann, E. and Schmuck, C.
    Chemistry - A European Journal 24 9061-9065 (2018)
    Formation of polymeric materials on the surface of supramolecular assemblies is rather challenging because of the often weak noncovalent interactions between the self-assembled template and the monomers before polymerization. We herein show that the introduction of a supramolecular anion recognition motif, the guanidiniocarbonyl pyrrole cation (GCP), into a short Fmoc-dipeptide 1 leads to self-assembled spherical nanoparticles in aqueous solution. Negatively charged diacetylene monomers can be attached onto the surface of these nanoparticles, which, after UV polymerization, leads to the formation of a polymer shell around the self-assembled template. The hybrid supramolecular and polymeric nanoparticles demonstrate intriguing thermal hysteresis phenomena. The template nanoparticles could be disassembled upon treatment with organic base, which cleaved the Fmoc moiety on 1. This strategy thus showed that a supramolecular anion recognition motif allows the post-assembly formation of polymeric nanomaterials from anionic monomers around a cationic self-assembled template. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/chem.201705209
  • 2018 • 251 Comparative study on the deposition of silicon oxide permeation barrier coatings for polymers using hexamethyldisilazane (HMDSN) and hexamethyldisiloxane (HMDSO)
    Mitschker, F. and Schücke, L. and Hoppe, C. and Jaritz, M. and Dahlmann, R. and De Los Arcos, T. and Hopmann, C. and Grundmeier, G. and Awakowicz, P.
    Journal of Physics D: Applied Physics 51 (2018)
    The effect of the selection of hexamethyldisiloxane (HMDSO) and hexamethyldisilazane (HMDSN) as a precursor in a microwave driven low pressure plasma on the deposition of silicon oxide barrier coatings and silicon based organic interlayers on polyethylene terephthalate (PET) and polypropylene (PP) substrates is investigated. Mass spectrometry is used to quantify the absolute gas density and the degree of depletion of neutral precursor molecules under variation of oxygen admixture. On average, HMDSN shows a smaller density, a higher depletion and the production of smaller fragments. Subsequently, this is correlated with barrier performance and chemical structure as a function of barrier layer thickness and oxygen admixture on PET. For this purpose, the oxygen transmission rate (OTR) is measured and Fourier transformed infrared (FTIR) spectroscopy as well as x-ray photoelectron spectroscopy (XPS) is performed. HMDSN based coatings exhibit significantly higher barrier performances for high admixtures of oxygen (200 sccm). In comparison to HMDSO based processes, however, a higher supply of oxygen is necessary to achieve a sufficient degree of oxidation, cross-linking and, therefore, barrier performance. FTIR and XPS reveal a distinct carbon content for low oxygen admixtures (10 and 20 sccm) in case of HMDSN based coatings. The variation of interlayer thickness also reveals significantly higher OTR for HMDSO based coatings on PET and PP. Barrier performance of HMDSO based coatings improves with increasing interlayer thickness up to 10 nm for PET and PP. HMDSN based coatings exhibit a minimum of OTR without interlayer on PP and for 2 nm interlayer thickness on PET. Furthermore, HMDSN based coatings show distinctly higher bond strengths to the PP substrate. © 2018 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6463/aac0ab
  • 2018 • 250 Influence of average ion energy and atomic oxygen flux per Si atom on the formation of silicon oxide permeation barrier coatings on PET
    Mitschker, F. and Wißing, J. and Hoppe, C. and De Los Arcos, T. and Grundmeier, G. and Awakowicz, P.
    Journal of Physics D: Applied Physics 51 (2018)
    The respective effect of average incorporated ion energy and impinging atomic oxygen flux on the deposition of silicon oxide (SiOx) barrier coatings for polymers is studied in a microwave driven low pressure discharge with additional variable RF bias. Under consideration of plasma parameters, bias voltage, film density, chemical composition and particle fluxes, both are determined relative to the effective flux of Si atoms contributing to film growth. Subsequently, a correlation with barrier performance and chemical structure is achieved by measuring the oxygen transmission rate (OTR) and by performing x-ray photoelectron spectroscopy. It is observed that an increase in incorporated energy to 160 eV per deposited Si atom result in an enhanced cross-linking of the SiOx network and, therefore, an improved barrier performance by almost two orders of magnitude. Furthermore, independently increasing the number of oxygen atoms to 10 500 per deposited Si atom also lead to a comparable barrier improvement by an enhanced cross-linking. © 2018 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6463/aab1dd
  • 2018 • 249 A fully protected hydrogenase/polymer-based bioanode for high-performance hydrogen/glucose biofuel cells
    Ruff, A. and Szczesny, J. and Marković, N. and Conzuelo, F. and Zacarias, S. and Pereira, I.A.C. and Lubitz, W. and Schuhmann, W.
    Nature Communications 9 (2018)
    Hydrogenases with Ni- and/or Fe-based active sites are highly active hydrogen oxidation catalysts with activities similar to those of noble metal catalysts. However, the activity is connected to a sensitivity towards high-potential deactivation and oxygen damage. Here we report a fully protected polymer multilayer/hydrogenase-based bioanode in which the sensitive hydrogen oxidation catalyst is protected from high-potential deactivation and from oxygen damage by using a polymer multilayer architecture. The active catalyst is embedded in a low-potential polymer (protection from high-potential deactivation) and covered with a polymer-supported bienzymatic oxygen removal system. In contrast to previously reported polymer-based protection systems, the proposed strategy fully decouples the hydrogenase reaction form the protection process. Incorporation of the bioanode into a hydrogen/glucose biofuel cell provides a benchmark open circuit voltage of 1.15 V and power densities of up to 530 µW cm−2 at 0.85 V. © 2018, The Author(s).
    view abstractdoi: 10.1038/s41467-018-06106-3
  • 2018 • 248 Light-scattering data of protein and polymer solutions: A new approach for model validation and parameter estimation
    Voges, M. and Herhut, M. and Held, C. and Brandenbusch, C.
    Fluid Phase Equilibria 465 65-72 (2018)
    The development of separation processes for polymers or proteins from aqueous solutions requires a high amount of experimental effort, including phase-equilibrium data such as solid-liquid, liquid-liquid or vapor-liquid equilibria. This effort can be reduced by means of thermodynamic models. This work presents a new method for parameter estimation and validation of thermodynamic models by means of static-light-scattering (SLS) measurements. In this work the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) was used to predict directly the SLS data (Rayleigh ratio) of macromolecular solutions. In a first step, SLS data were measured for binary water/polyethylene glycol (PEG molecular weight ranging from 2000 to 12000 g/mol) mixtures and for binary water/lysozyme mixtures. Applying pure-component PC-SAFT parameters from literature, the SLS data of these binary mixtures were successfully predicted with PC-SAFT. In a second step, one binary interaction parameter between lysozyme and PEG was adjusted to new experimental SLS data of buffered PEG/lysozyme/water solutions with PEG6000 concentration of 20 g/L. Finally, SLS data for buffered ternary PEG/lysozyme/water solutions with PEG of different molecular weights (2000–12000 g/mol) and different concentrations (1–50 g/L) were accurately predicted with PC-SAFT. Thus, (1) the proposed approach allows predicting SLS data, and (2) the method provides an access to the estimation of model parameters by means of experimental SLS data, which are accessible with much less effort than experimental phase-equilibrium data. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.fluid.2018.02.022
  • 2018 • 247 Polymer Diffusion in the Interphase between Surface and Solution
    Weger, L. and Weidmann, M. and Ali, W. and Hildebrandt, M. and Gutmann, J.S. and Hoffmann-Jacobsen, K.
    Langmuir 34 7021-7027 (2018)
    Total internal reflection fluorescence correlation spectroscopy (TIR-FCS) is applied to study the self-diffusion of poly(ethylene glycol) solutions in the presence of weakly attractive interfaces. Glass coverslips modified with aminopropyl- and propyl-terminated silanes are used to study the influence of solid surfaces on polymer diffusion. A model of three phases of polymer diffusion allows to describe the experimental fluorescence autocorrelation functions. Besides the two-dimensional diffusion of adsorbed polymer on the substrate and three-dimensional free diffusion in bulk solution, a third diffusion time scale is observed with intermediate diffusion times. This retarded three-dimensional diffusion in the solution is assigned to the long-range effects of solid surfaces on diffusional dynamics of polymers. The respective diffusion constants show Rouse scaling (D ∼ N-1), indicating a screening of hydrodynamic interactions by the presence of the surface. Hence, the presented TIR-FCS method proves to be a valuable tool to investigate the effect of surfaces on polymer diffusion beyond the first adsorbed polymer layer on the 100 nm length scale. © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.8b00660
  • 2017 • 246 Reducing the efficiency-stability-cost gap of organic photovoltaics with highly efficient and stable small molecule acceptor ternary solar cells
    Baran, D. and Ashraf, R.S. and Hanifi, D.A. and Abdelsamie, M. and Gasparini, N. and Röhr, J.A. and Holliday, S. and Wadsworth, A. and Lockett, S. and Neophytou, M. and Emmott, C.J.M. and Nelson, J. and Brabec, C.J. and Amassian,...
    Nature Materials 16 363-369 (2017)
    Technological deployment of organic photovoltaic modules requires improvements in device light-conversion efficiency and stability while keeping material costs low. Here we demonstrate highly efficient and stable solar cells using a ternary approach, wherein two non-fullerene acceptors are combined with both a scalable and affordable donor polymer, poly(3-hexylthiophene) (P3HT), and a high-efficiency, low-bandgap polymer in a single-layer bulk-heterojunction device. The addition of a strongly absorbing small molecule acceptor into a P3HT-based non-fullerene blend increases the device efficiency up to 7.7 ± 0.1% without any solvent additives. The improvement is assigned to changes in microstructure that reduce charge recombination and increase the photovoltage, and to improved light harvesting across the visible region. The stability of P3HT-based devices in ambient conditions is also significantly improved relative to polymer:fullerene devices. Combined with a low-bandgap donor polymer (PBDTTT-EFT, also known as PCE10), the two mixed acceptors also lead to solar cells with 11.0 ± 0.4% efficiency and a high open-circuit voltage of 1.03 ± 0.01 V. © 2016 Nature Publishing Group
    view abstractdoi: 10.1038/nmat4797
  • 2017 • 245 Polybenzoxazine-Derived N-doped Carbon as Matrix for Powder-Based Electrocatalysts
    Barwe, S. and Andronescu, C. and Masa, J. and Ventosa, E. and Klink, S. and Genç, A. and Arbiol, J. and Schuhmann, W.
    ChemSusChem 10 2653-2659 (2017)
    In addition to catalytic activity, intrinsic stability, tight immobilization on a suitable electrode surface, and sufficient electronic conductivity are fundamental prerequisites for the long-term operation of particle- and especially powder-based electrocatalysts. We present a novel approach to concurrently address these challenges by using the unique properties of polybenzoxazine (pBO) polymers, namely near-zero shrinkage and high residual-char yield even after pyrolysis at high temperatures. Pyrolysis of a nanocubic prussian blue analogue precursor (KmMnx[Co(CN)6]y⋅n H2O) embedded in a bisphenol A and aniline-based pBO led to the formation of a N-doped carbon matrix modified with MnxCoyOz nanocubes. The obtained electrocatalyst exhibits high efficiency toward the oxygen evolution reaction (OER) and more importantly a stable performance for at least 65 h. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/cssc.201700593
  • 2017 • 244 Synthesis and Optical Characterization of Hybrid Organic-Inorganic Heterofluorene Polymers
    Fell, V.H.K. and Mikosch, A. and Steppert, A.-K. and Ogieglo, W. and Senol, E. and Canneson, D. and Bayer, M. and Schoenebeck, F. and Greilich, A. and Kuehne, A.J.C.
    Macromolecules 50 2338-2343 (2017)
    We synthesize heterofluorene monomers with Si, Ge, N, As, Se, and Te occupying the 9-position of the fluorene motif, which are then polymerized by Suzuki coupling. The optical properties of the obtained polymers are investigated in their solid state. We compare and elucidate effects in the materials absorption, emission, quantum yield (π), and fluorescence lifetime. Moreover, we determine the refractive indices n and absorption coefficient k by variable angle spectroscopic ellipsometry (VASE). We show that in addition to already known C, Si, and N containing polyfluorenes also Ge and As containing polymers exhibit amplified spontaneous emission. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.macromol.6b02611
  • 2017 • 243 Simple-liquid dynamics emerging in the mechanical shear spectra of poly(propylene glycol)
    Gainaru, C. and Hecksher, T. and Fan, F. and Xing, K. and Cetinkaya, B. and Olsen, N.B. and Dyre, J.C. and Sokolov, A.P. and Böhmer, R.
    Colloid and Polymer Science 295 2433-2437 (2017)
    The present dielectric investigations of methyl-terminated poly(propylene glycol) (PPG) oligomers reveal that near the glass transition the normal modes and segmental relaxation merge in a single-process susceptibility spectrum, similar to previous observations on OH-terminated species. Moreover, the present shear-mechanical measurements demonstrate that the vanishing of chain modes can be monitored without recourse to dielectric investigations, which are able to access chain dynamics only for the relatively small fraction of type A polymers. As the normal and segmental modes merge, the viscosity displays a crossover from a polymer-like regime governed by the chain dynamics, to a simple-liquid regime governed by the structural relaxation. © 2017 Springer-Verlag GmbH Germany
    view abstractdoi: 10.1007/s00396-017-4206-6
  • 2017 • 242 High-Affinity Copolymers Inhibit Digestive Enzymes by Surface Recognition
    Gilles, P. and Wenck, K. and Stratmann, I. and Kirsch, M. and Smolin, D.A. and Schaller, T. and De Groot, H. and Kraft, A. and Schrader, T.
    Biomacromolecules 18 1772-1784 (2017)
    This account presents a general method for the construction of polymeric surface binders for digestion enzymes. Two prominent parts, namely, the modification of the copolymer composition and the screening assay for the most powerful inhibitors are both amenable to parallelization. The concept hinges on the appropriate selection of amino-acid-selective comonomers, their free radical copolymerization, and subsequent screening of the resulting copolymer library for efficient enzyme inhibition. A microscale synthetic procedure for the copolymerization process was developed, which produces water-soluble affinity polymers that can be stored for years at room temperature. Initial parallel screening was conducted in standard enzyme assays to identify polymeric inhibitors, which were subsequently subjected to determination of IC50 values for their target enzyme. For all digestion enzymes, except elastase, a number of polymer inhibitors were found, some of which were selective toward one or two protein targets. Since the key monomers of the best inhibitors bind to amino acid residues in the direct vicinity of the active site, we conclude that efficient coverage of the immediate environment by the copolymers is critical. Strong interference with enzymatic activity is brought about by blocking the substrate access and product exit to and from the active site. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.biomac.7b00162
  • 2017 • 241 Experimental and analytical investigation of the force requirements in shear cutting of metal-polymer-metal composites
    Groche, P. and Übelacker, D. and Stein, P. and Steinbach, F. and Erman Tekkaya, A.
    International Journal of Material Forming 1-12 (2017)
    The increasing demand for lightweight design requires the use of multi materials such as metal-polymer-metal composites. These so-called sandwich panels offer a good stiffness-to-weight ratio. Production technologies like shear cutting have to be adapted for these materials. For a targeted adaption, a comprehensive knowledge about the cutting phases of the shear cutting process of sandwich panels is essential. Therefore, within this paper, the shear cutting process of sandwich panels is studied in detail. The conducted experimental studies indicate that the shear cutting process can be divided into five stages. Based on these findings, a new analytic model is introduced to predict the force displacement curves of sandwich panels. The quality of the new model is proven by comparison with existing analytic models for monolithic materials as well as with the experimental data. © 2017 Springer-Verlag France
    view abstractdoi: 10.1007/s12289-017-1343-x
  • 2017 • 240 Adsorption of finite semiflexible polymers and their loop and tail distributions
    Kampmann, T.A. and Kierfeld, J.
    Journal of Chemical Physics 147 (2017)
    We discuss the adsorption of semiflexible polymers to a planar attractive wall and focus on the questions of the adsorption threshold for polymers of finite length and their loop and tail distributions using both Monte Carlo simulations and analytical arguments. For the adsorption threshold, we find three regimes: (i) a flexible or Gaussian regime if the persistence length is smaller than the adsorption potential range, (ii) a semiflexible regime if the persistence length is larger than the potential range, and (iii) for finite polymers, a novel crossover to a rigid rod regime if the deflection length exceeds the contour length. In the flexible and semiflexible regimes, finite size corrections arise because the correlation length exceeds the contour length. In the rigid rod regime, however, it is essential how the global orientational or translational degrees of freedom are restricted by grafting or confinement. We discuss finite size corrections for polymers grafted to the adsorbing surface and for polymers confined by a second (parallel) hard wall. Based on these results, we obtain a method to analyze adsorption data for finite semiflexible polymers such as filamentous actin. For the loop and tail distributions, we find power laws with an exponential decay on length scales exceeding the correlation length. We derive and confirm the loop and tail power law exponents for flexible and semiflexible polymers. This allows us to explain that, close to the transition, semiflexible polymers have significantly smaller loops and both flexible and semiflexible polymers desorb by expanding their tail length. The tail distribution allows us to extract the free energy per length of adsorption for actin filaments from experimental data [D. Welch et al., Soft Matter 11, 7507 (2015)]. © 2017 Author(s).
    view abstractdoi: 10.1063/1.4990418
  • 2017 • 239 Polymer conformations in ionic microgels in the presence of salt: Theoretical and mesoscale simulation results
    Kobayashi, H. and Halver, R. and Sutmann, G. and Winkler, R.G.
    Polymers 9 (2017)
    We investigate the conformational properties of polymers in ionic microgels in the presence of salt ions by molecular dynamics simulations and analytical theory. A microgel particle consists of coarse-grained linear polymers, which are tetra-functionally crosslinked. Counterions and salt ions are taken into account explicitly, and charge-charge interactions are described by the Coulomb potential. By varying the charge interaction strength and salt concentration, we characterize the swelling of the polyelectrolytes and the charge distribution. In particular, we determine the amount of trapped mobile charges inside the microgel and the Debye screening length. Moreover, we analyze the polymer extension theoretically in terms of the tension blob model taking into account counterions and salt ions implicitly by the Debye-Hückel model. Our studies reveal a strong dependence of the amount of ions absorbed in the interior of the microgel on the electrostatic interaction strength, which is related to the degree of the gel swelling. This implies a dependence of the inverse Debye screening length k on the ion concentration; we find a power-law increase of k with the Coulomb interaction strength with the exponent 3/5 for a salt-free microgel and an exponent 1/2 for moderate salt concentrations. Additionally, the radial dependence of polymer conformations and ion distributions is addressed. © 2017 by the authors.
    view abstractdoi: 10.3390/polym9010015
  • 2017 • 238 Highly active and selective telechelic antimicrobial poly(2-oxazoline) copolymers
    Krumm, C. and Hijazi, M. and Trump, S. and Saal, S. and Richter, L. and Noschmann, G.G.F.K. and Nguyen, T.-D. and Preslikoska, K. and Moll, T. and Tiller, J.C.
    Polymer (United Kingdom) 118 107-115 (2017)
    The satellite group effect (SG) of telechelic antimicrobial polymers allows to increase or diminish the antimicrobial activity of the biocidal dodecyltrimethylammonium (DDA) group at the terminal of poly(2-methyl-2-oxazoline). Such polymers show good antimicrobial activities with MIC values as low as 10 μg mL−1 against the pathogenic bacterium Staphylococcus aureus and moderate selectivity with respect to blood cells (HC50/MIC: 10–120). Here, we show that the systematic variation of the nature and structure of the polymer backbone of such macromolecules results in biocidal polymers that rank among the highest antimicrobial activity against Staphylococcus aureus (MICS.aureus = 1–1.6 μg mL−1) and the best blood cell compatibilities (HC50/MICS.aureus = 1500–1700) known for amphiphilic antimicrobial polymers. Further, the polymers show a very high selectivity for Gram-positive bacteria (MICE.coli./MICS.aureus up to 750), which is due to the satellite group effect in combination with optimized hydrophilic/hydrophobic balance of the polymer backbone. © 2017
    view abstractdoi: 10.1016/j.polymer.2017.04.074
  • 2017 • 237 Nanoarmored Enzymes for Organic Enzymology: Synthesis and Characterization of Poly(2-Alkyloxazoline)–Enzyme Conjugates
    Leurs, M. and Tiller, J.C.
    Methods in Enzymology 590 413-444 (2017)
    The properties of enzymes can be altered significantly by modification with polymers. Numerous different methods are known to obtain such polymer–enzyme conjugates (PECs). However, there is no universal method to render enzymes into PECs that are fully soluble in organic solvents. Here, we present a method, which achieves such high degree of modification of proteins that the majority of modified enzymes will be soluble in organic solvents. This is achieved by preparing poly(2-alkyloxazoline)s (POx) with an NH2 end group and coupling this functional polymer via pyromellitic acid dianhydride onto the amino groups of the respective protein. The resulting PECs are capable of serving as surfactants for unmodified proteins, rendering the whole mixture organosoluble. Depending on the nature of the POx and the molecular weight and the nature of the enzyme, the PECs are soluble in chloroform or even toluene. Another advantage of this method is that the poly(2-alkyloxazoline) can be activated with the coupling agent and used for the enzyme conjugation without further purification. The POx–enzyme conjugates generated by this modification strategy show modulated catalytic activity in both, aqueous and organic, systems. © 2017 Elsevier Inc.
    view abstractdoi: 10.1016/bs.mie.2017.01.008
  • 2017 • 236 Improvement of virus removal using ultrafiltration membranes modified with grafted zwitterionic polymer hydrogels
    Lu, R. and Zhang, C. and Piatkovsky, M. and Ulbricht, M. and Herzberg, M. and Nguyen, T.H.
    Water Research 116 86-94 (2017)
    Potable water reuse has been adopted by cities suffering water scarcity in recent years. The microbial safety in water reuse, especially with respect to pathogenic viruses, is still a concern for water consumers. Membrane filtration can achieve sufficient removal of pathogenic viruses without disinfection byproducts, but the required energy is intensive. In this study, we graft-polymerized zwitterionic SPP ([3-(methacryloylamino) propyl] dimethyl (3-sulfopropyl) ammonium hydroxide) on a 150 kDa ultrafiltration polyethersulfone membrane to achieve a significantly higher virus removal. The redox-initiated graft-polymerization was performed in an aqueous solution during filtration of the monomer and initiators, allowing for functionalizing the membrane pores with hydrophilic polySPP. Bacteriophage MS2 and human adenovirus type 2 (HAdV-2) were used as surrogates for pathogenic human norovirus and human adenovirus. The grafting resulted in ∼18% loss of the membrane permeability but an increase of 4 log10 in HAdV-2 removal and 3 log10 in MS2 removal. The pristine and the grafted membranes were both conditioned with soluble microbial products (SMP) extracted from a full-scale membrane bioreactor (MBR) in order to test the virus removal after fouling the membranes. After fouling, the HAdV-2 removal by the grafted membrane was 1 log10 higher than that of the pristine membrane. For MS2, the grafted membrane after fouling with SMP achieved an additional 5 log10 removal compared to the unmodified membrane. The simple graft-polymerization functionalization of commercialized membrane achieving enhanced virus removal efficiency highlights the promise of membrane filtration for pathogen control in potable water reuse. © 2017
    view abstractdoi: 10.1016/j.watres.2017.03.023
  • 2017 • 235 Amorphous-amorphous phase separation in API/polymer formulations
    Luebbert, C. and Huxoll, F. and Sadowski, G. and Van Den Mooter, G. and Grohganz, H.
    Molecules 22 (2017)
    The long-term stability of pharmaceutical formulations of poorly-soluble drugs in polymers determines their bioavailability and therapeutic applicability. However, these formulations do not only often tend to crystallize during storage, but also tend to undergo unwanted amorphous-amorphous phase separations (APS). Whereas the crystallization behavior of APIs in polymers has been measured and modeled during the last years, the APS phenomenon is still poorly understood. In this study, the crystallization behavior, APS, and glass-transition temperatures formulations of ibuprofen and felodipine in polymeric PLGA excipients exhibiting different ratios of lactic acid and glycolic acid monomers in the PLGA chain were investigated by means of hot-stage microscopy and DSC. APS and recrystallization was observed in ibuprofen/PLGA formulations, while only recrystallization occurred in felodipine/PLGA formulations. Based on a successful modeling of the crystallization behavior using the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT), the occurrence of APS was predicted in agreement with experimental findings. © 2017 by the authors; licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/molecules22020296
  • 2017 • 234 Fabrication of nanoporous graphene/polymer composite membranes
    Madauß, L. and Schumacher, J. and Ghosh, M. and Ochedowski, O. and Meyer, J. and Lebius, H. and Ban-D'Etat, B. and Toimil-Molares, M.E. and Trautmann, C. and Lammertink, R.G.H. and Ulbricht, M. and Schleberger, M.
    Nanoscale 9 10487-10493 (2017)
    Graphene is currently investigated as a promising membrane material in which selective pores can be created depending on the requirements of the application. However, to handle large-area nanoporous graphene a stable support material is needed. Here, we report on composite membranes consisting of large-area single layer nanoporous graphene supported by a porous polymer. The fabrication is based on ion-track nanotechnology with swift heavy ions directly creating atomic pores in the graphene lattice and damaged tracks in the polymer support. Subsequent chemical etching converts the latent ion tracks in the supporting polymer foil, here polyethylene terephthalate (PET), into open microchannels while the perfectly aligned pores in the graphene top layer remain unaffected. To avoid unintentional damage creation and delamination of the graphene layer from the substrate, the graphene is encapsulated by a protecting poly(methyl methacrylate) (PMMA) layer. By this procedure a stable composite membrane is obtained consisting of nanoporous graphene (coverage close to 100%) suspended across selfaligned track-etched microchannels in a polymer support film. Our method presents a facile way to create high quality suspended graphene of tunable pore size supported on a flexible porous polymeric support, thus enabling the development of membranes for fast and selective ultrafiltration separation processes. This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c7nr02755a
  • 2017 • 233 Molecular dynamics simulations of entangled polymers: The effect of small molecules on the glass transition temperature
    Mahmoudinezhad, E. and Marquardt, A. and Eggeler, G. and Varnik, F.
    Procedia Computer Science 108 265-271 (2017)
    Effect of small molecules, as they penetrate into a polymer system, is investigated via molecular dynamics simulations. It is found that small spherical particles reduce the glass transition temperature and thus introduce a softening of the material. Results are compared to experimental findings for the effect of different types of small molecules such as water, acetone and ethanol on the glass transition temperature of a polyurethane-based shape memory polymer. Despite the simplicity of the simulated model, MD results are found to be in good qualitative agreement with experimental data. © 2017 The Authors. Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.procs.2017.05.152
  • 2017 • 232 Influence of PE-CVD and PE-ALD on defect formation in permeation barrier films on PET and correlation to atomic oxygen fluence
    Mitschker, F. and Steves, S. and Gebhard, M. and Rudolph, M. and Schücke, L. and Kirchheim, D. and Jaritz, M. and Brochhagen, M. and Hoppe, C. and Dahlmann, R. and Böke, M. and Benedikt, J. and Giner, I. and De los Arcos, T. and...
    Journal of Physics D: Applied Physics 50 (2017)
    doi: 10.1088/1361-6463/aa6e28
  • 2017 • 231 Poly(2-ethyloxazoline) as matrix for highly active electrospun enzymes in organic solvents
    Plothe, R. and Sittko, I. and Lanfer, F. and Fortmann, M. and Roth, M. and Kolbach, V. and Tiller, J.C.
    Biotechnology and Bioengineering 114 39-45 (2017)
    Nanofibers are advantageous carriers for biocatalysts, because they show lower diffusion limitations due to their high surface/volume ratio. Only a few samples are known where enzymes are directly spun into nanofibers, mostly because there are not many suited polymer carriers. In this study, poly(2-ethyloxazoline) (PEtOx) was explored regarding its usefulness to activate various enzymes in organic solvents by directly electrospinning them from aqueous solutions containing the polymer. It was found that the concentration of PEtOx in the spinning solution and also the swellability of the fibers play a great role in the activity of the enzymes in organic solvents. Using electrospun lipase B from Candida antarctica (CaLB) under optimized conditions revealed a higher carrier activity than the commercial Novozyme 435 with 10 times less immobilized protein. The electrospinning of PEtOx/CaLB fibers onto a stirrer is used to realize a biocatalytic stirrer for organic solvents. Biotechnol. Bioeng. 2017;114: 39–45. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.
    view abstractdoi: 10.1002/bit.26043
  • 2017 • 230 Multiaxial Reinforcement of Cross-Linked Isotactic Poly(propylene) upon Uniaxial Stretching
    Raidt, T. and Hoeher, R. and Katzenberg, F. and Tiller, J.C.
    Macromolecular Materials and Engineering 302 (2017)
    Isotactic poly(propylene) (iPP) is one of a few polymers that show homoepitaxy, i.e., the formed crystals act as nuclei for so-called daughter crystals that are formed nearly perpendicular to the backbones of the primary crystallized mother crystals. Lightly cross-linked isotactic poly(propylene) (x-iPP) offers the opportunity to form nearly all mother crystals in stretching direction and simultaneously allow formation of daughter crystals. Since crystals in polymers act as reinforcement along chain direction, this unique behavior allows multiaxial reinforcement in iPP induced only by stretching in one direction. In this study the influence of applied uniaxial strain is explored on the resulting multiaxial crystal orientations and Young's moduli parallel, perpendicular as well as under an angle of 45° to the stretching direction of the sample. It is shown that the occurring multiaxial orientations strongly depend on applied strain during crystallization and cause significantly improved Young's moduli parallel as well as perpendicular to the prior stretching direction while that under an angle of 45° is slightly decreasing. The here described technique to obtain multiaxially oriented morphologies is not restricted to thin films but can be efficiently applied also to bulk samples. (Figure presented.). © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/mame.201600308
  • 2017 • 229 A Self-Powered Ethanol Biosensor
    Ruff, A. and Pinyou, P. and Nolten, M. and Conzuelo, F. and Schuhmann, W.
    ChemElectroChem 4 890-897 (2017)
    We describe the fabrication of a self-powered ethanol biosensor comprising a β-NAD+-dependent alcohol dehydrogenase (ADH) bioanode and a bienzymatic alcohol oxidase (AOx) and horseradish peroxidase (HRP) biocathode. β-NAD+ is regenerated by means of a specifically designed phenothiazine dye (i.e. toluidine blue, TB) modified redox polymer in which TB was covalently anchored to a hexanoic acid tethered poly(4-vinylpyridine) backbone. The redox polymer acts as an immobilization matrix for ADH. Using a carefully chosen anchoring strategy through the formation of amide bonds, the potential of the TB-based mediator is shifted to more positive potentials, thus preventing undesired O2 reduction. To counterbalance the rather high potential of the TB-modified polymer, and thus the bioanode, a high-potential AOx/HRP-based biocathode is suggested. HRP is immobilized in a direct-electron-transfer regime on screen-printed graphite electrodes functionalized with multi-walled carbon nanotubes. The nanostructured cathode ensures the wiring of the iron-oxo complex within oxidized HRP, and thus a high potential for the reduction of H2O2 of about +550mV versus Ag/AgCl/3M KCl. The proposed biofuel cell exhibits an open-circuit voltage (OCV) of approximately 660mV and was used as self-powered device for the determination of the ethanol content in liquor. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/celc.201600864
  • 2017 • 228 Bipyridine copper functionalized polymer resins as support materials for the aerobic oxidation of alcohols
    Sand, H. and Weberskirch, R.
    Polymer International 66 428-435 (2017)
    Here, we report the first polymer resin supported Cu(I)/bipyridine/N-oxyl catalyst systems for the aerobic oxidation of alcohols at room temperature with ambient air. We chose polystyrene-poly(ethylene glycol) copolymer (TentaGel®) and Merrifield resin as support materials because of their different swelling properties in polar and nonpolar solvents. The bromo functionalized TentaGel resin TG1 or Merrifield resin MR1 were functionalized with 4,4′-dimethoxy-2,2′-bipyridine (MeObpy) to give the ligand modified polymer resin TG2/MR2 that was loaded with CuI(Br) to give the final CuI(Br)/bipyridine support TG3/MR3. These resins were characterized by Fourier transform infrared, SEM, SEM energy dispersive X-ray spectroscopy and elemental analysis. Catalytic activity and recyclability of TG3 was investigated in acetonitrile and cyclohexane and displayed high activities in acetonitrile but also high metal leaching. In cyclohexane as solvent leaching was reduced to 1% − 2%, and catalytic activity was still at 75% after the fifth run. MR3 was consequently tested in cyclohexane and toluene. In both solvents low metal leaching was observed with higher activity in toluene as solvent, showing still over 90% conversion after the seventh run with 9-azabicyclo[3.3.1]nonane N-oxyl (ABNO) and 80% with 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO). © 2016 Society of Chemical Industry. © 2016 Society of Chemical Industry
    view abstractdoi: 10.1002/pi.5277
  • 2017 • 227 Investigations on "near perfect" poly(2-oxazoline) based amphiphilic polymer conetworks with a crystallizable block
    Schmidt, M. and Raidt, T. and Ring, S. and Gielke, S. and Gramse, C. and Wilhelm, S. and Katzenberg, F. and Krumm, C. and Tiller, J.C.
    European Polymer Journal 88 562-574 (2017)
    Amphiphilic polymer conetworks (APCNs) of near perfect structure were prepared by cross-linking defined poly(2-oxazoline)-based block copolymers. To this end, ABA triblock copolymers with poly(2-methyloxazoline) (PMOx) as A block and poly(2-heptyloxazoline) (PHepOx) as B block in different compositions and with different cross-linkable end groups were prepared and crosslinked. The resulting amphiphilic polymer conetworks were characterized with atomic force microscopy (AFM) and small as well as wide angle X-ray scattering (SAXS/WAXS). The results show that the PHepOx block crystallizes in the APCNs if the content is larger than 19. vol.%, but shows no thermal signature in the differential scanning calorimetry if the polymer content is below 68. vol.%. Further, the size of the polymer phase is the same in a composition range of 38-58. vol.% PHepOx. The phase size was confirmed by AFM. The found very regular interconnected structure over a wide range of compositions seems to be the generic structural motive in APCNs and is also formed when inserting a crystallizable polymer block. © 2016 Elsevier Ltd.
    view abstractdoi: 10.1016/j.eurpolymj.2016.09.046
  • 2017 • 226 The collective behavior of spring-like motifs tethered to a DNA origami nanostructure
    Schöneweiß, E.-C. and Saccà, B.
    Nanoscale 9 4486-4496 (2017)
    Dynamic DNA nanotechnology relies on the integration of small switchable motifs at suitable positions of DNA nanostructures, thus enabling the manipulation of matter with nanometer spatial accuracy in a trigger-dependent fashion. Typical examples of such motifs are hairpins, whose elongation into duplexes can be used to perform long-range, translational movements. In this work, we used temperature-dependent FRET spectroscopy to determine the thermal stabilities of distinct sets of hairpins integrated into the central seam of a DNA origami structure. We then developed a hybrid spring model to describe the energy landscape of the tethered hairpins, combining the thermodynamic nearest-neighbor energy of duplex DNA with the entropic free energy of single-stranded DNA estimated using a worm-like chain approximation. We show that the organized scaffolding of multiple hairpins enhances the thermal stability of the device and that the coordinated action of the tethered motors can be used to mechanically unfold a G-quadruplex motif bound to the inner cavity of the origami structure, thus surpassing the operational capabilities of freely diffusing motors. Finally, we increased the complexity of device functionality through the insertion of two sets of parallel hairpins, resulting in four distinct states and in the reversible localization of desired molecules within the reconfigurable regions of the origami architecture. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6nr08314e
  • 2017 • 225 Consecutive imprinting performance of large area UV nanoimprint lithography using Bi-layer soft stamps in ambient atmosphere
    Si, S. and Hoffmann, M.
    Microelectronic Engineering 176 62-70 (2017)
    For UV nanoimprint lithography (UV-NIL) using polymer soft stamps, imprinting at ambient atmosphere brings additional challenges due to evaporated solvents and possible byproducts resulting from the interaction between the UV light, oxygen and the polymer-based material. Moreover, the Laplace pressure may impact differently on the capillary filling for both positive and negative patterns at atmospheric pressure compared to that in the vacuum. Twenty consecutive imprints using bi-layer Polydimethylsiloxane (PDMS), PDMS/toluene-diluted PDMS, PDMS/X-PDMS, PDMS/vvsPDMS stamps have been tracked and inspected. The imprinting employs a center-to-edge scheme in ambient atmosphere. The results show that high reusability and imprint uniformity can be achieved for at least twenty consecutive imprints using the pure PDMS (PDMS/PDMS) and PDMS/toluene-diluted PDMS. These stamps can overcome the challenges of the interaction between the UV light, oxygen and the polymer-based materials. The Laplace pressure under atmosphere does not hinder the resist filling for such consecutive imprints. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.mee.2017.01.032
  • 2017 • 224 Interrogation of a PS1-Based Photocathode by Means of Scanning Photoelectrochemical Microscopy
    Zhao, F. and Plumeré, N. and Nowaczyk, M.M. and Ruff, A. and Schuhmann, W. and Conzuelo, F.
    Small 13 (2017)
    In the development of photosystem-based energy conversion devices, the in-depth understanding of electron transfer processes involved in photocurrent generation and possible charge recombination is essential as a basis for the development of photo-bioelectrochemical architectures with increased efficiency. The evaluation of a bio-photocathode based on photosystem 1 (PS1) integrated within a redox hydrogel by means of scanning photoelectrochemical microscopy (SPECM) is reported. The redox polymer acts as a conducting matrix for the transfer of electrons from the electrode surface to the photo-oxidized P700 centers within PS1, while methyl viologen is used as charge carrier for the collection of electrons at the reduced FB site of PS1. The analysis of the modified surfaces by SPECM enables the evaluation of electron-transfer processes by simultaneously monitoring photocurrent generation at the bio-photoelectrode and the associated generation of reduced charge carriers. The possibility to visualize charge recombination processes is illustrated by using two different electrode materials, namely Au and p-doped Si, exhibiting substantially different electron transfer kinetics for the reoxidation of the methyl viologen radical cation used as freely diffusing charge carrier. In the case of p-doped Si, a slower recombination kinetics allows visualization of methyl viologen radical cation concentration profiles from SPECM approach curves. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/smll.201604093
  • 2016 • 223 Theoretical framework of modeling of ionic EAPs within the Theory of Porous Media
    Bluhm, J. and Serdas, S. and Schröder, J.
    Archive of Applied Mechanics 86 3-19 (2016)
    A thermo-electromechanical formulation for the description of ionic electroactive polymers is derived within the framework of the Theory of Porous Media. The model consists of an electrically charged porous solid saturated with an ionic solution. The saturated porous medium is assumed to be incompressible. Different constituents following different kinematic paths are considered such as solid, fluid, anions, cations and free charges. The electromechanical and the electrodynamic field equations are discussed. Based on the second law of thermodynamics, a consistent model is developed. With respect to the closure problem of the model, the needed constitutive relations and evolution equations are presented. © 2016, Springer-Verlag Berlin Heidelberg.
    view abstractdoi: 10.1007/s00419-015-1110-8
  • 2016 • 222 Towards a physics-based multiscale modelling of the electro-mechanical coupling in electro-active polymers
    Cohen, N. and Menzel, A. and DeBotton, G.
    Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 472 (2016)
    Owing to the increasing number of industrial applications of electro-active polymers (EAPs), there is a growing need for electromechanical models which accurately capture their behaviour. To this end, we compare the predicted behaviour of EAPs undergoing homogeneous deformations according to three electromechanical models. The first model is a phenomenological continuumbased model composed of the mechanical Gent model and a linear relationship between the electric field and the polarization. The electrical and the mechanical responses according to the second model are based on the physical structure of the polymer chain network. The third model incorporates a neo-Hookean mechanical response and a physically motivated microstructurally based long-chains model for the electrical behaviour. In the microstructural-motivated models, the integration from the microscopic to the macroscopic levels is accomplished by the micro-sphere technique. Four types of homogeneous boundary conditions are considered and the behaviours determined according to the three models are compared. For the microstructurally motivated models, these analyses are performed and compared with the widely used phenomenological model for the first time. Some of the aspects revealed in this investigation, such as the dependence of the intensity of the polarization field on the deformation, highlight the need for an in-depth investigation of the relationships between the structure and the behaviours of the EAPs at the microscopic level and their overall macroscopic response. © 2016 The Author(s) Published by the Royal Society. All rights reserved.
    view abstractdoi: 10.1098/rspa.2015.0462
  • 2016 • 221 Improved Antifouling Properties of Polydimethylsiloxane Films via Formation of Polysiloxane/Polyzwitterion Interpenetrating Networks
    Dundua, A. and Franzka, S. and Ulbricht, M.
    Macromolecular Rapid Communications 37 2030-2036 (2016)
    Nonspecific adsorption of proteins is a challenging problem for the development of biocompatible materials, as well as for antifouling and fouling-release coatings, for instance for the marine industry. The concept of preparing amphiphilic systems based on low surface energy hydrophobic materials via their hydrophilic modification is being widely pursued. This work describes a novel two-step route for the preparation of interpenetrating polymer networks of otherwise incompatible poly(dimethylsiloxane) and zwitterionic polymers. Changes in surface hydrophilicity as well as surface charge at different pH values are investigated. Characterization using atomic force microscopy provides thorough insight into surface changes upon hydrophilic modification. Protein fouling of the materials is assessed using fibrinogen as a model protein. (Figure presented.). © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/marc.201600473
  • 2016 • 220 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 abstractdoi: 10.1016/j.jcis.2016.06.034
  • 2016 • 219 Finite element simulation of rate-dependent magneto-active polymer response
    Haldar, K. and Kiefer, B. and Menzel, A.
    Smart Materials and Structures 25 (2016)
    This contribution is concerned with the embedding of constitutive relations for magneto-active polymers (MAP) into finite element simulations. To this end, a recently suggested, calibrated, and validated material model for magneto-mechanically coupled and rate-dependent MAP response is briefly summarized in its continuous and algorithmic settings. Moreover, the strongly coupled field equations of finite deformation magneto-mechanics are reviewed. For the purpose of numerical simulation, a finite element model is then established based on the usual steps of weak form representation, discretization and consistent linearization. Two verifying inhomogeneous numerical examples are presented in which a classical 'plate with a hole' geometry is equipped with MAP properties and subjected to different types of time-varying mechanical and magnetic loading. © 2016 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0964-1726/25/10/104003
  • 2016 • 218 Non-monotonic course of protein solubility in aqueous polymer-salt solutions can be modeled using the sol-mxDLVO model
    Herhut, M. and Brandenbusch, C. and Sadowski, G.
    Biotechnology Journal 11 282-289 (2016)
    Protein purification is often performed using cost-intensive chromatographic steps. To discover economic alternatives (e.g., crystallization), knowledge on protein solubility as a function of temperature, pH, and additives in solution as well as their concentration is required. State-of-the-art models for predicting protein solubility almost exclusively consider aqueous salt systems, whereas "salting-in" and "salting-out" effects induced by the presence of an additional polymer are not considered. Thus, we developed the sol-mxDLVO model. Using this newly developed model, protein solubility in the presence of one salt and one polymer, especially the non-monotonic course of protein solubility, could be predicted. Systems considered included salts (NaCl, Na-p-Ts, (NH4)2SO4) and the polymer polyethylene glycol (MW: 2000 g/mol, 12000 g/mol) and proteins lysozyme from chicken egg white (pH 4 to 5.5) and D-xylose ketol-isomerase (pH 7) at 298.15 K. The results show that by using the sol-mxDLVO model, protein solubility in polymer-salt solutions can be modeled in good agreement with the experimental data for both proteins considered. The sol-mxDLVO model can describe the non-monotonic course of protein solubility as a function of polymer concentration and salt concentration, previously not covered by state-of-the-art models. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/biot.201500123
  • 2016 • 217 Inclusion of mPRISM potential for polymer-induced protein interactions enables modeling of second osmotic virial coefficients in aqueous polymer-salt solutions
    Herhut, M. and Brandenbusch, C. and Sadowski, G.
    Biotechnology Journal 11 146-154 (2016)
    The downstream processing of therapeutic proteins is a challenging task. Key information needed to estimate applicable workup strategies (e.g. crystallization) are the interactions of the proteins with other components in solution. This information can be deduced from the second osmotic virial coefficient B22, measurable by static light scattering. Thermodynamic models are very valuable for predicting B22 data for different process conditions and thus decrease the experimental effort. Available B22 models consider aqueous salt solutions but fail for the prediction of B22 if an additional polymer is present in solution. This is due to the fact that depending on the polymer concentration protein-protein interactions are not rectified as assumed within these models. In this work, we developed an extension of the xDLVO model to predict B22 data of proteins in aqueous polymer-salt solutions. To show the broad applicability of the model, lysozyme, γ-globulin and D-xylose ketol isomerase in aqueous salt solution containing polyethylene glycol were considered. For all proteins considered, the modified xDLVO model was able to predict the experimentally observed non-monotonical course in B22 data with high accuracy. When used in an early stage in process development, the model will contribute to an efficient and cost effective downstream processing development. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/biot.201500086
  • 2016 • 216 Degradation of Polymeric Brominated Flame Retardants: Development of an Analytical Approach Using PolyFR and UV Irradiation
    Koch, C. and Dundua, A. and Aragon-Gomez, J. and Nachev, M. and Stephan, S. and Willach, S. and Ulbricht, M. and Schmitz, O. J. and Schmidt, T. C. and Sures, B.
    Environmental Science & Technology 50 12912--12920 (2016)
    Many well-established methods for studying the degradation of brominated flame retardants are not useful when working with polymeric and water insoluble species. An example for this specific class of flame retardants is PoIyFR (polymeric flame retardant; CAS No 1195978-93-8), which is used as a substituent for hexabromocyclododecane. Although it has been on the market for two years now, almost no information is available about its long time behavior in the environment. Within this study, we focus on how to determine a possible degradation of both pure PolyFR as well as PolyFR in the final insulation product, expanded polystyrene foam. Therefore, we chose UV radiation followed by analyses of the total bromine content at different time points via ICP-MS and identified possible degradation products such as 2,4,6-tribromophenol through LC-MS. These results were then linked with measurements of the adsorbable organically bound bromine and total organic carbon in order to estimate their concentrations. With respect to the obtained H-1 NMR, GPC, and contact angle results, the possibility for further degradation was discussed, as UV irradiation can influence the decomposition of molecules in combination with other environmental factors like biodegradation.
    view abstractdoi: 10.1021/acs.est.6b04083
  • 2016 • 215 Composites of fluoroapatite and methylmethacrylate-based polymers (PMMA) for biomimetic tooth replacement
    Lübke, A. and Enax, J. and Wey, K. and Fabritius, H.-O. and Raabe, D. and Epple, M.
    Bioinspiration and Biomimetics 11 (2016)
    Synthetic composite materials that mimic the structure and composition of mammalian tooth enamel were prepared by mixing fluoroapatite rods (diameter 2-3 μm, thickness about 0.5 μm) and methylmethacrylate (MMA), followed by polymerization either during or immediately after ultracentrifugation, using either a tertiary amine/radical initiator for polymerization at room temperature or a radical initiator for thermal polymerization. This led to mineral-rich composites (mineral content between 50 and 75 wt%). To enhance the mechanical stability and the interaction between fluoroapatite and polymer matrix, small amounts of differently functionalized MMA monomers were added to the co-monomer mixture. Another approach was the coating of the fluoroapatite rods with silica and the polymerization in the presence of a siloxane-functionalized MMA monomer. The hardness of the composites was about 0.2-0.4 GPa as determined by Vickers indentation tests, about 2 times higher than the polymer matrix alone. The composites had a good resistance against acids (60 min at pH 3, 37 °C). © 2016 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1748-3190/11/3/035001
  • 2016 • 214 Diffusion of small molecules in a shape memory polymer
    Marquardt, A. and Mogharebi, S. and Neuking, K. and Varnik, F. and Eggeler, G.
    Journal of Materials Science 51 9792-9804 (2016)
    The present work studies the diffusion of small molecules (acetone, ethanol, and water) in a shape memory polymer (SMP) of type Estane ETE 75DT3 (SMP-E), which represents a thermoplastic polyurethane. The work aims at providing background information on the chemical reaction between SMPs and small molecules which can limit the service life of SMP actuators operating in harsh chemical environments. Weight gain studies after immersion of plate specimens in liquid acetone, ethanol, and water yield data which can be assessed on the basis of analytical and numerical solutions of Fick’s second law. The diffusion coefficients which are obtained for 21, 30, and 40 °C in the present study scale as Dacetone > Dethanol > Dwater. The diffusion coefficients show Arrhenius types of temperature dependencies with apparent activation energies of 33 (acetone), 59 (ethanol), and 58 (water) kJ mol−1. The diffusion coefficients and the apparent activation energies obtained in the present work are in reasonable agreement with data which were reported for the reaction of the three small molecules with similar polymers in the literature. It is not straightforward to correlate differences in molecular mobility with individual physical properties. The Hansen solubility parameter (originally derived to explain solubility not mobility) qualitatively rationalizes the observed differences. © 2016, Springer Science+Business Media New York.
    view abstractdoi: 10.1007/s10853-016-0213-0
  • 2016 • 213 Assessing biofouling resistance of a polyamide reverse osmosis membrane surface-modified with a zwitterionic polymer
    Marré Tirado, M.L. and Bass, M. and Piatkovsky, M. and Ulbricht, M. and Herzberg, M. and Freger, V.
    Journal of Membrane Science 520 490-498 (2016)
    Desalination and water treatment by reverse osmosis (RO) can highly increase clean water supply in today's world. However, biofouling of polyamide (PA) RO membranes is a serious obstacle for a wider use of this technology. One of the promising ways of biofouling control is membranes surface modification with zwitterionic polymers. A number of published works showed that zwitterionic coatings can improve the resistance of PA membranes to the initial bacteria adhesion, however no long-term experiments with real treated water effluents were conducted. In this work a commercial PA RO membrane was surface-modified with a zwitterionic polymer and its resistance to biofouling was tested in both short-term bacteria adhesion experiments and longer filtration tests conducted using real treated wastewater effluents, spiked with a small level of nutrients. The obtained results showed that, initially, there was a clear improvement in the biofouling resistance of the modified membranes and their permeation flux remained stable, in contrast to the non-modified counterpart. However, eventually, the permeabilities of the two membranes declined to a similar degree. The results indicate that antifouling coatings might not promise a better membrane performance in long term. The analysis of the biofilms grown on the pristine and the modified membranes suggested that adaptation capabilities of biofilms overcame the favorable changes in surface properties of the membrane achieved by the modification. The presented results emphasized the importance of long-term filtration experiments as an ultimate test for assessing biofouling resistance of the modified desalination membranes. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2016.07.027
  • 2016 • 212 A Nernstian Biosupercapacitor
    Pankratov, D. and Conzuelo, F. and Pinyou, P. and Alsaoub, S. and Schuhmann, W. and Shleev, S.
    Angewandte Chemie - International Edition 55 15434-15438 (2016)
    We propose the very first “Nernstian biosupercapacitor”, a biodevice based on only one redox polymer: poly(vinyl imidazole-co-allylamine)[Os(bpy)2Cl], and two biocatalysts. At the bioanode PQQ-dependent glucose dehydrogenase reduces the Os3+ moieties at the polymer to Os2+ shifting the Nernst potential of the Os3+/Os2+ redox couple to negative values. Concomitantly, at the biocathode the reduction of O2 by means of bilirubin oxidase embedded in the same redox polymer leads to the oxidation of Os2+ to Os3+ shifting the Nernst potential to higher values. Despite the use of just one redox polymer an open circuit voltage of more than 0.45 V was obtained during charging and the charge is stored in the redox polymer at both the bioanode and the biocathode. By connecting both electrodes via a predefined resistor a high power density is obtained for a short time exceeding the steady state power of a corresponding biofuel cell by a factor of 8. © 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/anie.201607144
  • 2016 • 211 Wiring of the aldehyde oxidoreductase PaoABC to electrode surfaces via entrapment in low potential phenothiazine-modified redox polymers
    Pinyou, P. and Ruff, A. and Pöller, S. and Alsaoub, S. and Leimkühler, S. and Wollenberger, U. and Schuhmann, W.
    Bioelectrochemistry 109 24-30 (2016)
    Phenothiazine-modified redox hydrogels were synthesized and used for the wiring of the aldehyde oxidoreductase PaoABC to electrode surfaces. The effects of the pH value and electrode surface modification on the biocatalytic activity of the layers were studied in the presence of vanillin as the substrate. The enzyme electrodes were successfully employed as bioanodes in vanillin/O2 biofuel cells in combination with a high potential bilirubin oxidase biocathode. Open circuit voltages of around 700mV could be obtained in a two compartment biofuel cell setup. Moreover, the use of a rather hydrophobic polymer with a high degree of crosslinking sites ensures the formation of stable polymer/enzyme films which were successfully used as bioanode in membrane-less biofuel cells. © 2015 Elsevier B.V.
    view abstractdoi: 10.1016/j.bioelechem.2015.12.005
  • 2016 • 210 Design of an Os Complex-Modified Hydrogel with Optimized Redox Potential for Biosensors and Biofuel Cells
    Pinyou, P. and Ruff, A. and Pöller, S. and Ma, S. and Ludwig, R. and Schuhmann, W.
    Chemistry - A European Journal 22 5319-5326 (2016)
    Multistep synthesis and electrochemical characterization of an Os complex-modified redox hydrogel exhibiting a redox potential ≈+30 mV (vs. Ag/AgCl 3 m KCl) is demonstrated. The careful selection of bipyridine-based ligands bearing N,N-dimethylamino moieties and an amino-linker for the covalent attachment to the polymer backbone ensures the formation of a stable redox polymer with an envisaged redox potential close to 0 V. Most importantly, the formation of an octahedral N6-coordination sphere around the Os central atoms provides improved stability concomitantly with the low formal potential, a low reorganization energy during the Os3+/2+ redox conversion and a negligible impact on oxygen reduction. By wiring a variety of enzymes such as pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase, flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase and the FAD-dependent dehydrogenase domain of cellobiose dehydrogenase, low-potential glucose biosensors could be obtained with negligible co-oxidation of common interfering compounds such as uric acid or ascorbic acid. In combination with a bilirubin oxidase-based biocathode, enzymatic biofuel cells with open-circuit voltages of up to 0.54 V were obtained. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/chem.201504591
  • 2016 • 209 Nanocasting Design and Spatially Selective Sulfonation of Polystyrene-Based Polymer Networks as Solid Acid Catalysts
    Richter, F.H. and Sahraoui, L. and Schüth, F.
    Chemistry - A European Journal 22 13563-13574 (2016)
    Nanocasting is a general and widely applied method in the generation of porous materials during which a sacrificial solid template is used as a mold on the nanoscale. Ideally, the resulting structure is the inverse of the template. However, replication is not always as direct as anticipated, so the influences of the degree of pore filling and of potential restructuring processes after removal of the template need to be considered. These apparent limitations give rise to opportunities in the synthesis of poly(styrene-co-divinylbenzene) (PSD) polymer networks of widely varying porosities (BET surface area=63–562 m2g−1; Vtot=0.18–1.05 cm3g−1) by applying a single synthesis methodology. In addition, spatially selective sulfonation on the nanoscale seems possible. Together, nanocasting and sulfonation enable rational catalyst design. The highly porous nanocast and predominantly surface-sulfonated PSD networks approach the activity of the corresponding molecular catalyst, para-toluenesulfonic acid, and exceed those of commercial ion-exchange polymers in the depolymerization of macromolecular inulin. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/chem.201603069
  • 2016 • 208 Investigation of the pH-Dependent Impact of Sulfonated Polyaniline on Bioelectrocatalytic Activity of Xanthine Dehydrogenase
    Sarauli, D. and Borowski, A. and Peters, K. and Schulz, B. and Fattakhova-Rohlfing, D. and Leimkühler, S. and Lisdat, F.
    ACS Catalysis 6 7152-7159 (2016)
    We report on the pH-dependent bioelectrocatalytic activity of the redox enzyme xanthine dehydrogenase (XDH) in the presence of sulfonated polyaniline PMSA1 (poly(2-methoxyaniline-5-sulfonic acid)-co-aniline). Ultraviolet-visible (UV-vis) spectroscopic measurements with both components in solution reveal electron transfer from the hypoxanthine (HX)-reduced enzyme to the polymer. The enzyme shows bioelectrocatalytic activity on indium tin oxide (ITO) electrodes, when the polymer is present. Depending on solution pH, different processes can be identified. It can be demonstrated that not only product-based communication with the electrode but also efficient polymer-supported bioelectrocatalysis occur. Interestingly, substrate-dependent catalytic currents can be obtained in acidic and neutral solutions, although the highest activity of XDH with natural reaction partners is in the alkaline region. Furthermore, operation of the enzyme electrode without addition of the natural cofactor of XDH is feasible. Finally, macroporous ITO electrodes have been used as an immobilization platform for the fabrication of HX-sensitive electrodes. The study shows that the efficient polymer/enzyme interaction can be advantageously combined with the open structure of an electrode material of controlled pore size, resulting in good processability, stability, and defined signal transfer in the presence of a substrate. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acscatal.6b02011
  • 2016 • 207 Tuning the Cell Adhesion on Biofunctionalized Nanoporous Organic Frameworks
    Schmitt, S. and Hümmer, J. and Kraus, S. and Welle, A. and Grosjean, S. and Hanke-Roos, M. and Rosenhahn, A. and Bräse, S. and Wöll, C. and Lee-Thedieck, C. and Tsotsalas, M.
    Advanced Functional Materials 26 8455-8462 (2016)
    The ability to control the structure and surface chemistry of biomaterials on a molecular level is crucial for optimizing their performance. Here, a novel type of nanoporous organic framework that is suited for the fabrication of thin films is described. These surface-grafted gels (SURGELs) are prepared and functionalized using two orthogonal, metal-free click chemistries. The SURGELs are shown to be cytocompatible and to efficiently mediate adhesion of osteoblast-like cells. This process can be further enhanced by surface modification. In addition, the use of light-triggered reactions in combination with photomasks allows a patterned functionalization of the substrates. The potential to vary and exactly adjust the parameters within the SURGEL polymer network (including porosity and exact network topology on the nanometer scale as well as addressable functional groups) combined with the ability to functionalize their surfaces with any clickable biomolecule of choice in any desired pattern allow the targeted design of novel SURGEL-based biomaterials for applications in nanomedicine, tissue engineering scaffolds, wound dressing,and medical implants. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/adfm.201603054
  • 2016 • 206 Oxygen and ammonia plasma treatment of poly(3-hydroxybutyrate) films for controlled surface zeta potential and improved cell compatibility
    Syromotina, D.S. and Surmenev, R.A. and Surmeneva, M.A. and Boyandin, A.N. and Epple, M. and Ulbricht, M. and Oehr, C. and Volova, T.G.
    Materials Letters 163 277-280 (2016)
    The oxygen and ammonia radio-frequency (RF) plasma treatment of poly(3-hydroxybutyrate) P3HB films was performed. We revealed significant changes in the topography, a decrease in the surface zeta potential from -63 to -75 mV after the oxygen-plasma treatment and an increase after ammonia plasma treatment from -63 to -45 mV at a pH of 7.4. Investigations into the NIH 3T3 fibroblast adhesion and growth demonstrated the best cell vitality and a higher cell number for the ammonia plasma treatment at 150 W. © 2015 Elsevier B.V.
    view abstractdoi: 10.1016/j.matlet.2015.10.080
  • 2016 • 205 Spearhead Nanometric Field-Effect Transistor Sensors for Single-Cell Analysis
    Zhang, Y. and Clausmeyer, J. and Babakinejad, B. and López Córdoba, A. and Ali, T. and Shevchuk, A. and Takahashi, Y. and Novak, P. and Edwards, C. and Lab, M. and Gopal, S. and Chiappini, C. and Anand, U. and Magnani, L. and Co...
    ACS Nano 10 3214-3221 (2016)
    Nanometric field-effect-transistor (FET) sensors are made on the tip of spear-shaped dual carbon nanoelectrodes derived from carbon deposition inside double-barrel nanopipettes. The easy fabrication route allows deposition of semiconductors or conducting polymers to comprise the transistor channel. A channel from electrodeposited poly pyrrole (PPy) exhibits high sensitivity toward pH changes. This property is exploited by immobilizing hexokinase on PPy nano-FETs to give rise to a selective ATP biosensor. Extracellular pH and ATP gradients are key biochemical constituents in the microenvironment of living cells; we monitor their real-time changes in relation to cancer cells and cardiomyocytes. The highly localized detection is possible because of the high aspect ratio and the spear-like design of the nano-FET probes. The accurately positioned nano-FET sensors can detect concentration gradients in three-dimensional space, identify biochemical properties of a single living cell, and after cell membrane penetration perform intracellular measurements. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acsnano.5b05211
  • 2015 • 204 Design of Thermally Responsive Polymeric Hydrogels for Brackish Water Desalination: Effect of Architecture on Swelling, Deswelling, and Salt Rejection
    Ali, W. and Gebert, B. and Hennecke, T. and Graf, K. and Ulbricht, M. and Gutmann, J.S.
    ACS Applied Materials and Interfaces 7 15696-15706 (2015)
    In this work, we explore the ability of utilizing hydrogels synthesized from a temperature-sensitive polymer and a polyelectrolyte to desalinate salt water by means of reversible thermally induced absorption and desorption. Thus, the influence of the macromolecular architecture on the swelling/deswelling behavior for such hydrogels was investigated by tailor-made network structures. To this end, a series of chemically cross-linked polymeric hydrogels were synthesized via free radical-initiated copolymerization of sodium acrylate (SA) with the thermoresponsive comonomer N-isopropylacrylamide (NIPAAm) by realizing different structural types. In particular, two different polyNIPAAm macromonomers, either with one acrylate function at the chain end or with additional acrylate functions as side groups were synthesized by controlled polymerization and subsequent polymer-analogous reaction and then used as building blocks. The rheological behaviors of hydrogels and their estimated mesh sizes are discussed. The performance of the hydrogels in terms of swelling and deswelling in both deionized water (DI) and brackish water (2 g/L NaCl) was measured as a function of cross-linking degree and particle size. The salt content could be reduced by 23% in one cycle by using the best performing material. (Figure Presented). © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acsami.5b03878
  • 2015 • 203 Distortion of Ultrathin Photocleavable Block Copolymer Films during Photocleavage and Nanopore Formation
    Altinpinar, S. and Zhao, H. and Ali, W. and Kappes, R.S. and Schuchardt, P. and Salehi, S. and Santoro, G. and Theato, P. and Roth, S.V. and Gutmann, J.S.
    Langmuir 31 8947-8952 (2015)
    Highly ordered block copolymer thin films have been studied extensively during the last years because they afford versatile self-assembled morphologies via a bottom-up approach. They promise to be used in applications such as polymeric membranes or templates for nanostructured materials. Among the block copolymer structures, perpendicular cylinders have received strong attention due to their ability to fabricate highly ordered nanopores and nanowires. Nanopores can be created from a thin block copolymer film upon the removal of one block by selective etching or by dissolution of one polymer block. Here we demonstrate the utilization of polystyrene-block-poly(ethylene oxide) diblock copolymer (PS-hν-PEO) with an ortho-nitrobenzyl ester (ONB) as the photocleavable block-linker to create highly ordered thin films. Removal of the PEO block by choosing an appropriate solvent upon photocleavage is expected to yield arrays of nanopores decorated with functional groups, thus lending itself to adsorption or filtration uses. While the feasibility of this approach has been demonstrated, it is crucial to understand the influence of removal conditions (i.e., efficiency of photocleavage as well as best washing solvent) and to evaluate changes in the surface topology and inner structure upon photocleavage. To this end, the time dependence evolution of the surface morphology of block copolymer thin films was studied using grazing-incidence small-angle X-ray scattering (GISAXS) technique in combination with scanning probe microscopy. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.5b00750
  • 2015 • 202 Role of Polymer Fractionation in Energetic Losses and Charge Carrier Lifetimes of Polymer: Fullerene Solar Cells
    Baran, D. and Vezie, M.S. and Gasparini, N. and Deledalle, F. and Yao, J. and Schroeder, B.C. and Bronstein, H. and Ameri, T. and Kirchartz, T. and McCulloch, I. and Nelson, J. and Brabec, C.J.
    Journal of Physical Chemistry C 119 19668-19673 (2015)
    Nonradiative recombination reduces the open-circuit voltage relative to its theoretical limit and leads to reduced luminescence emission at a given excitation. Therefore, it is possible to correlate changes in luminescence emission with changes in open-circuit voltage and in the charge carrier lifetime. Here we use luminescence studies combined with transient photovoltage and differential charging analyses to study the effect of polymer fractionation in indacenoedithiophene-co-benzothiadiazole (IDTBT):fullerene solar cells. In this system, polymer fractionation increases electroluminescence emission at the same injection current and reduces nonradiative recombination. High-molecular-weight and fractionated IDTBT polymers exhibit higher carrier lifetime-mobility product compared to that of their nonfractionated analogues, resulting in improved solar cell performance. (Graph Presented). © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.5b05709
  • 2015 • 201 Ultrafiltration membranes with markedly different pH- and ion-responsivity by photografted zwitterionic polysulfobetain or polycarbobetain
    Birkner, M. and Ulbricht, M.
    Journal of Membrane Science 494 57-67 (2015)
    Stimuli-responsive ultrafiltration (UF) membranes were synthesized via photo-initiated "grafting from" of the zwitterionic monomers N-(3-sulfopropyl)-N-methacroyl-oxyethyl-N,N-dimethyl-ammonium betaine (sulfobetaine methacrylate, SPE) and 2-carboxy-N,N-dimethyl-N-(2'-(methacryl-oyloxy)ethyl)ethan-aminium inner salt (carbobetaine methacrylate, CBMA) onto commercial polyethersulfone UF membranes. The effects of kosmotropic and chaotropic potassium salts and pH on flux were determined in order to investigate the stimuli-responsive behavior of the polyzwitterion-grafted membranes. PolySPE showed the expected stimuli-responsiveness based on the "anti-polyelectrolyte" effect. The degree of swelling of grafted sulfobetaine polymer increased and water permeability decreased with increasing salt concentration; and the results can be related to the "Hofmeister series", i.e. the magnitude of the effect increased with increasing chaotropic character of the anion, in the order: SO<inf>4</inf>2-<H<inf>2</inf>PO<inf>4</inf>-<Cl-<ClO<inf>4</inf>-. However, the carbobetaine polymer (polyCBMA) did not show such anti-polyelectrolyte behavior at pH values in neutral and basic range. In contrast to the "strong-strong" type zwitterionic material polySPE, the swelling behavior of the "strong-weak" polyCBMA was significantly influenced by pH value because protonation of carboxylic acid side groups changes the grafted chains from net neutral zwitterionic into polycationic with ordinary polyelectrolyte properties. Hence, permeability of polyCBMA-grafted membranes increased with increasing salt concentration at pH=3. Furthermore, the rejection of dextrans as a function of electrolyte concentration and pH was determined and all results were in agreement with changes of water fluxes. For specific salt conditions, large and reversible changes of dextran rejection were found, confirming the possibilities of adjusting the sieving properties of the responsive zwitterionic membranes. Detailed studies by zetapotential measurements were also performed to investigate the specific effects of ion type, electrolyte concentration and pH onto the stimuli-responsive changes of surface charge of grafted membranes. All results support that the effects of the grafted zwitterionic polymers on the barrier properties of the UF membranes can be described with a pore-opening/-closing mechanism based on reversible deswelling/swelling of grafted chains on the pore walls in response to composition changes with respect to salt (for polySPE) or salt and pH value (polyCBMA). © 2015 Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2015.07.046
  • 2015 • 200 Controlling the charge of pH-responsive redox hydrogels by means of redox-silent biocatalytic processes. A biocatalytic off/on switch
    Contin, A. and Plumeré, N. and Schuhmann, W.
    Electrochemistry Communications 51 50-53 (2015)
    Coupling of redox-silent biocatalytic processes for analyte detection with enzyme-catalyzed redox reactions for signal generation is proposed by the modulation of electrostatic interactions between a pH-responsive polymer and a redox enzyme to control the off-on transition for electrochemical signal generation. Glassy carbon electrodes are modified with a poly(vinyl)imidazole Os(bipyridine)2Cl redox hydrogel film entrapping urease and PQQ-dependent glucose dehydrogenase, while glucose is present in the solution. The off-on transition is based on the detection of urea as model analyte which is hydrolyzed to ammonia by urease within the hydrogel film concomitantly increasing the local pH value thus invoking deprotonation of the imidazole groups at the polymer backbone. The decrease of positive charges at the polymer decreases electrostatic repulsion between the polymer and the positively charged PQQ-dependent glucose dehydrogenase. Hence, electron transfer rates between polymer-bound Os complexes and PQQ inside the enzyme are enhanced activating electrocatalytic oxidation of glucose. This process generates the electrochemical signal for urea detection. © 2014 Elsevier B.V.
    view abstractdoi: 10.1016/j.elecom.2014.12.001
  • 2015 • 199 Phenothiazine-functionalized redox polymers for a new cathode-active material
    Golriz, A.A. and Suga, T. and Nishide, H. and Berger, R. and Gutmann, J.S.
    RSC Advances 5 22947-22950 (2015)
    Redox-active, phenothiazine-functionalized polymers were synthesized and employed as a promising cathode-active material (∼3.7 V vs. Li, 77 Ah kg-1) in a rechargeable battery. The longer spacer between phenothiazine and the polymer backbone contributed to the stability of the formed radical cations, resulting in decelerated self-discharge and improved cycle performance. This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c4ra17107a
  • 2015 • 198 Micellization and Mobility of Amphiphilic Poly(2-oxazoline) Based Block Copolymers Characterized by 1H NMR Spectroscopy
    Hiller, W. and Engelhardt, N. and Kampmann, A.-L. and Degen, P. and Weberskirch, R.
    Macromolecules 48 4032-4045 (2015)
    Three amphiphilic diblock poly(2-oxazoline) copolymers composed of the hydrophilic poly(2-methyl-2-oxazoline) and hydrophobic poly(2-alkyl-2-oxazoline) with alkyl = pentyl (P1), heptyl (P2), and nonyl side chain (P3) lengths of the hydrophobic block were synthesized by ring-opening cationic polymerization. These polymers form micelles in water above their critical micelle concentration. The temperature-dependent stability of the micellar aggregates was analyzed by DLS and turbidity measurements as well as pyrene solubilization between 20 and 80 °C in water. Moreover, the chemical composition of the block copolymers was determined by 1H NMR spectroscopy. In particular, it was possible to quantify the degree of aggregations of the individual groups of both blocks by including the chemical composition into the derived equations. It could be shown by varying the temperature that both the chemical composition and the degree of micellization depend on the number of bonds of the considered structural groups of the side chain with respect to the backbone of the hydrophobic block as well as the length of the side chain. In addition, temperature-dependent T<inf>1</inf> and T<inf>2</inf> measurements were performed to determine the dynamics of the structural groups of the hydrophilic and hydrophobic blocks. Correlation times and activation energies were determined of the individual structural groups confirming the different mobilities. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.macromol.5b00149
  • 2015 • 197 Shape-memory PVDF exhibiting switchable piezoelectricity
    Hoeher, R. and Raidt, T. and Novak, N. and Katzenberg, F. and Tiller, J.C.
    Macromolecular Rapid Communications 36 2042-2046 (2015)
    In this study, a material is designed which combines the properties of shape-memory and electroactive polymers. This is achieved by covalent cross-linking of polyvinylidene fluoride. The resulting polymer network exhibits excellent shape-memory properties with a storable strain of 200%, and fixity as well as recovery values of 100%. Programming upon rolling induces the transformation from the nonelectroactive α-phase to the piezoelectric β-phase. The highest β-phase content is found to be 83% for a programming strain of 200% affording a d33 value of -30 pm V-1. This is in good accordance with literature known values for piezoelectric properties. Thermal triggering this material does not only result in a shape change but also renders the material nonelectroactive. Cross-linking of polyvinylidene fluoride results in a polymer network that combines excellent shape-memory properties with a switchable piezoelectricity. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/marc.201500410
  • 2015 • 196 Strategies for permanent immobilization of enzymes on textile carriers
    Kiehl, K. and Straube, T. and Opwis, K. and Gutmann, J.S.
    Engineering in Life Sciences 15 622-626 (2015)
    The economical use of expensive enzymes in chemical synthesis can be improved by the immobilization of the catalyst on a suitable support material. Textile fabrics made of polyester, polyamide, or cotton represent comparatively inexpensive alternative carrier materials in contrast to conventional supports. Textile-inherent advantages like its flexible and lightweight construction allow the use in reactors of arbitrary geometry, a quick separation from the reaction liquor, and the generation of residue-free product. A low preparative and economical expense is needed to prepare fabrics with high enzyme loads (20-70 mg enzyme/g textile carrier), high relative activity (up to 20%) and excellent permanence against enzyme desorption as well. In this study, we present different strategies for the covalent fixation of enzymes on fiber forming polymers such as photochemical grafting, the use of bifunctional anchor molecules, monomeric, and polymeric cross-linking agents or specific enzyme modification for direct immobilization. In addition, we compare the strategies in terms of load, catalytic activity, and reusability. All presented immobilization methods yield products, which exhibit a considerable activity even after twenty recycling steps. In conclusion, we have successfully identified textiles as alternative, new and promising low cost carrier materials for enzymes. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/elsc.201400148
  • 2015 • 195 Inverse analysis for heterogeneous materials and its application to viscoelastic curing polymers
    Klinge, S. and Steinmann, P.
    Computational Mechanics 55 603-615 (2015)
    This contribution aims at achieving two important goals: First, it outlines a numerical inverse homogenization strategy able to recover material parameters of the microstructure by using results of macroscopic tests. Second, it considers parameter identification for viscoelastic heterogeneous materials, which is a step providing the basis for the further extension toward the general treatment of dissipative processes. The approach proposed couples the Levenberg–Marquardt method with the multiscale finite element method. In this combination, the former is a gradient-based optimization strategy used to minimize a merit function while the latter is a numerical homogenization technique needed to solve the direct problem. The specific example studied in the paper deals with the investigation of a composite consisting of a viscoelastic curing polymer and a nonlinear elastic material. It proposes a three-step procedure for the evaluation of its material parameters and discusses the accuracy and the uniqueness of the solution. © 2015, Springer-Verlag Berlin Heidelberg.
    view abstractdoi: 10.1007/s00466-015-1126-5
  • 2015 • 194 Continuous delivery of rhBMP2 and rhVEGF165 at a certain ratio enhances bone formation in mandibular defects over the delivery of rhBMP2 alone - An experimental study in rats
    Lohse, N. and Moser, N. and Backhaus, S. and Annen, T. and Epple, M. and Schliephake, H.
    Journal of Controlled Release 220 201-209 (2015)
    The aim of the present study was to test the hypothesis that different amounts of vascular endothelial growth factor and bone morphogenic protein differentially affect bone formation when applied for repair of non-healing defects in the rat mandible. Porous composite PDLLA/CaCO3 carriers were fabricated as slow release carriers and loaded with rhBMP2 and rhVEGF165 in 10 different dosage combinations using gas foaming with supercritical carbon dioxide. They were implanted in non-healing defects of the mandibles of 132 adult Wistar rats with additional lateral augmentation. Bone formation was assessed both radiographically (bone volume) and by histomorphometry (bone density). The use of carriers with a ratio of delivery of VEGF/BMP between 0.7 and 1.2 was significantly related to the occurrence of significant increases in radiographic bone volume and/or histologic bone density compared to the use of carriers with a ratio of delivery of ≤ 0.5 when all intervals and all outcome parameters were considered. Moreover, simultaneous delivery at this ratio helped to "save" rhBMP2 as both bone volume and bone density after 13 weeks were reached/surpassed using half the dosage required for rhBMP2 alone. It is concluded, that the combined delivery of rhVEGF165 and rhBMP2 for repair of critical size mandibular defects can significantly enhance volume and density of bone formation over delivery of rhBMP2 alone. It appears from the present results that continuous simultaneous delivery of rhVEGF165 and rhBMP2 at a ratio of approximately 1 is favourable for the enhancement of bone formation. © 2015 Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.jconrel.2015.10.032
  • 2015 • 193 Synthesis and electrochromic properties of conducting polymers based on highly planar 2,7-disubstituted xanthene derivatives
    Olech, K. and Gutkowski, R. and Kuznetsov, V., Dr. and Roszak, S., Prof. Dr. and Sołoducho, J. and Schuhmann, W.
    ChemPlusChem 80 679-687 (2015)
    On the basis of preliminary DFT calculations, p-type semiconducting polymers based on 2,7-substituted xanthene building blocks that show a high degree of planarity were designed. The synthesis, electrochemical characterization, and theoretical modeling of 2,7-bis(thiophen-2-yl)-9,9-dimethylxanthene (1) and 2,7-bis(3-hexylthiophen-2-yl)-9,9-dimethylxanthene (2) is described. The synthetic procedure is based on the incorporation of thiophene rings by means of Pd-catalyzed cross-coupling reactions, which lead to monomers 1 and 2. Copolymers P1 and P2 obtained by means of anodic polymerization have been characterized by spectroscopic and electrochemical methods. Electrochromism was observed for both polymers. The experimental data supported by density functional theory modeling explain the influence of alkyl chain substitution on the properties of the investigated copolymers. Copyright © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cplu.201402349
  • 2015 • 192 Inhibition of interfacial oxidative degradation during SiOx plasma polymer barrier film deposition on model organic substrates
    Ozkaya, B. and Mitschker, F. and Ozcan, O. and Awakowicz, P. and Grundmeier, G.
    Plasma Processes and Polymers 12 392-397 (2015)
    Interfacial processes during the initial stages of SiO<inf>x</inf>-like plasma-polymer barrier coating deposition were investigated by means of polarization modulation infrared reflection-absorption spectroscopy, and the resulting effect on defect densities were studied by cyclic voltammetry. Octadecanethiol self-assembled monolayers on Au-film coated wafers served as sensor layers to investigate interface chemistry during the plasma deposition. Both the spectroscopic and electrochemical data revealed that a thin SiOCH interlayer could reduce oxidative degradation of the SAM during subsequent deposition of the SiO<inf>x</inf> barrier film from an oxygen-rich plasma phase. The present electrochemical investigation confirmed effective inhibition of interfacial oxidative degradation processes of an aliphatic polymer in the presence of a SiOCH interfacial layer. Interfacial processes during the initial stages of SiO<inf>x</inf>-like plasma barrier-coating deposition are investigated. Self-assembled monolayers on Au-film coated wafers serve as sensor layers. SiOCH-type organic interlayers are found to oxidize and reduce surface degradation processes upon subsequent barrier film deposition from oxygen-rich gas mixture. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/ppap.201400105
  • 2015 • 191 Soft Nanocomposites-From Interface Control to Interphase Formation
    Pihan, S.A. and Emmerling, S.G.J. and Butt, H.-J. and Berger, R. and Gutmann, J.S.
    ACS Applied Materials and Interfaces 7 12380-12386 (2015)
    We report measurements of structure, mechanical properties, glass transition temperature, and contact angle of a novel nanocomposite material consisting of swellable silsesquioxane nanoparticles with grafted poly(ethyl methacrylate) (PEMA) brushes and PEMA matrices with varying molecular weight. We measured the interparticle distance at the surface of the composites using scanning probe microscopy (SPM) and in the bulk of ∼0.5 μm thick films by grazing incidence small angle X-ray scattering (GISAXS). For a given molecular weight of the brush unstable dispersions at high molecular weight of the matrix indicate an intrinsic incompatibility between polymer-grafted-nanoparticles and homopolymer matrices. This incompatibility is affirmed by a high contact angle between the polymer-grafted-nanoparticles and the high molecular weight matrix as measured by SPM. For unstable dispersions, we measured a decreased glass transition temperature along with a decreased plateau modulus by dynamic mechanical thermal analysis (DMTA) which indicates the formation of a liquid-like layer at the brush-matrix interface. This proves the ability to decouple the structural and mechanical properties from the potential to be swollen with small molecules. It opens a new area of use of these soft nanocomposites as slow release materials with tailored mechanical properties. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/am507572q
  • 2015 • 190 Vegetable oil-based polybenzoxazine derivatives coatings on Zn-Mg-Al alloy coated steel
    Raicopol, M. and Bălănucă, B. and Sliozberg, K. and Schlüter, B. and Gârea, S.A. and Chira, N. and Schuhmann, W. and Andronescu, C.
    Corrosion Science 100 386-395 (2015)
    Based on environmentally friendly (bio-based) precursor materials a new class of benzoxazine derivatives was synthesized using phenolated high oleic sunflower oil as phenol component and either aniline or 1,6-diaminohexane as amine components. Hydrophobic and dense poly(benzoxazine) coatings on Zn-Mg-Al alloy coated steel were obtained after spin-coating or air-brush type spray coating by crosslinking during a heat treatment step. The poly(benzoxazine)-coated ZM-steel samples showed an anodic shift of the open circuit potential as well as the break-through potential. Using an automatic scanning droplet cell the impact of the polymer film thickness on corrosion protection was evaluated. © 2015 Elsevier Ltd.
    view abstractdoi: 10.1016/j.corsci.2015.08.018
  • 2015 • 189 Chemical cross-linking of polypropylenes towards new shape memory polymers
    Raidt, T. and Hoeher, R. and Katzenberg, F. and Tiller, J.C.
    Macromolecular Rapid Communications 36 744-749 (2015)
    In this work, syndiotactic polypropylene (sPP) as well as isotactic polypropylene (iPP) are cross-linked to gain a shape memory effect. Both prepared PP networks exhibit maximum strains of 700%, stored strains of up to 680%, and recoveries of nearly 100%. While x-iPP is stable for many cycles, x-sPP ruptures after the first shape-memory cycle. It is shown by wide-angle X-ray scattering (WAXS) experiments that cross-linked iPP exhibits homoepitaxy in the temporary, stretched shape but in contrast to previous reports it contains a higher amount of daughter than mother crystals. Shape memory polypropylene is prepared by cross-linking of syndiotactic as well as isotactic polypropylene (iPP). Cross-linked iPP is a shape-memory polymer with excellent stored strain, fixity-, and recovery-ratios. Wide angle X-ray scattering (WAXS) experiments reveal that the crystals in programmed x-iPP show a microstructure with mother and daughter crystals. In contrast to previous reports, the amount of daughter crystals exceeds that of the mothers. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/marc.201400727
  • 2015 • 188 Post-polymerization of urease-induced calcified, polymer hydrogels
    Rauner, N. and Buenger, L. and Schuller, S. and Tiller, J.C.
    Macromolecular Rapid Communications 36 224-230 (2015)
    Urease-induced calcification is an innovative method to artificially produce highly filled CaCO3-based composite materials by intrinsic mineralization of hydrogels. The mechanical properties of these hybrid materials based on poly(2-hydroxyethylacrylate) cross-linked by triethylene glycol dimethacrylate are poor. Increasing the degree of calcification to up to 94 wt% improves the Young's moduli (YM) of the materials from some 40 MPa to more than 300 MPa. The introduction of calcium carbonate affine groups to the hydrogel matrix by copolymerizing acrylic acid and [2-(methacryloyloxy) ethyl]trimethylammonium chloride, respectively, does not increase the stiffness of the composites. A Young's modulus of more than 1 GPa is achieved by post-polymerization (PP) of the calcified hydrogels, which proves that the size of the contact area between the matrix and calcium carbonate crystals is the most crucial parameter for controlling the stiffness of hybrid materials. Switching from low Tg to high Tg hydrogel matrices (based on poly(N,N-dimethyl acrylamide)) results in a YM of up to 3.5 GPa after PP. (Chemical Equation Presented). © 2014 Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/marc.201400426
  • 2015 • 187 Modeling aqueous two-phase systems: III. Polymers and organic salts as ATPS former
    Reschke, T. and Brandenbusch, C. and Sadowski, G.
    Fluid Phase Equilibria 387 178-189 (2015)
    In this work the electrolyte perturbed chain statistical associating fluid theory (ePC-SAFT) is applied to model aqueous two-phase systems (ATPS) containing one of 6 different polymers and one of 8 different organic salts at temperatures between 278.15. K and 313.15. K. To accurately model the thermodynamic properties of organic-salt solutions, a novel modeling approach was applied, which accounts for the non-spherical shape of the anions. Applying this approach, 14 organic salt solutions have been modeled with an overall average relative deviation of 0.23% for solution densities and 1.51% for osmotic coefficients. The modeling of the polymers (PEG, PEGDME, PPG, and poly(ethylene glycol-. co-propylene glycol)) has been carried out using a copolymer approach accounting for different molecular interactions of the polymer segments. Applying this approach, ATPS containing polymers and organic salts were modeled accurately. The overall absolute average deviation of the modeling with respect to the concentrations of the phase-forming components was 2.10. wt%. The influence of polymer molecular weight, polymer composition, kind of salt, pH, and temperature on the equilibrium composition and densities of the two phases was modeled correctly with ePC-SAFT. Moreover, it is shown that by applying ion-specific model parameters, ePC-SAFT is even capable of predicting ATPS containing salts which were not used for the parameter estimation. © 2014 Elsevier B.V..
    view abstractdoi: 10.1016/j.fluid.2014.12.011
  • 2015 • 186 Bipyridine-functionalized amphiphilic block copolymers as support materials for the aerobic oxidation of primary alcohols in aqueous media
    Sand, H. and Weberskirch, R.
    RSC Advances 5 38235-38242 (2015)
    Amphiphilic block copolymers with 4-methoxy-4′-alkoxybipyridine ligands in the hydrophobic block were synthesized by cationic ring-opening polymerization. The bipyridine moiety was either introduced directly as a 2-oxazoline monomer (P1) or by polymer-analogous coupling to a precursor poly(2-oxazoline) with chloropentyl side chains (PP2-PP7) to prepare the polymer ligands (P2-P7). The polymers were characterized by NMR and SEC measurements to determine polymer composition, molar masses and polydispersities. In water, these polymers form micelles with cmc values ranging from 1.8 to 22 μmol l-1. SAXS and DLS measurements exhibited spherical particles with particle sizes of 8 to 21 nm. Polymers P1-P7 were finally utilized to carry out the aerobic oxidation of primary alcohols, including allylic, benzylic, and aliphatic derivatives at room temperature (T = 20°C) and ambient air in aqueous media indicating higher activities for P2-P7 compared to P1 as a consequence of the different preparation methods. Moreover, product isolation and catalyst recycling can be easily accomplished by solvent extraction five times without significant loss of activity. © The Royal Society of Chemistry 2015.
    view abstractdoi: 10.1039/c5ra05715a
  • 2015 • 185 Electropolymerized molecularly imprinted polypyrrole film for sensing of clofibric acid
    Schweiger, B. and Kim, J. and Kim, Y.J. and Ulbricht, M.
    Sensors (Switzerland) 15 5870-5889 (2015)
    Piezoelectric quartz crystals and analogous gold substrates were electrochemically coated with molecularly imprinted polypyrrole films for pulsed amperometric detection (PAD) of clofibric acid, a metabolite of clofibrate. Cyclic voltammetry data obtained during polymerization and deposited weight estimations revealed a decrease of the polymerization rate with increasing clofibric acid concentration. XPS measurements indicated that clofibric acid could be removed after imprinting with an aqueous ethanol solution, which was further optimized by using PAD. Zeta potential and contact angle measurements revealed differences between molecularly imprinted (MIP) and non-imprinted polymer (NIP) layers. Binding experiments with clofibric acid and other substances showed a pronounced selectivity of the MIP for clofibric acid vs. carbamazepine, but the response of MIP and NIP to 2,4-dichlorophenoxyacetic acid was higher than that for clofibric acid. A smooth surface, revealed by AFM measurements, with roughness of 6–8 nm for imprinted and non-imprinted layers, might be a reason for an excessively low density of specific binding sites for clofibric acid. Furthermore, the decreased polymerization rate in the presence of clofibric acid might not result in well-defined polymer structures, which could be the reason for the lower sensitivity. © 2015 by the authors; licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/s150304870
  • 2015 • 184 Nontoxic, Hydrophilic Cationic Polymers - Identified as Class of Antimicrobial Polymers
    Strassburg, A. and Kracke, F. and Wenners, J. and Jemeljanova, A. and Kuepper, J. and Petersen, H. and Tiller, J.C.
    Macromolecular Bioscience 15 1710-1723 (2015)
    Amphiphilic polycations are an alternative to biocides but also toxic to mammalian cells. Antimicrobially active hydrophilic polycations based on 1,4-dibromo-2-butene and tetramethyl-1,3-propanediamine named PBI are not hemotoxic for porcine red blood cells with a hemocytotoxicity (HC50) of more than 40 000 μg · mL-1. They are quickly killing bacterial cells at their MIC (minimal inhibitory concentration). The highest found selectivity HC50/MIC is more than 20 000 for S. epidermidis. Investigations on sequentially prepared PBIs with defined molecular weight Mn and tailored end groups revealed that there is a dependence of antimicrobial activity and selectivity on Mn and nature of the end groups. Antimicrobially active and nontoxic hydrophilic polycations based on 1,4-dibromo-2-butene and tetramethyl-1,3-propanediamine (PBI) are an alternative to toxic biocides and amphiphilic polycations. Investigations on PBIs with defined molecular weight (Mn) and tailored end groups revealed that there is a dependence of antimicrobial activity and selectivity on Mn and nature of the end groups. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/mabi.201500207
  • 2015 • 183 Poly(N,N-dimethylaminoethyl methacrylate) Brushes: PH-Dependent Switching Kinetics of a Surface-Grafted Thermoresponsive Polyelectrolyte
    Thomas, M. and Gajda, M. and Amiri Naini, C. and Franzka, S. and Ulbricht, M. and Hartmann, N.
    Langmuir 31 13426-13432 (2015)
    The temperature-dependent switching behavior of poly(N,N-dimethylaminoethyl methacrylate) brushes in alkaline, neutral, and acidic solutions is examined. A novel microscopic laser temperature-jump technique is employed in order to study characteristic thermodynamic and kinetic parameters. Static laser micromanipulation experiments allow one to determine the temperature-dependent variation of the swelling ratio. The data reveal a strong shift of the volume phase transition of the polymer brushes to higher temperatures when going from pH = 10 to pH = 4. Dynamic laser micromanipulation experiments offer a temporal resolution on a submillisecond time scale and provide a means to determine the intrinsic rate constants. Both the swelling and the deswelling rates strongly decrease in acidic solutions. Complementary experiments using in situ atomic force microscopy show an increased polymer layer thickness at these conditions. The data are discussed on the basis of pH-dependent structural changes of the polymer brushes including protonation of the amine groups and conformational rearrangements. Generally, repulsive electrostatic interactions and steric effects are assumed to hamper and slow down temperature-induced switching in acidic solutions. This imposes significant restrictions for smart polymer surfaces, sensors, and devices requiring fast response times. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.5b03448
  • 2015 • 182 Thermal conductivity of advanced TiC reinforced metal matrix composites for polymer processing applications
    Wilzer, J. and Windmann, M. and Weber, S. and Hill, H. and Bennekom, A.V. and Theisen, W.
    Journal of Composite Materials 49 243-250 (2015)
    Tools used for fabricating polymers are often required to have low thermal conductivities, e.g. for pelletizing, because this lowers the risk of the polymer nozzle being obstructed by molten polymer solidifying as it exits. Latterly, advanced corrosion and wear resistant metal matrix composites (MMCs) are used for pelletizing tools. Therefore, with respect to polymer processing it is important to know how the thermal conductivity of MMC gets influenced by hard phase and metal matrix contribution. In this study, the thermal conductivity of a TiC reinforced corrosion and wear resistant MMC gets analyzed. Especially the influence of chemical interdiffusion between TiC and metal matrix on the resulting thermal conductivity gets analyzed. It is shown that changes in the chemical composition lead to distinct decrease in thermal conductivity of the TiC which has to be considered when MMC thermal conductivities have to be examined. © The Author(s) 2013 Reprints and permissions:
    view abstractdoi: 10.1177/0021998313516143
  • 2015 • 181 Light Induced H2 Evolution from a Biophotocathode Based on Photosystem 1 - Pt Nanoparticles Complexes Integrated in Solvated Redox Polymers Films
    Zhao, F. and Conzuelo, F. and Hartmann, V. and Li, H. and Nowaczyk, M.M. and Plumeré, N. and Rögner, M. and Schuhmann, W.
    Journal of Physical Chemistry B 119 13726-13731 (2015)
    We report on a biophotocathode based on photosystem 1 (PS1)-Pt nanoparticle complexes integrated in a redox hydrogel for photoelectrocatalytic H2 evolution at low overpotential. A poly(vinyl)imidazole Os(bispyridine)2Cl polymer serves as conducting matrix to shuttle the electrons from the electrode to the PS1-Pt complexes embedded within the hydrogel. Light induced charge separation at the PS1-Pt complexes results in the generation of photocurrents (4.8 ± 0.4 μA cm-2) when the biophotocathodes are exposed to anaerobic buffer solutions. Under these conditions, the protons are the sole possible electron acceptors, suggesting that the photocurrent generation is associated with H2 evolution. Direct evidence for the latter process is provided by monitoring the H2 production with a Pt microelectrode in scanning electrochemical microscopy configuration over the redox hydrogel film containing the PS1-Pt complexes under illumination. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcb.5b03511
  • 2015 • 180 Feature-based tensor field visualization for fiber reinforced polymers
    Zobel, V. and Stommel, M. and Scheuermann, G.
    2015 IEEE Scientific Visualization Conference, SciVis 2015 - Proceedings 49-56 (2015)
    Virtual testing is an integral part of modern product development in mechanical engineering. Numerical structure simulations allow the computation of local stresses which are given as tensor fields. For homogeneous materials, the tensor information is usually reduced to a scalar field like the von Mises stress. A material-dependent threshold defines the material failure answering the key question of engineers. This leads to a rather simple feature-based visualisation. For composite materials like short fiber reinforced polymers, the situation is much more complex. The material property is determined by the fiber distribution at every position, often described as fiber orientation tensor field. Essentially, the material's ability to cope with stress becomes anisotropic and inhomogeneous. We show how to combine the stress field and the fiber orientation field in such cases, leading to a feature-based visualization of tensor fields for composite materials. The resulting features inform the engineer about potential improvements in the product development. © 2015 IEEE.
    view abstractdoi: 10.1109/SciVis.2015.7429491
  • 2014 • 179 Plastic flow and failure in single point incremental forming of PVC sheets
    Alkas Yonan, S. and Silva, M.B. and Martins, P.A.F. and Tekkaya, A.E.
    Express Polymer Letters 8 301-311 (2014)
    This paper presents an innovative and effective methodology to characterize plastic flow and failure in single point incremental forming (SPIF) of polymers that allows determining the stresses and the accumulated values of ductile damage directly from the experimental values of strain at various positions over the deformed polymer sheets. The approach traces the deformation path of material elements in conical and pyramidal SPIF parts, undergoing linear strain loading paths from beginning until failure, and is built upon the generalization of the analytical framework conditions assumed by Glover et al. [1] to the pressure-sensitive yield surfaces of polymers under incompressible, non-associated, plastic flow. Experimentation in conventional and multi-stage SPIF of Polyvinylchloride (PVC) sheets confirms the effectiveness of the proposed methodology and demonstrates that standard non-coupled damage models currently utilized in sheet metal forming are inapplicable to describe failure in polymers. Instead fracture forming limit lines (FFL's) should be employed. © BME-PT.
    view abstractdoi: 10.3144/expresspolymlett.2014.34
  • 2014 • 178 Thermodynamic model for polyelectrolyte hydrogels
    Arndt, M.C. and Sadowski, G.
    Journal of Physical Chemistry B 118 10534-10542 (2014)
    The composition and swelling behavior of hydrogels may be dramatically influenced by external stimuli. Polyelectrolyte hydrogels consisting of charged polymers are particularly well-known for a high sensitivity to the presence of ionic species. For a thermodynamic description of such systems, the polyelectrolyte Perturbed-Chain Statistical Association Fluid Theory (pePC-SAFT) equation of state was augmented and merged with an extension of the modeling of hydrogels. This combined approach allowed for two effects to be taken into account: first, charges along the polymer chain and their interaction with mobile ions of the same or opposite charge in aqueous solutions and, second, the elastic interactions of swellable networks and their effect on Helmholtz energy and pressure. Thus, predictions of the degree of counterion condensation on the polymer chains could be made both for vapor-liquid equilibria of aqueous polyelectrolyte solutions and for polyelectrolyte hydrogels in aqueous salt solutions. The influence of temperature and molecular weight thereon was predicted successfully, and the impact of the degree of neutralization and the effect of additional salts were examined in comparison to literature data. With the inclusion of the influence of the Donnan potential, our model gave good predictions of swellable polyelectrolyte hydrogel systems in salt solutions. Poly(acrylic acid) and poly(methacrylic acid) gels were studied along with their corresponding sodium salts. Their swelling behavior in aqueous NaCl and NaNO3 solutions was examined. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/jp501798x
  • 2014 • 177 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 abstractdoi: 10.1080/09205063.2014.929429
  • 2014 • 176 Adhesion of thin CVD films on pulsed plasma pre-treated polypropylene
    Behm, H. and Bahroun, K. and Bahre, H. and Kirchheim, D. and Mitschker, F. and Bibinov, N. and Böke, M. and Dahlmann, R. and Awakowicz, P. and Hopmann, C. and Winter, J.
    Plasma Processes and Polymers 11 418-425 (2014)
    The adhesion of thin CVD films on polyolefins is often critical due to the low surface free energy of the polymers. In this study, injection moulded PP samples are produced and investigated. The samples are treated in very well-characterized pulsed plasmas before a HMDSO-based coating is applied. The resulting bond strength is analyzed using pull-off tests. The fractured interfaces are characterized with XPS. Oxygen and argon plasma pre-treatments of the PP samples result in a bond strength improvement by a factor of about 2. Comparing oxygen and argon pre-treatments at equal ion fluences to the surface, it can be shown that the bond strength between CVD-coating and polymer is similar. The influence of well-defined argon and oxygen pre-treatment plasmas on the adhesion of silicon organic CVD films (SiOCH) on polypropylene (PP) is investigated. Very short pre-treatment times result in an increase in bond strength by a factor of 2. Measurements show a dependency of the ion fluence on the surface on the bond strength between CVD film and PP in the region of best adhesion. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/ppap.201300128
  • 2014 • 175 Bi-Zn bond formation in liquid ammonia solution: [Bi-Zn-Bi]4-, a linear polyanion that is Iso(valence)-electronic to CO2
    Benda, C.B. and Köchner, T. and Schäper, R. and Schulz, S. and Fässler, T.F.
    Angewandte Chemie - International Edition 53 8944-8948 (2014)
    Reactions of the zinc(I) complex [Zn2(Mesnacnac)2] (Mesnacnac=[(2,4,6-Me3C6H2)NC(Me)] 2CH) with solid K3Bi2 dissolved in liquid ammonia yield crystals of the compound K4[ZnBi2] ·(NH3)12 (1), which contains the molecular, linear heteroatomic [Bi-Zn-Bi]4- polyanion (1a). This anion represents the first example of a three-atomic molecular ion of metal atoms being iso(valence)-electronic to CO2 and being synthesized in solution. The analogy of the discrete [Bi-Zn-Bi]4- anion and the polymeric 1 ∞ [(ZnBi4/2)4-] unit to monomeric CO2 and polymeric SiS2 is rationalized. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201404343
  • 2014 • 174 Optimization of thermomechanical processes for the functional gradation of polymers by means of advanced empirical modeling techniques
    Biermann, D. and Hess, S. and Ries, A. and Wagner, T. and Wibbeke, A.
    AIP Conference Proceedings 1593 766-770 (2014)
    I In this paper, an optimization procedure for complex manufacturing processes is presented. The procedure is based on advanced empirical modeling techniques and will be presented in two parts. The first part comprises the selection and generation of the empirical surrogate models. The process organization and the design of experiments are taken into account. In order to analyze and optimize the processes based on the empirical models, advanced methods and tools are presented in the second part. These tools include visualization methods and a sensitivity and robustness analysis. Moreover, the obtained surrogate models are used for a model-based multi-objective optimization in order to explore the gradation potential of the processes. The procedure is applied to two thermo-mechanical processes for the functional gradation of polymers - a monoxiale stretching of polycarbonate films and a compression moulding process for polypropylene sheets. © 2014 American Institute of Physics.
    view abstractdoi: 10.1063/1.4873888
  • 2014 • 173 PQQ-sGDH bioelectrodes based on os-complex modified electrodeposition polymers and carbon nanotubes
    Chen, X. and Shao, M. and Pöller, S. and Guschin, D. and Pinyou, P. and Schuhmann, W.
    Journal of the Electrochemical Society 161 H3058-H3063 (2014)
    Graphite electrodes were modified with specifically designed Os-complex modified electrodeposition polymers exhibiting a formal potential of the polymer-bound complex of about 0 to 20 mV (vs. Ag/AgCl/3MKCl) which is only about 100 mV anodic of the formal potential of pyrroloquinoline quinone (PQQ) in PQQ-dependent glucose dehydrogenase (PQQ-GDH). The efficiency of wiring the polymer-entrapped PQQ-GDH was dependent on the nature of the polymer backbone, the crosslinking with bifunctional crosslinkers and the co-entrapment of multi-walled carbon nanotubes. Due to the limited long-term stability a new polymer synthesis strategy was adapted using the same Os-complex but providing enhanced crosslinking capabilities by introducing epoxide functions at the polymer backbone. Related bioelectrodes showed enhanced glucose-dependent current and a stability of at least 3 days of continuous operation. © The Author(s) 2014.
    view abstractdoi: 10.1149/2.0111413jes
  • 2014 • 172 Modelling polylactide/water/dioxane systems for TIPS scaffold fabrication
    Cocchi, G. and Angelis, M.G.D. and Sadowski, G. and Doghieri, F.
    Fluid Phase Equilibria 374 1-8 (2014)
    The representation of liquid-liquid equilibria (LLE) in ternary systems composed by water, 1,4-dioxane and different grades of poly(lactic acid) (PDLLA and PLLA), has been addressed through the PC-SAFT equation of state (EoS), in which the scheme of induced association is used to represent the interaction between solvent (dioxane) and non-solvent (water). The model parameters devoted to the description of pure component properties, as well as those pertinent to the representation of thermodynamic behaviour of solvent/non-solvent mixtures, were tuned on the basis of specific pressure-volume-temperature (PVT) data for the corresponding systems. Only the binary parameters for polymer-solvent and polymer/non-solvent pairs were adjusted to obtain a useful representation of experimental LLE data for the ternary systems. A suitable description of the thermodynamic properties of ternary mixtures was obtained using temperature-independent binary interaction parameters in the range 25-80. °C, and the consistency of the approach in the entire composition range was verified against experimental solubility data specifically measured for the polymer/non-solvent pair. The model shows good ability in the description of the thermodynamic properties of the system and it represents a reliable tool for the prediction of LLE also at conditions different from those considered for its set-up. This approach thus represents a useful designing tool for processes, such as thermally induced phase separation (TIPS), used in the preparation of microporous polymeric scaffolds. © 2014 Elsevier B.V.
    view abstractdoi: 10.1016/j.fluid.2014.04.007
  • 2014 • 171 Configurational forces for quasi-incompressible large strain electro-viscoelasticity - Application to fracture mechanics
    Denzer, R. and Menzel, A.
    European Journal of Mechanics, A/Solids 48 3-15 (2014)
    This work treats theoretical and numerical aspects of configurational forces with application to fracture mechanics of electroactive polymers (EAPs) modelled in the continuum mechanics based context of large strain quasi-incompressible electro-viscoelasticity. We adopt a four-field formulation to take the quasi-incompressible behaviour in a finite element framework into account. We discuss the numerical implementation of viscosity-related evolution equations and the implications of viscous internal variables on the computation of configurational forces. As numerical examples for time depending crack driving forces we discuss a pre-cracked stacked EAP actuator as well as a pre-cracked and pre-stretched block actuator. © 2014 Elsevier Masson SAS. All rights reserved.
    view abstractdoi: 10.1016/j.euromechsol.2014.05.012
  • 2014 • 170 Synthesis of α,ω-isocyanate telechelic polymethacrylate soft segments with activated ester side functionalities and their use for polyurethane synthesis
    Eschweiler, N. and Keul, H. and Millaruelo, M. and Weberskirch, R. and Moeller, M.
    Polymer International 63 114-126 (2014)
    Isocyanate homo telechelic poly(methyl methacrylate-co-acryloxy succinimide) and poly(methyl methacrylate-co-acrylamidohexanoic succinimide) were prepared and used as soft segments for polyurethanes. Polymer structures are characterized by SEC, Raman, and 1H NMR spectroscopy. The synthetic route for the preparation of α,ω-isocyanate-telechelic poly(methyl methacrylate-co-acryloxysuccinimide) and α,ω- isocyanate-telechelic poly(methyl methacrylate-co-acrylamidohexanoic succinimide) soft segments is presented. The strategy includes reversible addition fragmentation chain transfer (RAFT) copolymerization and two post polymerization modification steps. The RAFT polymerizations result in copolymers with an activated ester proportion within the polymer chains of 8% N-acryloxysuccinimide and 5% 6-acrylamidohexanoic succinimide. The reactivity ratios of the monomer pairs were determined. In a first post polymerization reaction carboxylic acid homo telechelic polymers were prepared by reacting the ω-dithiobenzoate end-group with an excess of azobis(cyanovaleric acid). In a second modification step the α- and ω-carboxylic acid end-groups were reacted with hexamethylene diisocyanate and 100% isocyanate telechelic copolymers were obtained. Finally segmented polyurethanes were prepared by coupling hexamethylene diisocyanate (HDI) end capped soft segments with hard segments composed of 1,4-butanediol and HDI. © 2013 Society of Chemical Industry.
    view abstractdoi: 10.1002/pi.4535
  • 2014 • 169 Block copolymer photo-grafted poly(ethylene terephthalate) capillary pore membranes distinctly switchable by two different stimuli
    Geismann, C. and Tomicki, F. and Ulbricht, M.
    Separation Science and Technology (Philadelphia) 44 3312-3329 (2014)
    Track-etched poly(ethylene terephthalate) capillary pore membranes with a pore diameter of 690 nm were functionalized via photo-initiated “living” radical graft polymerization with block copolymers of acrylic acid and N-isopropylacrylamide. Preadsorbed xanthone was more efficient than benzophenone in order to achieve higher grafting efficiency and “living” character, including the option to reinitiate a grafted homopolymer to obtain grafted diblock copolymers. Characterizations were mainly done with water flux and dextran diffusion experiments at temperatures below and above the lower critical solution temperature (32°C) of poly(N-isopropylacrylamide) and pH values below and above the pKa value (4.5) of poly(acrylic acid). Block sequences and relative block lengths were identified to obtain stimuli-responsive membranes which have no measurable water flux and allow only low dextran diffusion rates at 25°C and pH 7 (“closed state”), and which reversibly open their pores by either increase of temperature or decrease of pH, or by the combination of both stimuli. © Taylor & Francis Group, LLC.
    view abstractdoi: 10.1080/01496390903212755
  • 2014 • 168 Inline quality prognosis of material condition induced process variations
    Heinzler, F.A. and Wortberg, J.
    AIP Conference Proceedings 1593 163-169 (2014)
    The main variation in a good quality production are induced by material condition. Processing technical polymers like PA, ABS or PBT possible influences are residual moisture conditions of the material or minor variations of raw material charges. Small changes in the material properties are difficult to detect at first quality controls and can be within the property tolerances. But even these small differences cause defects. The effects range from viscosity variations to varied crystalline properties. The influence of material properties on the processing have to be detected inline and combined with material analysis to a quality prognosis. The equipped sensors at injection molding machines enable an adequate process performance. The recently available solutions for power consumption monitoring enhance the available process control opportunities. Because of the high process speed of injection molding machines, the required sampling rate has to be minimal 500 Hz. A setup of high bandwidth data processing linked to the machine control enables precise characterization of the production. Identified index numbers, energetic data and characteristic development of measured process figures enable a high resolution detection of material induced variations. This prognosis enables inline classification of the produced parts and a compensation by correlating quality requirements with adjusted filling and packing parameters. © 2014 American Institute of Physics.
    view abstractdoi: 10.1063/1.4873756
  • 2014 • 167 A hypothetical model based on effectiveness of combined alkali and polymer latex modified jute fibre in controlling the setting and hydration behaviour of cement
    Jo, B.-W. and Chakraborty, S. and Yoon, K.W.
    Construction and Building Materials 68 1-9 (2014)
    Present investigation deals with the effectiveness of combined dilute alkali and polymer modified jute in controlling the setting and hydration behaviour of cement. Modification of jute fibre by combined alkali and polymer emulsion is a selective pathway to recover the delayed setting and hydration behaviour of jute cement paste. Setting time measurement, hydration test, free lime content estimation, SEM and FTIR were the selective choice to evaluate the targeted importance. Based on these analyses a model has been proposed to explain the hydration delaying effect of jute is recovered by the application of appropriate polymer content (0.0513%) in emulsion. © 2014 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.conbuildmat.2014.06.043
  • 2014 • 166 3D-CFD-simulation of melting processes in a high-speed-extruder with solid-melt-separation
    Karrenberg, G. and Wortberg, J.
    AIP Conference Proceedings 1593 623-627 (2014)
    This paper deals with the development of the so called High-Speed-S-Truder. The alternative extrusion concept uses a special plastification sleeve with hundreds of bores surrounding the screw to separate the emerging melt from solid material in the screw channel. To analyze and improve the complex fluid flow in this process CFD-simulations are used. However, the ability of simulating the flow as well as the plastification process is yet not given in any CFD-software. Thus an approach for 3D-CFDsimulations of melting polymeric materials in extrusion processes has been developed. A new material model enables to differ between solid phase and fluid phase in dependence of temperature in just one set of property descriptions. Hence it becomes possible to simulate melting in a single fluid domain without presupposing any melting mechanism. Therefore the model is universally applicable and can be used for the simulation of ordinary extrusion processes under high speed conditions as well as for the investigation and improvement of the melting mechanism in the High-Speed-S-Truder. © 2014 American Institute of Physics.
    view abstractdoi: 10.1063/1.4873857
  • 2014 • 165 Antimicrobial poly(2-methyloxazoline)s with bioswitchable activity through satellite group modification
    Krumm, C. and Harmuth, S. and Hijazi, M. and Neugebauer, B. and Kampmann, A.-L. and Geltenpoth, H. and Sickmann, A. and Tiller, J.C.
    Angewandte Chemie - International Edition 53 3830-3834 (2014)
    Biocides are widely used for preventing the spread of microbial infections and fouling of materials. Since their use can build up microbial resistance and cause unpredictable long-term environmental problems, new biocidal agents are required. In this study, we demonstrate a concept in which an antimicrobial polymer is deactivated by the cleavage of a single group. Following the satellite group approach, a biocidal quaternary ammonium group was linked through a poly(2-methyloxazoline) to an ester satellite group. The polymer with an octyl-3-propionoate satellite group shows very good antimicrobial activity against Gram-positive bacterial strains. The biocidal polymer was also found to have low hemotoxicity, resulting in a high HC50/MIC value of 120 for S. aureus. Cleaving the ester satellite group resulted in a 30-fold decrease in antimicrobial activity, proving the concept valid. The satellite group could also be cleaved by lipase showing that the antimicrobial activity of the new biocidal polymers is indeed bioswitchable. Biocides are widely used for preventing the spread of microbial infections and the fouling of materials. Since their application can build up microbial resistance and cause unpredictable long-term environmental problems, new biocidal agents are required. In a novel approach an antimicrobial polymer is deactivated by hydrolysis of an ester group through the action of a lipase. The crucial feature is the mutual interaction of the two endgroups of the polymer. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201311150
  • 2014 • 164 Affinity polymers tailored for the protein A binding site of immunoglobulin G proteins
    Latza, P. and Gilles, P. and Schaller, T. and Schrader, T.
    Chemistry - A European Journal 20 11479-11487 (2014)
    Rational design in combination with a screening process was used to develop affinity polymers for a specific binding site on the surface of immunoglobulin G (IgG) proteins. The concept starts with the identification of critical amino acid residues on the protein interface and their topological arrangement. Appropriate binding monomers were subsequently synthesized. Together with a sugar monomer (2-5 equiv) for water solubility and a dansyl monomer (0.5 equiv) as a fluorescent label, they were subjected in aqueous solution to linear radical copolymerization in various compositions (e.g., azobisisobutyronitrile (AIBN), homogeneous water/DMF mixtures). After ultrafiltration and lyophilization, colorless dry water-soluble powders were obtained. NMR spectroscopic and gel permeation chromatography (GPC) characterization indicated molecular weights between 30 and 500 kD and confirmed retention of monomer composition as well as the absence of monomers. In a competitive enzyme-linked immunosorbent assay (ELISA) screen of the polymer libraries (20-50 members), few copolymers qualified as strong and selective binders for the protein A binding site on the Fc fragment of the antibody. Their monomer composition precisely reflected the critical amino acids found at the interface. The simple combination of a charged and a nonpolar binding monomer sufficed for selective submicromolar IgG recognition by the synthetic polymer. Affinities were confirmed by fluorescence titrations; they increased with decreasing salt load but remained largely unaltered at lowered pH. Other proteins, including those of similar size and isoelectric point (pI), were bound 10-1000 times less tightly. This example indicates that interaction domains in other proteins may also be targeted by synthetic polymers if their comonomer composition reflects the nature and arrangement of amino acid residues on the protein surface. Some like it hot: Designed affinity polymers recognize the hot spot on a protein surface by virtue of their carefully selected binding monomers. Here, it is the protein A binding site on the Fc fragment of immunoglobulin G proteins (see figure), which is essential for medicinal antibody purification. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/chem.201402399
  • 2014 • 163 Hot-melt extruded drug-loaded rods: Evaluation of the mechanical properties for individual dosing via the Solid Dosage Pen
    Laukamp, E.J. and Thommes, M. and Breitkreutz, J.
    International Journal of Pharmaceutics 475 344-350 (2014)
    Individual dosing of peroral medicines is important for personalised medicine and patient-centred treatment, e.g., of children and the elderly. The Solid Dosage Pen (SDP) offers the opportunity to dose individually by cutting drug-loaded rods into tablet-like slices. The aim of the present study is the systematic evaluation of the mechanical properties of these drug-loaded rods prepared via hot-melt extrusion. The drug-loaded rods contain carbamazepine as a model drug, and polyethylene glycols and poloxamers as excipients. For the evaluation of the mechanical properties of the extrudates, three parameters were considered: tensile strength, E-modulus, and maximum cutting force. To examine the practicability of the device and the formulations for patient-centred treatment, the needed cutting forces were compared to literature data of the manual forces of different age groups. The maximum cutting force and the tensile strength were marginally changed over a storage period of six months (21 ± 0.2 °C, 45% r.H). A tensile strength below 9.1 ± 0.3 MPa and an E-modulus below 135.9 ± 7.2 MPa were found to be valuable thresholds for the applicability by the Solid Dosage Pen. Formulations containing PEG 1500 as additive fulfilled the pharmacopeial requirements containing the content uniformity even for the smallest dose. © 2014 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.ijpharm.2014.09.001
  • 2014 • 162 Hidden structural features of multicompartment micelles revealed by cryogenic transmission electron tomography
    Löbling, T.I. and Haataja, J.S. and Synatschke, C.V. and Schacher, F.H. and Müller, M. and Hanisch, A. and Gröschel, A.H. and Müller, A.H.E.
    ACS Nano 8 11330-11340 (2014)
    The demand for ever more complex nanostructures in materials and soft matter nanoscience also requires sophisticated characterization tools for reliable visualization and interpretation of internal morphological features. Here, we address both aspects and present synthetic concepts for the compartmentalization of nanoparticle peripheries as well as their in situ tomographic characterization. We first form negatively charged spherical multicompartment micelles from ampholytic triblock terpolymers in aqueous media, followed by interpolyelectrolyte complex (IPEC) formation of the anionic corona with bis-hydrophilic cationic/neutral diblock copolymers. At a 1:1 stoichiometric ratio of anionic and cationic charges, the so-formed IPECs are charge neutral and thus phase separate from solution (water). The high chain density of the ionic grafts provides steric stabilization through the neutral PEO corona of the grafted diblock copolymer and suppresses collapse of the IPEC; instead, the dense grafting results in defined nanodomains oriented perpendicular to the micellar core. We analyze the 3D arrangements of the complex and purely organic compartments, in situ, by means of cryogenic transmission electron microscopy (cryo-TEM) and tomography (cryo-ET). We study the effect of block lengths of the cationic and nonionic block on IPEC morphology, and while 2D cryo-TEM projections suggest similar morphologies, cryo-ET and computational 3D reconstruction reveal otherwise hidden structural features, e.g., planar IPEC brushes emanating from the micellar core. (Figure Presented). © 2014 American Chemical Society.
    view abstractdoi: 10.1021/nn504197y
  • 2014 • 161 Molecular dynamics studies of poly(N-isopropylacrylamide) endgrafted on the surfaces of model slab pores
    Lorbeer, L. and Alaghemandi, M. and Spohr, E.
    Journal of Molecular Liquids 189 57-62 (2014)
    We report first results of a systematic study of the properties of thermo-responsive polymer chains of poly(N-isopropylacrylamide) (PNIPAM), which are endgrafted onto the inner surfaces of a slab pore of approximately 9 nm width. We have systematically varied the strength of the PNIPAM-surface interaction energy to estimate the variation of the extent of the thermo-responsive effect on different surfaces. For weak to intermediate PNIPAM-surface interactions, the MD simulations show thermo-responsive behavior as characteristic changes of the radius of gyration and other measures of the polymer structure and polymer-water interactions, when comparing simulations below (at 280 K) and above (at 320 K) the lower critical solution temperature of PNIPAM, which is at 305 K. When the PNIPAM-surface interactions become stronger, the polymer loses its thermo-responsive behavior and is adsorbed flatly on the pore walls at both investigated temperatures. © 2013 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.molliq.2013.05.022
  • 2014 • 160 Effects of laser sintering processing time and temperature on changes in polyamide 12 powder particle size, shape and distribution
    Mielicki, C. and Gronhoff, B. and Wortberg, J.
    AIP Conference Proceedings 1593 728-731 (2014)
    In laser sintering (LS) un-molten Polyamide 12 (PA12) powder is usually re-used (recycled) in further processes. However, LS processing time at powder bed temperature leads to material property changes. As a consequence, un-molten PA12 powder that is re-used or recycled in further processes leads to process and part properties deviations. In this context, powder particle size, shape and distribution is assumed to affect surface roughness and porosity of LS parts. In order to investigate this process effect on changes in powder size, shape and distribution, PA12 powder was systematically aged in a vacuum oven at conditions close to the LS process. According to this procedure, polymeric powder was obtained with aging times up to 120 hours and analyzed by dynamic image analysis. At first, fresh powder was investigated as a reference. The effect of LS processing time and temperature, i.e. powder bed temperature of approx. 174°C was measured with respect to changes in size distribution and shape whereas particles were considered of size up to 500μm. The influence of LS processing time at powder bed temperature was found to be neither significant on changes in particle size nor distribution. With respect to particle shape, a higher deviation to the reference was observed for particle size bigger than 100 μm and longer aging times. Consequently, influences on particle shape changes on surface roughness are assumed to be more likely than influences on part porosity due to LS processing conditions. © 2014 American Institute of Physics.
    view abstractdoi: 10.1063/1.4873880
  • 2014 • 159 Rheological changes of polyamide 12 under oscillatory shear
    Mielicki, C. and Gronhoff, B. and Wortberg, J.
    AIP Conference Proceedings 1593 231-235 (2014)
    Changes in material properties as well as process deviation prevent Laser Sintering (LS) technology from manufacturing of quality assured parts in a series production. In this context, the viscosity of Polyamide 12 (PA12) is assumed to possess the most significant influence, as it determines the sintering velocity, the resistance towards melt formation and the bonding strength of sintered layers. Moreover, the viscosity is directly related to the structure of the molten polymer. In particular, it has been recently reported that LS process conditions lead to structural changes of PA12 affecting viscosity and coalescence of adjacent polymer particles, i.e. melt formation significantly. Structural change of PA12 was understood as a post condensation. Its influence on viscosity was described by a time and temperature depending rheological model whereas time dependence was considered by a novel structural change shift factor which was derived from melt volume rate data. In combination with process data that was recorded using online thermal imaging, the model is suitable to control the viscosity (processability of the material) as result of material and process properties. However, as soon as laser energy is exposed to the powder bed PA12 undergoes a phase transition from solid to molten state. Above the melting point, structural change is expected to occur faster due to a higher kinetic energy and free volume of the molten polymer. Oscillatory shear results were used to study the influence of aging time and for validation of the novel structural change shift factor and its model parameters which were calibrated based on LS processing condition. © 2014 American Institute of Physics.
    view abstractdoi: 10.1063/1.4873770
  • 2014 • 158 Various strategies for the immobilization of biocatalysts on textile carrier materials
    Opwis, K. and Straube, T. and Kiehl, K. and Gutmann, J.S.
    Chemical Engineering Transactions 38 223-228 (2014)
    Textile fabrics made of polyester (PET), polyamide (PA) or cotton represent alternative carrier materials for the immobilization of enzymes. In contrast to conventional carriers, fiber materials are considerably inexpensive. The flexible construction of fabrics enables reactor constructions of any geometry and a quick removal of the catalyst without any residues after the reaction. Moreover, their open structure guarantees an optimal substrate turn-over and the active surface is easily adjustable by the fiber diameter. We have demonstrated successfully, that fabrics with a high enzyme load, a high relative activity and good permanence against enzyme desorption can be produced with low preparative and economic expense. Here, we report various methods for the permanent fixation of enzymes on fiber forming polymers such as photochemical grafting, the use of bifunctional anchor molecules, monomeric and polymeric cross-linking agents or specific enzyme modification for direct immobilization. In addition, we compare the strategies in terms of load, catalytic activity and reusability. © 2014, AIDIC Servizi S.r.l.
    view abstractdoi: 10.3303/CET1438038
  • 2014 • 157 A miniaturized voltammetric pH sensor based on optimized redox polymers
    Pöller, S. and Schuhmann, W.
    Electrochimica Acta 140 101-107 (2014)
    A miniaturized pH sensor based on the voltammetric determination of the potential difference between a pH dependent toluidine blue O modified redox polymer and a pH independent osmium complex modified redox polymer was developed. Gold micro electrodes of various dimensions were modified with the two redox polymers by non-manual deposition procedures. Square wave voltammetry was used to determine the oxidation potentials of the polymer bound redox species allowing the precise determination of the pH value of the electrolyte solution without the need of a stable reference electrode. © 2014 Elsevier Ltd.
    view abstractdoi: 10.1016/j.electacta.2014.03.116
  • 2014 • 156 Thermodynamic phase behavior of API/polymer solid dispersions
    Prudic, A. and Ji, Y. and Sadowski, G.
    Molecular Pharmaceutics 11 2294-2304 (2014)
    To improve the bioavailability of poorly soluble active pharmaceutical ingredients (APIs), these materials are often integrated into a polymer matrix that acts as a carrier. The resulting mixture is called a solid dispersion. In this work, the phase behaviors of solid dispersions were investigated as a function of the API as well as of the type and molecular weight of the carrier polymer. Specifically, the solubility of artemisinin and indomethacin was measured in different poly(ethylene glycol)s (PEG 400, PEG 6000, and PEG 35000). The measured solubility data and the solubility of sulfonamides in poly(vinylpyrrolidone) (PVP) K10 and PEG 35000 were modeled using the perturbed-chain statistical associating fluid theory (PC-SAFT). The results show that PC-SAFT predictions are in a good accordance with the experimental data, and PC-SAFT can be used to predict the whole phase diagram of an API/polymer solid dispersion as a function of the kind of API and polymer and of the polymers molecular weight. This remarkably simplifies the screening process for suitable API/polymer combinations. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/mp400729x
  • 2014 • 155 Influence of copolymer composition on the phase behavior of solid dispersions
    Prudic, A. and Kleetz, T. and Korf, M. and Ji, Y. and Sadowski, G.
    Molecular Pharmaceutics 11 4189-4198 (2014)
    The incorporation of poorly soluble active pharmaceutical ingredients (APIs) into excipients (e.g., polymers) to formulate an amorphous solid dispersion is a promising strategy to improve the oral bioavailability of the API. The application of copolymer excipients allows access to combinations of different monomers and thus to the design of excipients to improve solid-dispersion properties. In this work, the thermodynamic phase behavior of solid dispersions was investigated as a function of the API, type of monomer, and copolymer composition. The glass-transition temperatures and API solubilities in the solid dispersions of naproxen and indomethacin in polyvinylpyrrolidone, polyvinyl acetate, and copolymers with different weight fractions of vinylpyrrolidone and vinyl actetate were investigated. It is shown that the thermodynamic phase behavior of API/copolymer solid dispersions is a function of monomer type and copolymer composition. This effect was also predicted by using the perturbed-chain statistical associating fluid theory (PC-SAFT). The glass-transition temperature of the solid dispersions was calculated with the Gordon-Taylor equation. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/mp500412d
  • 2014 • 154 Urease-induced calcification of segmented polymer hydrogels - A step towards artificial biomineralization
    Rauner, N. and Meuris, M. and Dech, S. and Godde, J. and Tiller, J.C.
    Acta Biomaterialia 10 3942-3951 (2014)
    Natural organic/inorganic composites, such as nacre, bones and teeth, are perfectly designed materials with exceptional mechanical properties. Numerous approaches have been taken to synthetically prepare such composites. The presented work describes a new way of mineralizing bulk materials on a large scale following the approach of bioinduced mineralization. To this end, a series of polymer conetworks with entrapped urease were prepared. After polymerization, the entrapped urease shows high enzymatic activity. The bioactive polymer conetworks were then treated with an aqueous mixture of urea and CaCl2. The urease-induced calcification indeed allows formation of carbonate crystals exclusively within the hydrogel even at room temperature. The influence of network composition, degree of cross-linking, immobilized urease concentration and temperature of calcification were investigated. By varying these parameters, spherical, monolithic clusters, as well as bar-like nanocrystals with different aspect ratios in spherical or dendritic arrays, are formed. The grown nanocrystals improve the stiffness of the starting material by up to 700-fold, provided that the microstructure shows a dense construction without pores and strong interaction between crystals and network. The process has the potential to generate a new class of hybrid materials that would be available on the macroscopic scale for use in lightweight design and medicine. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.actbio.2014.05.021
  • 2014 • 153 Modeling aqueous two-phase systems: II. Inorganic salts and polyether homo- and copolymers as ATPS former
    Reschke, T. and Brandenbusch, C. and Sadowski, G.
    Fluid Phase Equilibria 375 306-315 (2014)
    In this work the electrolyte perturbed chain statistical associating fluid theory (ePC-SAFT) was applied to model aqueous two-phase systems (ATPS) containing combinations of polyethylene glycol dimethyl ether (PEGDME), polypropylene glycol (PPG) and three poly(ethylene glycol-co-propylene glycol) copolymers in combination with 12 different inorganic salts for temperatures ranging from 278. K to 333. K. For the polymer modeling, a copolymer approach was applied splitting the polymer in different segment types accounting for their different molecular interactions. Using this approach allows for quantitative modeling of phase properties of aqueous homopolymer and copolymer solutions. ATPS consisting of water, salt and one out of the five polymers were successfully modeled by using only one binary interaction parameter between each polymer segment type and each ion. Applying these parameter set, the influence of (co)polymer composition, polymer molecular weight, and temperature on the phase composition and phase densities could be modeled accurately. © 2014.
    view abstractdoi: 10.1016/j.fluid.2014.04.040
  • 2014 • 152 New nanofibrous scaffold for corneal tissue engineering
    Salehi, S. and Grünert, A.K. and Bahners, T. and Gutmann, J.S. and Steuhl, K.P. and Czugala, M. and Singer, B.B. and Fuchsluger, T.A.
    Klinische Monatsblatter fur Augenheilkunde 231 626-630 (2014)
    Background: An estimated 10 million people suffer worldwide from vision loss caused by corneal damage. For the worst cases, the only available treatment is transplantation with human donor corneal tissue. However, in numerous countries there is a considerable shortage of corneal tissue of good quality, leading to various efforts to develop tissue substitutes. The present study aims to introduce a nanofibrous scaffold of poly(glycerol sebacate) PGS as a biodegradable implant, for the corneal tissue engineering. Materials and Methods: Nanofibrous scaffolds were produced from PGS and poly(ε- caprolactone) (PCL) by a modified electro-spinning process. The biocompatibility of the material was tested in vitro by colorimetric MTT assay on days 3, 5, and 7 to test the cell viability of human corneal endothelium cells (HCEC). To examine a potential immunological reaction of the scaffolds, samples were exposed to mononuclear cells derived from peripheral blood (PBMCs). After an incubation period of 3 days, supernatants were assayed for apoptotic assessment and immunogenic potentials by annexin V FITC//propidium iodide and flow-cytometric analysis. Results: We could successfully demonstrate that cultivation of HCECs on PGS/PCL scaffolds was possible. Compared to day 3, cell density determined by microplate absorbance was significantly higher after 7 days of cultivation (p 0.0001). According to the MTT data, none of the samples showed toxicity. Apoptotic assessments by FACS analysis showed that no composition stimulated apoptosis or activated PBMCs occurred. All the compositions were inert for native as well as activated T/B/NK cells and monocytes. It can be concluded that leukocytes and their activity was not affected by the scaffolds. Conclusion: A tissue-like scaffold mimicking the human stroma could be developed. The results indicate that PGS/PCL scaffolds could be considered as ideal candidates for corneal tissue engineering as they are biocompatible in contact to corneal endothelial cells and blood cells. © 2014 Georg Thieme Verlag KG Stuttgart New York.
    view abstractdoi: 10.1055/s-0034-1368533
  • 2014 • 151 Cellobiose dehydrogenase entrapped within specifically designed Os-complex modified electrodeposition polymers as potential anodes for biofuel cells
    Shao, M. and Guschin, D.A. and Kawah, Z. and Beyl, Y. and Stoica, L. and Ludwig, R. and Schuhmann, W. and Chen, X.
    Electrochimica Acta 128 318-325 (2014)
    Electron-transfer pathways between cellobiose dehydrogenase from Myriococcum thermophilum (MtCDH) and the related flavodehydrogenase domain (FAD-MtCDH) and electrodes were evaluated using specifically designed Os-complex modified electrodeposition paints (EDPs). The properties of the Os-complex modified EDPs were varied by variation of the monomer composition, the coordination sphere of the polymer-bound Os-complexes, and the length and flexibility of the spacer chain between Os complex and polymer backbone. The MtCDH-to-EDP weight ratio, the pH value, as well as the operational temperature have been optimized. © 2013 Elsevier Ltd.
    view abstractdoi: 10.1016/j.electacta.2013.11.019
  • 2014 • 150 High-concentration graphene dispersions with minimal stabilizer: a scaffold for enzyme immobilization for glucose oxidation
    Sun, Z. and Vivekananthan, J. and Guschin, D.A. and Huang, X. and Kuznetsov, V. and Ebbinghaus, P. and Sarfraz, A. and Muhler, M. and Schuhmann, W.
    Chemistry (Weinheim an der Bergstrasse, Germany) 20 5752-5761 (2014)
    Modified acrylate polymers are able to effectively exfoliate and stabilize pristine graphene nanosheets in aqueous media. Starting with pre-exfoliated graphite greatly promotes the exfoliation level. The graphene concentration is significantly increased up to 11 mg mL(-1) by vacuum evaporation of the solvent from the dispersions under ambient temperature. TEM shows that 75 % of the flakes have fewer than five layers with about 18 % of the flakes consisting of monolayers. Importantly, a successive centrifugation and redispersion strategy is developed to enable the formation of dispersions with exceptionally high graphene-to-stabilizer ratio. Characterization by high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy shows the flakes to be of high quality with very low levels of defects. These dispersions can act as a scaffold for the immobilization of enzymes applied, for example, in glucose oxidation. The electrochemical current density was significantly enhanced to be approximately six times higher than an electrode in the absence of graphene, thus showing potential applications in enzymatic biofuel cells. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/chem.201400098
  • 2014 • 149 The calibration of numerically simulated color and material change processes
    Szöke, L. and Wortberg, J.
    AIP Conference Proceedings 1593 628-631 (2014)
    As shown in the past, the first steps of product changing processes within extrusion dies can be observed through numerical simulations using transient calculations and the volume of fluid (VOF) approach. However, in the later part of the changing process, influences from the system, such as surface properties of the die channel or particle types in the polymer, govern the progress of the melt flow directly at the wall. Recently an approach allows these effects to be implemented into the numerical simulation despite the complexity of the whole flow system. In general it is common to assume a zero velocity at the channel wall in fluid dynamic calculations. In reality the exchange of materials during the extrusion process can be observed. Therefore, a finite velocity at the wall has to exist. Although this velocity is very low, it cannot be ignored for product changes as for most other calculations, because the velocity of the source material at the wall dominates the time or the amount of target material needed to complete the change. To calibrate the numerical calculation considering the effects near the channel wall a correcting function based on the experimental data is used. Therefore a wall velocity is calculated analytically and implemented as boundary condition in the numerical computation. This function is based on experimental data from color and material changes of several low density polyethylene (LDPE) types. © 2014 American Institute of Physics.
    view abstractdoi: 10.1063/1.4873858
  • 2014 • 148 Impact of the configuration of a chiral, activating carrier on the enantioselectivity of entrapped lipase from Candida rugosa in cyclohexane
    Tobis, J. and Tiller, J.C.
    Biotechnology Letters 36 1661-1667 (2014)
    Lipase from Candida rugosa was loaded into an amphiphilic polymer co-network (APCN) composed of the chiral poly[(R)-N-(1-hydroxybutan-2-yl) acrylamide] [P-(R)-HBA] and P-(S)-HBA, respectively, linked by poly(dimethylsiloxane). The nanophase-separated amphiphilic morphology affords a 38,000-fold activation of the enzyme in the esterification of 1-phenylethanol with vinyl acetate. Further, the enantioselectivity of the entrapped lipase was influenced by the configuration of the chiral, hydrophilic polymer matrix. While the APCN with the (S)-configuration of the APCN affords 5.4 faster conversion of the (R)-phenylethanol compared to the respective (S)-enantiomer, the (R)-APCN allows an only a 2.8 faster conversion of the (R)-enantiomer of the alcohol. Permeation-experiments reveal that the enantioselectivity of the reaction is at least partially caused by specific interactions between the substrates and the APCN. © 2014 Springer Science+Business Media Dordrecht.
    view abstractdoi: 10.1007/s10529-014-1519-0
  • 2014 • 147 The role of hydrophobicity of Os-complex-modified polymers for photosystem 1 based photocathodes
    Zhao, F. and Sliozberg, K. and Rögner, M. and Plumeré, N. and Schuhmann, W.
    Journal of the Electrochemical Society 161 H3035-H3041 (2014)
    The integration of photosystem 1 in redox hydrogels based on Os-complexes modified redox polymers on electrodes yields efficient photocathodes. The generation of high photocurrent relies on high loading in PS1 and fast electron transfer rates from the electrode to PS1. The interaction between the redox polymer and PS1 influences both the loading in protein and the electron transfer rates. Since PS1 exhibits extended hydrophobic regions, polymers with similar properties may favor attractive interactions. Here we investigate three approaches to confer hydrophobicity to the redox polymer. We demonstrate that the pyridine functionality enables to switch, via basic pH values, the polymer properties from hydrophilic to hydrophobic. The transition triggers a hydrogel collapse which allows for efficient entrapment of PS1. In addition the hydrophobic-hydrophilic balance was tuned by the addition of hydrophobic group in i) the polymer backbone and ii) as substituents at the Os-complex. The increased hydrophobicity of the backbone results in higher photocurrents from PS1 integrated in the corresponding hydrogel. On the other hand, further increasing hydrophobicity of the redox relay decreases the photocurrent due to either lower mobility of the Os-complexes or poor interaction with the hydrophilic site where the redox center of PS1 is located. © The Author(s) 2014. Published by ECS.
    view abstractdoi: 10.1149/2.0081413jes
  • 2013 • 146 A new class of nanoengines based on thermoresponsive polymers: Conceptual design and behavior study
    Alaghemandi, M. and Spohr, E.
    Chemical Physics Letters 581 80-84 (2013)
    A model nanoengine based on endgrafted Poly(N-isopropylacrylamide) (PNIPAM) on graphene-like sheets is proposed. The nanoengine consists of a water-filled slab and four PNIPAM chains, which are at one end grafted to one of the slab walls and on the other end to a mobile square graphene 'piston'. The basis of the reciprocating motion of the piston is the reversible coil-to-globule transition of polymer chains when changing the temperature of the aqueous environment. Molecular dynamics simulations have been used to investigate the behavior of the proposed system at the full atomistic level. At temperatures below the lower critical solution temperature (LCST) PNIPAM chains are swollen and the nanopiston is in an expanded open state. Above the LCST, the PNIPAM chains are shrunken and the piston is retracted. The studied nanopiston exhibits an amplitude of approximately 10 Å when the temperature is reduced from 310 to 300 K or increased from 300 to 310 K with a frequency of about 10 9 rotations per minute; however the efficiency is very low. © 2013 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.cplett.2013.07.017
  • 2013 • 145 A porous pH-stabilized composite material consisting of poly (D,L-lactide), calcium carbonate and gentamicin for bone substitution
    Backhaus, S. and Annen, T. and Epple, M.
    Materialwissenschaft und Werkstofftechnik 44 107-111 (2013)
    Macroporous objects of poly(D,L-lactide), PDLLA, and calcium carbonate were prepared by hot-pressing (0% porosity), gas-foaming (50% porosity), and a combination of gas-foaming and salt leaching (70% porosity). They were loaded with 15 wt% of gentamicin without loss of the mechanical properties. The release of gentamicin occurred over several weeks, making this material suitable as a mechanically stable porous and degradable bone substitution material with antibacterial properties. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/mawe.201300081
  • 2013 • 144 Electric properties of organic thin-layers deposited by photo-polymerization on a textile substrate
    Bahners, T. and Wego, A. and Gutmann, J.S.
    Progress in Organic Coatings 76 1581-1585 (2013)
    The scope of the reported experiments was to study the charging behavior of photo-polymerized poly-DAP, poly-TAE and poly-PETA thin-layers, namely the remanence or storage of artificially deposited electric charges. The thin-layers were polymerized on the fibers of a technical non-woven under variation of the main parameters of the polymerization process, namely the monomer concentration in the applied precursor and the duration of UV exposure. The charging behavior of the layers was characterized by recording the charge dissipation after defined surface charging by a corona discharge. After the artificial charging, the electric field generated by residual surface charges was measured using an electric field mill as a function of time. It was found that the poly-DAP thin-layer showed no improvement in charge decay over the untreated sample. This is attributed to water absorption due to carboxylic groups. Poly-TAE and poly-PETA showed significant increases in charge remanence with increasing polymerization. It is proposed that the observed change in the electric property is related to increased cross-linking and reduced chain mobility with increasing UV exposure. Best results were achieved with poly-TAE holding, a thin-layer holding 1/e of the initial charge after more than 10 min. © 2012 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.porgcoat.2013.07.001
  • 2013 • 143 Advanced nanoparticle generation and excitation by lasers in liquids
    Barcikowski, S. and Compagnini, G.
    Physical Chemistry Chemical Physics 15 3022-3026 (2013)
    Today, nanoparticles are widely implemented as functional elements onto surfaces, into volumes and as nano-hybrids, resulting for example in bioactive composites and biomolecule conjugates. However, only limited varieties of materials compatible for integration into advanced functional materials are available: nanoparticles synthesized using conventional gas phase processes are often agglomerated into micro powders that are hard to re-disperse into functional matrices. Chemical synthesis methods often lead to impurities of the nanoparticle colloids caused by additives and precursor reaction products. In the last decade, laser ablation and nanoparticle generation in liquids has proven to be a unique and efficient technique to generate, excite, fragment, and conjugate a large variety of nanostructures in a scalable and clean manner. This editorial briefly highlights selected recent advancements and critical aspects in the field of pulsed laser-based nanoparticle generation and manipulation, including exemplary strategies to harvest the unique properties of the laser-generated nanomaterials in the field of biomedicine and catalysis. The presented critical aspects address future assignments such as size control and scale-up. This journal is © 2013 the Owner Societies.
    view abstractdoi: 10.1039/c2cp90132c
  • 2013 • 142 Synthesis and crystal structure of a salt containing ∞ 1{Zn[trans-μ2(η3: η3-Ge9)]}2- anions: A polymer with Ge 9 zintl clusters bridged by Zn atoms
    Benda, C.B. and Schäper, R. and Schulz, S. and Fässler, T.F.
    European Journal of Inorganic Chemistry 5964-5968 (2013)
    The reaction of an ethylenediamine (en) solution of K4Ge 9 with Zn2(Mesnacnac)2 {Mesnacnac = [(2,4,6-Me3C6H2)NC(Me)]2CH} in the presence of 18-crown-6 (18-crown-6 = 1,4,7,10,13,16-hexaoxacyclooctadecane) leads to the formation of the new compound [K(18-crown-6)]2{Zn[trans- μ2(η3:η3-Ge9)]}(en). A crystallographic structure determination revealed that the salt contains ∞ 1[Zn(Ge9)]2- polyanions in which each Zn atom bridges two Ge9 clusters by coordinating to opposite triangular faces of the Ge9 deltahedra. The polymeric chain can be formally described as consisting of a trans ZnII complex with two [η3:η3-Ge9]4- ligands. 1H NMR spectroscopic investigations indicated that the protonation of the Mesnacnac- ligand by the solvent ethylenediamine plays a crucial role in the disproportionation of the ZnI starting material and thus in the formation of the polymeric ZnII complex. In contrast, the reaction of ZnPh2 instead of Zn2(Mesnacnac)2 under the same conditions leads to the known complex [PhZn(η4- Ge9)]3-. Crystals of the compound [K(18-crown-6)] 2{Zn[trans-μ2(η3:η3- Ge9)]}(en), containing strands of ∞ 1{Zn[trans-μ2(η3:η3- Ge9)]}2- units in which Zn atoms connect Ge9 clusters in an η3-fashion, were obtained by the reaction of the binary Zintl phase K4Ge9 with Zn2(Mesnacnac) 2 (Mesnacnac = [(2,4,6-Me3C6H 2)NC(Me)]2CH) in ethylenediamine (en). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/ejic.201301122
  • 2013 • 141 Salen-based coordination polymers of manganese and the rare-earth elements: Synthesis and catalytic aerobic epoxidation of olefins
    Bhunia, A. and Gotthardt, M.A. and Yadav, M. and Gamer, M.T. and Eichhöfer, A. and Kleist, W. and Roesky, P.W.
    Chemistry - A European Journal 19 1986-1995 (2013)
    Treatment of N,N'-bis(4carboxysalicylidene)ethylenediamine (H 4L), with MnCl2·(H2O)4, and Ln(NO3)3·(H2O)m (Ln=Nd, Eu, Gd, Dy, Tb), in the presence of N,N-dimethylformamide (DMF)/pyridine at elevated temperature resulted (after work up) in the formation of 1D coordination polymers {[Ln2(MnLCl)2(NO3)2(dmf) 5]·4 DMF}n (1-5). In these coordination polymers the rare earth ions are connected through carboxylate groups from Mn-salen units in a 1D chain structure. Thus, the Mn-salen complex acts as a "metalloligand" with open coordination sites. All compounds were used as catalysts in the liquid-phase epoxidation of trans-stilbene with molecular oxygen, which resulted in the formation of stilbene oxide. Since the choice of the lanthanide had virtually no influence on the performance of the catalyst, only the manganese-gadolinium was studied in detail. The influence of solvent, catalyst concentration, reaction temperature, oxidant, and oxidant flow rate on conversion, yield, and selectivity was analyzed. A conversion of up to 70 %, the formation of 61 % stilbene oxide (88 % selectivity), and a TON of 84 were observed after 24 h. A hot filtration test confirmed that the reaction is mainly catalyzed through a heterogeneous pathway, although a minor contribution of homogeneous species could not be completely excluded. The catalyst could be reused without significant loss of activity. Copyright © 2013 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/chem.201203636
  • 2013 • 140 Polymer modified jute fibre as reinforcing agent controlling the physical and mechanical characteristics of cement mortar
    Chakraborty, S. and Kundu, S.P. and Roy, A. and Adhikari, B. and Majumder, S.B.
    Construction and Building Materials 49 214-222 (2013)
    Polymer modified alkali treated jute fibre as a reinforcing agent, substantially improves the physical and mechanical properties of cement mortar with a mix design cement:sand:fibre:water::1:3:0.01:0.6. The workability of the mortar is found to increase systematically from 155 ± 5 mm (control mortar) to 167 ± 8 mm (0.2050% polymer modified mortar). The density of the mortar is increased from 2092 kg/m3 to 2136 kg/m3 with a concomitant reduction of both water absorption and apparent porosity. Optimal polymer content in emulsion (0.0513%) is found to increase the compressive strength, modulus of rupture and flexural toughness 25%, 28%, 387% respectively as compared to control mortar. Based on the X-ray diffraction and infra-red spectroscopy analyses of the mortar samples a plausible mechanism of the effect of modified jute fibre controlling the physical and mechanical properties of cement mortar has been proposed. © 2013 Elsevier Inc. All rights reserved.
    view abstractdoi: 10.1016/j.conbuildmat.2013.08.025
  • 2013 • 139 Particle beam experiments for the analysis of reactive sputtering processes in metals and polymer surfaces
    Corbella, C. and Grosse-Kreul, S. and Kreiter, O. and de los Arcos, T. and Benedikt, J. and von Keudell, A.
    Review of Scientific Instruments 84 103303 (2013)
    A beam experiment is presented to study heterogeneous reactions relevant to plasma-surface interactions in reactive sputtering applications. Atom and ion sources are focused onto the sample to expose it to quantified beams of oxygen, nitrogen, hydrogen, noble gas ions, and metal vapor. The heterogeneous surface processes are monitored in situ by means of a quartz crystal microbalance and Fourier transform infrared spectroscopy. Two examples illustrate the capabilities of the particle beam setup: oxidation and nitriding of aluminum as a model of target poisoning during reactive magnetron sputtering, and plasma pre-treatment of polymers (PET, PP). (C) 2013 AIP Publishing LLC.
    view abstractdoi: 10.1063/1.4826066
  • 2013 • 138 Understanding the reduced efficiencies of organic solar cells employing fullerene multiadducts as acceptors
    Faist, M.A. and Shoaee, S. and Tuladhar, S. and Dibb, G.F.A. and Foster, S. and Gong, W. and Kirchartz, T. and Bradley, D.D.C. and Durrant, J.R. and Nelson, J.
    Advanced Energy Materials 3 744-752 (2013)
    The use of fullerenes with two or more adducts as acceptors has been recently shown to enhance the performance of bulk-heterojunction solar cells using poly(3-hexylthiophene) (P3HT) as the donor. The enhancement is caused by a substantial increase in the open-circuit voltage due to a rise in the fullerene lowest unoccupied molecular orbital (LUMO) level when going from monoadducts to multiadducts. While the increase in the open-circuit voltage is obtained with many different polymers, most polymers other than P3HT show a substantially reduced photocurrent when blended with fullerene multiadducts like bis-PCBM (bis adduct of Phenyl-C61-butyric acid methyl ester) or the indene C 60 bis-adduct ICBA. Here we investigate the reasons for this decrease in photocurrent. We find that it can be attributed partly to a loss in charge generation efficiency that may be related to the LUMO-LUMO and HOMO-HOMO (highest occupied molecular orbital) offsets at the donor-acceptor heterojunction, and partly to reduced charge carrier collection efficiencies. We show that the P3HT exhibits efficient collection due to high hole and electron mobilities with mono- and multiadduct fullerenes. In contrast the less crystalline polymer Poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5- thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl (PCDTBT) shows inefficient charge carrier collection, assigned to low hole mobility in the polymer and low electron mobility when blended with multiadduct fullerenes. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/aenm.201200673
  • 2013 • 137 Redox active polymer brushes with phenothiazine moieties
    Golriz, A.A. and Kaule, T. and Untch, M.B. and Kolman, K. and Berger, R. and Gutmann, J.S.
    ACS Applied Materials and Interfaces 5 2485-2494 (2013)
    We have investigated two different concepts to synthesize redox active polymer brushes using surface initiated atomic transfer radical polymerization (SI-ATRP). This polymerization technique allows the synthesis of well-defined grafted polymer brushes. In the initial step the surface was functionalized with a self-assembling monolayer of the SI-ATRP starter. Then, polymer brushes carrying phenothiazine moieties were grafted from the surface via SI-ATRP. The first concept consists of polymerizing monomers with phenothiazine pendant moieties to directly incorporate the redox functionality as side group in the growing polymer brush. The second concept consists of using grafted activated ester brushes which are functionalized with phenothiazine redox moieties in a successive reaction step. The electrochemical properties of the grafted redox active brushes were examined by cyclic voltammetry. Furthermore, the surface morphology and the chemical composition of the polymer brushes were characterized using scanning force microscopy (SFM), X-ray techniques, and UV/vis spectroscopy. Apart from their redox behavior, the synthesized brushes revealed increased mechanical stability on the nanoscale. © 2013 American Chemical Society.
    view abstractdoi: 10.1021/am302869d
  • 2013 • 136 Chemical and Physical Sputtering of Polyethylene Terephthalate (PET)
    Grosse-Kreul, S. and Corbella, C. and von Keudell, A.
    Plasma Processes and Polymers 10 225--234 (2013)
    The polymer polyethylene terephthalate (PET) has been exposed to quantified beams of argon ions and oxygen atoms and molecules. The etch rate (ER) and the surface composition of PET thin films have been analyzed by real time in situ Fourier transform infrared spectroscopy (FTIR). After the onset of the exposure of PET to the ion beam, the ER decreases rapidly by one order of magnitude irrespective of the ion energy. This slowing down of the ER is caused by cross-linking of the polymer surface. The steady state etch yields are generally orders of magnitude higher than predicted by computer calculations. The addition of oxygen to the particle flux is only changing the surface composition. At low ion energies, chemical sputtering dominates causing very high sputter yields. In addition, no threshold ion energy is observed. [GRAPHICS] .
    view abstractdoi: 10.1002/ppap.201200094
  • 2013 • 135 Hierarchical self-assembly of miktoarm star polymers containing a polycationic segment: A general concept
    Hanisch, A. and Gröschel, A.H. and Förtsch, M. and Löbling, T.I. and Schacher, F.H. and Müller, A.H.E.
    Polymer (United Kingdom) 54 4528-4537 (2013)
    We recently introduced a concept for the counterion-mediated hierarchical self-assembly of an amphiphilic ABC miktoarm star terpolymer in aqueous media into micrometer-sized compartmentalized particles with a highly periodic lamellar fine structure ("woodlice"). Herein, we extend this concept to different miktoarm star polymer systems containing a polycationic segment. The presence of a poly(N-methyl-2-vinylpyridinium) (P2VPq) block and its interaction with iodide/triiodide counterions is crucial. In analogy to linear diblock copolymer systems the hydrophilic/hydrophobic balance of polybutadiene-arm-poly(N-methyl-2-vinylpyridinium iodide)-arm-polystyrene miktoarm star terpolymers determines the morphology of the primary building blocks (spherical micelles and cylindrical micelles/vesicles) and the obtained superstructures (stacked lamellar structures and multilamellar vesicles) during this hierarchical process. When an ABA' miktoarm star copolymer (polystyrene-arm-poly(N-methyl-2-vinylpyridinium iodide)-arm-polystyrene) without a dynamic core-forming block was investigated, a different mechanism into "woodlouse" structured aggregates via aggregation and deformation of intermediate vesicles was found. The individual steps of the different self-assembly processes were investigated by transmission electron microscopy and additionally supported by dynamic light scattering, differential scanning calorimetry, and small-angle X-ray scattering. © 2013 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.polymer.2013.05.071
  • 2013 • 134 Counterion-mediated hierarchical self-assembly of an ABC miktoarm star terpolymer
    Hanisch, A. and Gröschel, A.H. and Förtsch, M. and Drechsler, M. and Jinnai, H. and Ruhland, T.M. and Schacher, F.H. and Müller, A.H.E.
    ACS Nano 7 4030-4041 (2013)
    Directed self-assembly processes of polymeric systems represent a powerful approach for the generation of structural hierarchy in analogy to biological systems. Herein, we utilize triiodide as a strongly polarizable counterion to induce hierarchical self-assembly of an ABC miktoarm star terpolymer comprising a polybutadiene (PB), a poly(tert-butyl methacrylate) (PtBMA), and a poly(N-methyl-2-vinylpyridinium) (P2VPq) segment. Hereby, the miktoarm architecture in conjunction with an increasing ratio of triiodide versus iodide counterions allows for a stepwise assembly of spherical micelles as initial building blocks into cylindrical structures and superstructures thereof. Finally, micrometer-sized multicompartment particles with a periodic lamellar fine structure are observed, for which we introduce the term "woodlouse". The counterion-mediated decrease in hydrophilicity of the corona-forming P2VPq block is the underlying trigger to induce this hierarchical structure formation. All individual steps and the corresponding intermediates toward these well-defined superstructures were intensively studied by scattering and electron microscopic techniques, including transmission electron microtomography. © 2013 American Chemical Society.
    view abstractdoi: 10.1021/nn400031u
  • 2013 • 133 Relating recombination, density of states, and device performance in an effi cient polymer:fullerene organic solar cell blend
    Hawks, S.A. and Deledalle, F. and Yao, J. and Rebois, D.G. and Li, G. and Nelson, J. and Yang, Y. and Kirchartz, T. and Durrant, J.R.
    Advanced Energy Materials 3 1201-1209 (2013)
    We explore the interrelation between density of states, recombination kinetics, and device performance in effi cient poly[4,8-bis-(2-ethylhexyloxy)- benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-4-(2-ethylhexyloxy-1-one) thieno[3,4-b]thiophene-2,6-diyl]:[6,6]-phenyl-C 71-butyric acid methyl ester (PBDTTT-C:PC 71 BM) bulk-heterojunction organic solar cells. We modulate the active-layer density of states by varying the polymer:fullerene composition over a small range around the ratio that leads to the maximum solar cell effi ciency (50-67 wt% PC 71 BM). Using transient and steady-state techniques, we fi nd that nongeminate recombination limits the device effi-ciency and, moreover, that increasing the PC 71 BM content simultaneously increases the carrier lifetime and drift mobility in contrast to the behavior expected for Langevin recombination. Changes in electronic properties with fullerene content are accompanied by a signifi cant change in the magnitude or energetic separation of the density of localized states. Our comprehensive approach to understanding device performance represents signifi cant progress in understanding what limits these high-effi ciency polymer:fullerene systems.© 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/aenm.201300194
  • 2013 • 132 Efficient spatial and temporal modelling of material temperatures within self-reinforced polypropylene sheets during ir radiation
    Hess, S. and Ries, A. and Kersting, P. and Heim, H.-P.
    Procedia CIRP 9 49-54 (2013)
    Polymer composites of self-reinforced fibres and a matrix composed of the same plastic material display an outstanding mechanical performance and an excellent recyclability. Hence, these materials are suitable for many practical applications. One disadvantage, however, is the narrow processing window that is caused by a strong pressure and temperature sensitivity of the self-reinforced fibres. In this paper, an approach to efficiently model the spatial and temporal temperature evolution is presented. Advanced empirical modelling techniques from the design and analysis of computer experiments are fitted to experimental data. It is shown that only a small set of experiments has to be performed in order to predict the temperatures with the desired accuracy. The required enhancements with respect to the design of experiments and the empirical models are presented.
    view abstractdoi: 10.1016/j.procir.2013.06.167
  • 2013 • 131 Shape-memory natural rubber: An exceptional material for strain and energy storage
    Heuwers, B. and Beckel, A. and Krieger, A. and Katzenberg, F. and Tiller, J.C.
    Macromolecular Chemistry and Physics 214 912-923 (2013)
    Shape-memory polymers (SMPs) are smart, responsive materials with numerous potential applications. Based on previously introduced shape-memory natural rubber (SMNR), which shows exceptional properties such as strain storage of 1000%, cold storage, cold programmability, and mechanical and thermal triggers tunable both during and after programming, different SMNRs regarding their shape-memory parameters are investigated. Furthermore, their energy-storage capability and their mechanical properties are explored. SMNRs show fixity ratios of up to 94% and excellent recovery ratios of up to 100% whereas strains even above 1000% can be stored. Energies of up to 4.88 J g-1 can be stored with efficiencies of up to 53.30%. Further, the Young's modulus of SMNR can be switched by two orders of magnitude upon triggering or programming. The energy-storage capability and shape-memory parameters of shape-memory natural rubber (SMNR) are investigated. SMNRs are able to store large strains (up to 1000%) and energies (up to 4.88 J g-1) with recovery ratios of up to 100%. Furthermore, the Young's modulus of SMNR can be switched by two orders of magnitude upon triggering or programming. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/macp.201200649
  • 2013 • 130 Stress-induced stabilization of crystals in shape memory natural rubber
    Heuwers, B. and Quitmann, D. and Hoeher, R. and Reinders, F.M. and Tiemeyer, S. and Sternemann, C. and Tolan, M. and Katzenberg, F. and Tiller, J.C.
    Macromolecular Rapid Communications 34 180-184 (2013)
    In contrast to all known shape memory polymers, the melting temperature of crystals in shape memory natural rubber (SMNR) can be greatly manipulated by the application of external mechanical stress. As shown previously, stress perpendicular to the prior programming direction decreases the melting temperature by up to 40 K. In this study, we investigated the influence of mechanical stress parallel to prior stretching direction during programming on the stability of the elongation-stabilizing crystals. It was found that parallel stress stabilizes the crystals, which is indicated by linear increase of the trigger temperature by up to 17 K. The crystal melting temperature can be increased up to 126.5 °C under constrained conditions as shown by X-ray diffraction measurements. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/marc.201200594
  • 2013 • 129 Long-term active antimicrobial coatings for surgical sutures based on silver nanoparticles and hyperbranched polylysine
    Ho, C.H. and Odermatt, E.K. and Berndt, I. and Tiller, J.C.
    Journal of Biomaterials Science, Polymer Edition 24 1589-1600 (2013)
    The goal of this study was to develop a long-term active antimicrobial coating for surgical sutures. To this end, two water-insoluble polymeric nanocontainers based on hyperbranched polylysine (HPL), hydrophobically modified by either using glycidyl hexadecyl ether, or a mixture of stearoyl/palmitoyl chloride, were synthesized. Highly stabilized silver nanoparticles (AgNPs, 2-5 nm in size) were generated by dissolving silver nitrate in the modified HPL solutions in toluene followed by reduction with L-ascorbic acid. Poly(glycolic acid)-based surgical sutures were dip-coated with the two different polymeric silver nanocomposites. The coated sutures showed high efficacies of more than 99.5% reduction of adhesion of living Staphylococcus aureus cells onto the surface compared to the uncoated specimen. Silver release experiments were performed on the HPL-AgNP modified sutures by washing them in phosphate buffered saline for a period of 30 days. These coatings showed a constant release of silver ions over more than 30 days. After this period of washing, the sutures retained their high efficacies against bacterial adhesion. Cytotoxicity tests using L929 mouse fibroblast cells showed that the materials are basically non-cytotoxic. © 2013 Taylor and Francis Group, LLC.
    view abstractdoi: 10.1080/09205063.2013.782803
  • 2013 • 128 Tunable multiple-shape memory polyethylene blends
    Hoeher, R. and Raidt, T. and Krumm, C. and Meuris, M. and Katzenberg, F. and Tiller, J.C.
    Macromolecular Chemistry and Physics 214 2725-2732 (2013)
    Shape memory polymers (SMPs) are an important class of smart materials. Usually, these polymers can be switched between two shapes. Recently, the possibility of switching more than two shapes was introduced for SMPs with relatively low strain storage capability. In this work, a lightly cross-linked polyethylene blend comprising 80 wt% EOC, 15 wt% LDPE, and 5 wt% HDPE is prepared in order to obtain a tunable multiple-shape memory polymer with high strain storage capacity. It is found that depending on the programming procedure, this SMP obtains a dual-, triple-, or quadruple-shape memory effect, with well-defined intermediate temporary shapes (retraction < 0.5% K -1) over a significantly broad temperature range (up to 30 K), large storable strains (up to 1700%), and nearly full recovery of all shapes (&gt;98.9%). A lightly cross-linked blend of different polyethylenes (EOC, LDPE, and HDPE) is prepared to gain a network exhibiting a tunable multiple-shape memory capability. The achieved material shows depending on the programming procedure a dual-, triple-, or quadruple-shape memory, with well-defined intermediate temporary shapes (retraction less then 0.5% K-1) over a significantly broad temperature range (up to 30 K), stored strains of up to 1700%, and excellent-shape memory properties. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/macp.201300413
  • 2013 • 127 Recoverable strain storage capacity of shape memory polyethylene
    Hoeher, R. and Raidt, T. and Rose, M. and Katzenberg, F. and Tiller, J.C.
    Journal of Polymer Science, Part B: Polymer Physics 51 1033-1040 (2013)
    Shape memory polymers (SMPs) are an important class of smart materials. So far the focus of such polymers was to find suited triggers for various application fields. Thus, the potential of most of these macromolecular networks regarding their maximally storable strain capability was not explored. In this study, the polyethylenes HDPE, LDPE, and ethylene-1-octene (EOC) were systematically investigated with respect to their strain storage potential. To achieve maximum strains, the polymers were chemically cross-linked in such a way that they are at the borderline between thermoplastics and elastomers. All investigated polymers showed higher strain storage than literature reported systems and exhibited excellent shape memory parameters. The highest stored strain was found for networks of EOC with fully recoverable 1400%. Interestingly, this value could not be enlarged by using EOCs with higher molecular weight, which is probably due to increasing content of entanglements as confirmed by Mooney-Rivlin. Copyright © 2013 Wiley Periodicals, Inc.
    view abstractdoi: 10.1002/polb.23301
  • 2013 • 126 Improved group contribution parameter set for the application of solubility parameters to melt extrusion
    Just, S. and Sievert, F. and Thommes, M. and Breitkreutz, J.
    European Journal of Pharmaceutics and Biopharmaceutics 85 1191-1199 (2013)
    Hot-melt extrusion is gaining importance for the production of amorphous solid solutions; in parallel, predictive tools for estimating drug solubility in polymers are increasingly demanded. The Hansen solubility parameter (SP) approach is well acknowledged for its predictive power of the miscibility of liquids as well as the solubility of some amorphous solids in liquid solvents. By solely using the molecular structure, group contribution (GC) methods allow the calculation of Hansen SPs. The GC parameter sets available were derived from liquids and polymers which conflicts with the object of prediction, the solubility of solid drugs. The present study takes a step from the liquid based SPs toward their application to solid solutes. On the basis of published experimental Hansen SPs of solid drugs and excipients only, a new GC parameter set was developed. In comparison with established parameter sets by van Krevelen/Hoftyzer, Beerbower/Hansen, Breitkreutz and Stefanis/Panayiotou, the new GC parameter set provides the highest overall predictive power for solubility experiments (correlation coefficient r = -0.87 to -0.91) as well as for literature data on melt extrudates and casted films (r = -0.78 to -0.96). © 2013 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.ejpb.2013.04.006
  • 2013 • 125 Inverse determination of modeling parameters to consider inhomogeneities of semicrystalline thermoplastics in structure simulations
    Kaiser, J.-M. and Stommel, M.
    Archive of Applied Mechanics 83 889-897 (2013)
    Two semicrystalline thermoplastics, an isotactic polypropylene (iPP, LynedllBasell Moplen HP501L) and a polyethylene-high-density (PE-HD, LynedllBasell Hostalen GC7260), were selected to approve a new approach. The developed approach allows the inverse determination of the amorphous and crystalline mechanical as well as the crystalline geometric constituents' properties. Commonly, these properties are unknown in structure simulations, and hence, the application of micromechanical models to the inhomogeneous microstructure of semicrystalline thermoplastics is restricted. Rather, a homogenous microstructure is assumed, and only one Young's modulus and Poisson's ratio are used in calculations. Thus, the quality and reliability of simulations are limited. In the current study, a new approach was exemplarily conducted for the inverse determination of the required properties by combining a Mori-Tanaka mean field approach with a genetic optimization algorithm. Conclusive results were achieved for both polymers. According to the results, the attained geometric parameters for the crystalline constituents resemble the aspect ratio of the spherulite diameter and the long period of the real crystalline microstructure, and the mechanical properties of the amorphous and crystalline constituents are located within reasonable bounds. © 2013 Springer-Verlag Berlin Heidelberg.
    view abstractdoi: 10.1007/s00419-012-0724-3
  • 2013 • 124 Controlling adsorption of semiflexible polymers on planar and curved substrates
    Kampmann, T.A. and Boltz, H.-H. and Kierfeld, J.
    Journal of Chemical Physics 139 (2013)
    We study the adsorption of semiflexible polymers such as polyelectrolytes or DNA on planar and curved substrates, e.g., spheres or washboard substrates via short-range potentials using extensive Monte Carlo simulations, scaling arguments, and analytical transfer matrix techniques. We show that the adsorption threshold of stiff or semiflexible polymers on a planar substrate can be controlled by polymer stiffness: adsorption requires the highest potential strength if the persistence length of the polymer matches the range of the adsorption potential. On curved substrates, i.e., an adsorbing sphere or an adsorbing washboard surface, the adsorption can be additionally controlled by the curvature of the surface structure. The additional bending energy in the adsorbed state leads to an increase of the critical adsorption strength, which depends on the curvature radii of the substrate structure. For an adsorbing sphere, this gives rise to an optimal polymer stiffness for adsorption, i.e., a local minimum in the critical potential strength for adsorption, which can be controlled by curvature. For two- and three-dimensional washboard substrates, we identify the range of persistence lengths and the mechanisms for an effective control of the adsorption threshold by the substrate curvature. © 2013 AIP Publishing LLC.
    view abstractdoi: 10.1063/1.4813021
  • 2013 • 123 Nanoscale thermomechanics of wear-resilient polymeric bilayer systems
    Kaule, T. and Zhang, Y. and Emmerling, S. and Pihan, S. and Foerch, R. and Gutmann, J. and Butt, H.-J. and Berger, R. and Duerig, U. and Knoll, A.W.
    ACS Nano 7 748-759 (2013)
    We explore the effect of an ultrathin elastic coating to optimize the mechanical stability of an underlying polymer film for nanoscale applications. The coating consists of a several nanometer thin plasma-polymerized norbornene layer. Scanning probes are used to characterize the system in terms of shear-force-induced wear and thermally assisted indentation. The layer transforms a weakly performing polystyrene film into a highly wear-resistive system, ideal for high-density and low-power data storage applications. The result can be understood from the indentation characteristics with a hot and sharp indenter tip. The latter gives rise to a deformation mode in the fully plastic regime, enabling a simple interpretation of the results. The softening transition and the yield stress of the system on a microsecond time scale and a nanometer size scale were obtained. We show that the plastic deformation is governed by yielding in the polystyrene sublayer, which renders the overall system soft for plastic deformation. The ultrathin protection layer contributes as an elastic skin, which shields part of the temperature and pressure and enables the high wear resistance against lateral forces. Moreover, the method of probing polymers at microsecond and nanometer size scales opens up new opportunities for studying polymer physics in a largely unexplored regime. Thus, we find softening temperatures of more than 100 °C above the polystyrene glass transition, which implies that for the short interaction time scales the glassy state of the polymer is preserved up to this temperature. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/nn305047m
  • 2013 • 122 A critical assessment of experimental methods for determining the dynamic mechanical characteristics of shape memory polymers
    Kazakevičiute-Makovska, R. and Mogharebi, S. and Steeb, H. and Eggeler, G. and Neuking, K.
    Advanced Engineering Materials 15 732-739 (2013)
    Experimental study of temperature- and frequency-dependent properties of the commercially available shape memory polymer Tecoflex™ EG 72D (TFX) (Lubrizol, USA) using dynamic mechanical analysis (DMA) technique is presented. Temperature scan DMA tests have been carried out in three distinct deformation modes, uniaxial tension, three-point bending, and simple torsion, using two different testing rigs at different test parameters (frequency, strain amplitude, and heating rate) in temperatures ranging from below to above the glass transition temperature. The influence of different test parameters and some discrepancies in the temperature-dependent storage and loss moduli (and hence the loss factor) measured by DMA in different deformation modes are discussed. Shape memory polymer Tecoflex™ is experimentally investigated by running DMA tests in three distinct deformation modes, uniaxial tension, three-point bending, and simple torsion, using two test rigs, Eplexor 500N of Gabo Qualimeter® and Modular Compact Rheometer MCR-301 of Anton Paar. It is observed that the temperature-dependent storage and loss moduli measured in different deformation modes show certain discrepancies that cannot be easily reconciled. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/adem.201200341
  • 2013 • 121 Flexible mesoporous photonic resins with tunable chiral nematic structures
    Khan, M.K. and Giese, M. and Yu, M. and Kelly, J.A. and Hamad, W.Y. and Maclachlan, M.J.
    Angewandte Chemie - International Edition 52 8921-8924 (2013)
    Colors of nature: Mimicking of the structural colors of nature was achieved by the preparation of easily accessible chiral nematic polymer composites based on phenol-formaldehyde resins templated by cellulose nanocrystals. Removal of the template led to mesoporous polymer films with unique optical and physical properties. The potential application of these materials in optical sensors was also demonstrated. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201303829
  • 2013 • 120 Correlation of electronic and magnetic properties of thin polymer layers with cobalt nanoparticles
    Kharchenko, A. and Lukashevich, M. and Popok, V. and Khaibullin, R. and Valeev, V. and Bazarov, V. and Petracic, O. and Wieck, A. and Odzhaev, V.
    Particle and Particle Systems Characterization 30 180-184 (2013)
    Nanoparticles (NPs) of cobalt are synthesized in shallow layers of polyimide using 40 keV implantation of Co+ ions with a few different fluences at various ion current densities. Nucleation of individual NPs at low fluencies and their percolation at high fluencies are crucial processes governing the electrical and magnetic properties of the metal/polymer nanocomposites that can be controlled by the implantation regimes. In particular, one can tune the magnetoresistance between negative and positive through appropriate choice of ion fluence and current density. The found non-monotonous dependence of the magnetoresistance on the applied magnetic field allows suggestion of spin-dependent domain wall scattering affecting the electron transport. The samples implanted with low fluencies demonstrate superparamagnetic behavior down to very low blocking temperatures. For high fluence (1.25 × 1017 cm-2) the transition to ferromagnetic ordering is observed that is related to the increased magnetic interaction of NPs. Nanoparticles of cobalt are synthesized in shallow layers of polyimide using low-energy implantation of cobalt ions. Nucleation of individual particles and their percolation are crucial processes governing the electrical and magnetic properties of the metal/polymer nanocomposites. By tuning the implantation regimes magnetoresistance and transitions between the superparamagnetic and ferromagnenic behavior can be controlled. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/ppsc.201200042
  • 2013 • 119 On the differences between dark and light ideality factor in polymer:Fullerene solar cells
    Kirchartz, T. and Deledalle, F. and Tuladhar, P.S. and Durrant, J.R. and Nelson, J.
    Journal of Physical Chemistry Letters 4 2371-2376 (2013)
    Ideality factors are derived from either the slope of the dark current/voltage curve or the light intensity dependence of the open-circuit voltage in solar cells and are often a valuable method to characterize the type of recombination. In the case of polymer:fullerene solar cells, the ideality factors derived by the two methods usually differ substantially. Here we investigate the reasons for the discrepancies by determining both ideality factors differentially as a function of voltage and by comparing them with simulations. We find that both the dark and light ideality factors are sensitive to bulk recombination mechanisms at the internal donor:acceptor interface, as is often assumed in the literature. While the interpretation of the dark ideality factor is difficult due to resistive effects, determining the light ideality factor differentially indicates that the open-circuit voltage of many polymer:fullerene solar cells is limited by surface recombination, which leads to light ideality factors decreasing below one at high voltage. © 2013 American Chemical Society.
    view abstractdoi: 10.1021/jz4012146
  • 2013 • 118 Amphiphilic polymer conetworks based on end group cross-linked poly(2-oxazoline) homo- and triblock copolymers
    Krumm, C. and Konieczny, S. and Dropalla, G.J. and Milbradt, M. and Tiller, J.C.
    Macromolecules 46 3234-3245 (2013)
    Novel amphiphilic polymer conetworks (APCNs) were prepared via end group cross-linking. To this end, poly(2-methyloxazoline) (PMOx), poly(2- butyloxazoline) (PBuOx), and the triblock copolymers PMOx-b-PBuOx-b-PMOx were synthesized by cationic ring-opening polymerization in varying block lengths and telechelically modified with N,N-bis(2-aminoethyl)ethylendiamine (TREN). First the cross-linking with 1,4-dibromo-2-butene (DBB) was established for the homopolymers. The swelling of those matches the theoretical value for full cross-linking, indicating that in this way "near perfect" networks could be obtained. Mixtures of the homopolymers and the triblock copolymers were cross-linked with DBB to give APCNs with similar polymer segments but different network topology. AFM showed that all formed APCNs are nanophase separated with slight structural differences in the nanostructures when comparing conetworks with similar composition but different cross-linking strategies. The more drastic difference between APCNs of different topologies was found in their swelling characteristics, which clearly proves the influence of conetwork structure on their properties. © 2013 American Chemical Society.
    view abstractdoi: 10.1021/ma4004665
  • 2013 • 117 Time-monitoring sensor based on oxygen diffusion in an indicator/polymer matrix
    Marek, P. and Velasco-Veléz, J.J. and Haas, T. and Doll, T. and Sadowski, G.
    Sensors and Actuators, B: Chemical 178 254-262 (2013)
    A time-monitoring sensor based on the oxidation of leuco methylene blue (LMB) to methylene blue (MB) was developed. The sensor changes its color from yellow to green in the presence of oxygen and was integrated into a poly(vinyl alcohol) matrix. The diffusion of the oxygen in the polymer matrix as well as the oxygen uptake due to the oxidation reaction determines the time monitoring of the sensor. A physical model has been developed that accounts for both the diffusion as well as the oxidation reaction. For this purpose, the reaction kinetics was determined experimentally. Moreover, the diffusion coefficient of oxygen was determined and concentration profiles in the polymer matrix modeled. Based on these modeling, the time sensor could be calibrated very precisely. This widely applicable, low-cost visual sensor is compatible with current technologies for the processing of plastics and can be integrated into different types of packaging, e.g. for application in freshness monitoring of consumer goods. © 2012 Elsevier B.V.
    view abstractdoi: 10.1016/j.snb.2012.12.028
  • 2013 • 116 Photocurrent Enhancement from Diketopyrrolopyrrole Polymer Solar Cells through Alkyl-Chain Branching Point Manipulation
    Meager, I. and Ashraf, R. S. and Mollinger, S. and Schroeder, B. C. and Bronstein, H. and Beatrup, D. and Vezie, M. S. and Kirchartz, T. and Salleo, A. and Nelson, J. and McCulloch, I.
    Journal of the American Chemical Society 135 11537--11540 (2013)
    Systematically moving the alkyl-chain branching position away from the polymer backbone afforded two new thieno[3,2-b]thiophene diketopyrrolopyrrole (DPPTT-T) polymers. When used as donor materials in polyrner:fullerene solar cells, efficiencies exceeding 7% were achieved without the use of processing additives. The effect of the position of the alkyl-chain branching point on the thin-film morphology was investigated using X-ray scattering techniques and the effects on the photovoltaic and charge-transport properties were also studied. For both solar cell and transistor devices, moving the branching point further from the backbone was beneficial. This is the first time that this effect has been shown to improve solar cell performance. Strong evidence is presented for changes in microstructure across the series, which is most likely the cause for the photocurrent enhancement.
    view abstractdoi: 10.1021/ja406934j
  • 2013 • 115 On the cyclic material stability of shape memory polymer
    Mogharebi, S. and Kazakeviciute-Makovska, R. and Steeb, H. and Eggeler, G. and Neuking, K.
    Materialwissenschaft und Werkstofftechnik 44 521-526 (2013)
    This paper presents the experimental study of a Thermoplastic Polyurethane (TPU) based Shape Memory Polymer (SMP) produced from granulates of commercially available EstaneTM ETE75DT3 NAT022 (Oevel Westerlo, Belgium). This polymer is characterized by Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Thermal Analysis (DMTA). The experimental procedure was designed to study the functional properties (shape fixity and shape recovery) of this shape memory polymer in multiple programming/shape-recovery cycles at three different programming temperatures. The results are displayed in the temperature-stress- strain space with focus on parameters which characterize the functional fatigue and material stability of the tested polymer during consecutive cycles. These results give a better understanding of this material class that has a potential for actuator applications in engineering. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/mawe.201300023
  • 2013 • 114 Toluene sorption in poly(styrene) and poly(vinyl acetate) near the glass transition
    Mueller, F. and Naeem, S. and Sadowski, G.
    Industrial and Engineering Chemistry Research 52 8917-8927 (2013)
    The sorption of vaporized toluene into poly(styrene) (PS) at 30 C and into poly(vinyl acetate) (PVAc) at 25 C were investigated. A Maxwell-Stefan (MS) diffusion model combined with a PC-SAFT equation of state and a mechanical spring-dashpot model was used to describe the experimental sorption profiles. The mechanical parameters of the glassy polymers, such as the Young's modulus of a neat glassy polymer and the reference viscosity at the glass transition, were determined via independent tensile creep measurements. The volatile organic compound (VOC)-concentration dependence of the viscosity was predicted using the William, Landel, and Ferry (WLF) and the Kelley-Bueche (KB) equations. The mechanical model successfully predicted the glass-transition temperature of the polymer/toluene system and the viscosity near and above the glass transition. The sorption isotherms for the pressure steps in the region of the glass transition were modeled by adjusting the MS diffusion coefficients and exhibited good agreement, both qualitative and quantitative, with the diffusion coefficients predicted by the free-volume theory. Thus, the developed diffusion model can be utilized to calculate the sorption profiles of VOCs in glassy polymers above, below, and, especially, near the glass transition. © 2013 American Chemical Society.
    view abstractdoi: 10.1021/ie302322t
  • 2013 • 113 Hofmeister effect of sodium halides on the switching energetics of thermoresponsive polymer brushes
    Naini, C.A. and Thomas, M. and Franzka, S. and Frost, S. and Ulbricht, M. and Hartmann, N.
    Macromolecular Rapid Communications 34 417-422 (2013)
    A laser temperature-jump technique is used to probe the impact of sodium halides on the temperature-dependent switching kinetics and thermodynamics of poly(N-isopropylacrylamide) brushes. An analysis on the basis of a two-state model reveals van't Hoff enthalpy and entropy changes. Sodium halides increase the endothermicity and the entropic gain of the switching process below and above Tc following the Hofmeister series: NaCl &gt; NaBr &gt; NaI. In contrast, enthalpic and entropic changes at Tc remain virtually unaffected. This provides an unprecedented insight into the underlying switching energetics of this classic stimuli-responsive polymer. Because of its model character, these results represent an essential reference on the way to unpuzzle the molecular driving forces of the Hofmeister effect. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/marc.201200681
  • 2013 • 112 Coupling osmium complexes to epoxy-functionalised polymers to provide mediated enzyme electrodes for glucose oxidation
    Ó Conghaile, P. and Pöller, S. and MacAodha, D. and Schuhmann, W. and Leech, D.
    Biosensors and Bioelectronics 43 30-37 (2013)
    Newly synthesised osmium complex-modified redox polymers were tested for potential application as mediators in glucose oxidising enzyme electrodes for application to biosensors or biofuel cells. Coupling of osmium complexes containing amine functional groups to epoxy-functionalised polymers of variable composition provides a range of redox polymers with variation possible in redox potential and physicochemical properties. Properties of the redox polymers as mediators for glucose oxidation were investigated by co-immobilisation onto graphite with glucose oxidase or FAD-dependent glucose dehydrogenase using a range of crosslinkers and in the presence and absence of multiwalled carbon nanotubes. Electrodes prepared by immobilising [P20-Os(2,2'-bipyridine)2(4-aminomethylpyridine)Cl].PF6, carbon nanotubes and glucose oxidase exhibit glucose oxidation current densities as high as 560μAcm-2 for PBS containing 100mM glucose at 0.45V vs. Ag/AgCl. Films prepared by crosslinking [P20-Os(4,4'-dimethoxy-2,2'-bipyridine)2(4-aminomethylpyridin e)Cl].PF6, an FAD-dependent glucose dehydrogenase, and carbon nanotubes achieve current densities of 215μAcm-2 in 5mM glucose at 0.2V vs. Ag/AgCl, showing some promise for application to glucose oxidising biosensors or biofuel cells. © 2012 Elsevier B.V.
    view abstractdoi: 10.1016/j.bios.2012.11.036
  • 2013 • 111 PC-SAFT based group contribution method for binary interaction parameters of polymer/solvent systems
    Peters, F.T. and Laube, F.S. and Sadowski, G.
    Fluid Phase Equilibria 358 137-150 (2013)
    Based on the PC-SAFT equation of state, a group-contribution method is developed for the determination of binary interaction parameters (kij) between polymers and solvents (GCM-kij). Applying simple geometric combination rules, the kij values can be calculated from binary interaction parameters between polymer groups and solvent groups (kps). 80 different kps values allow the calculation of a kij for polymer/solvent systems with polymers consisting of CH3, 〉CH2, 〉CH2,HDPE, 〉(CH), 〉C〈, 〉CHAr, 〉CAr and (CO)O groups and solvents containing CH3, 〉CH2, 〉(CH), 〉CH2,Cyclo, 〉(CH)Cyclo, CH2,alkene, (CH)alkene, 〉CHAr, 〉CAr, O, 〉CO and (CO)O groups. Using earlier-published group-contributions for polymer parameters (Peters et al. [2,3]) in combination with the proposed GCM-kij for polymer/solvent systems allows for predicting liquid-liquid phase equilibria, vapor-liquid phase equilibria and excess enthalpies of binary polymer/solvent and copolymer/solvent as well as ternary polymer/solvent 1/solvent 2 systems in good agreement with experimental data. © 2013 Elsevier B.V.
    view abstractdoi: 10.1016/j.fluid.2013.05.033
  • 2013 • 110 Extension of the PC-SAFT based group contribution method for polymers to aromatic, oxygen- and silicon-based polymers
    Peters, F.T. and Herhut, M. and Sadowski, G.
    Fluid Phase Equilibria 339 89-104 (2013)
    A PC-SAFT group contribution method (GCM) for polymers developed earlier [10] is extended to aromatic, oxygen- and silicon-based (co-)polymers. Polymer parameters are determined using group contributions and applying simple arithmetic and geometric combination rules. Group contributions for six new groups are identified and parameterized: &gt;CHAr, &gt;CAr, O, &gt;CO, OH and &gt;Si< . The parameterization method is applied to liquid density and binary liquid-liquid equilibria and vapor-liquid equilibria as well as to excess enthalpies of polymers containing aromatic, oxygen- and silicon-containing monomer units in an extended spectrum of nonpolar, polar and associating solvents. Modeling results using both, GCM and fitted polymer parameters, show equally-good agreement with experimental data. © 2012 Elsevier B.V.
    view abstractdoi: 10.1016/j.fluid.2012.11.031
  • 2013 • 109 Stabilizing redox polymer films by electrochemically induced crosslinking
    Pöller, S. and Koster, D. and Schuhmann, W.
    Electrochemistry Communications 34 327-330 (2013)
    Electrochemically induced crosslinking is suggested to stabilize electrodeposition polymer/enzyme films selectively on an electrode surface. 4 different protected diamine or dithiol based bi-functional crosslinkers have been synthesized, which can be activated by a pH-shift invoked by electrochemical water oxidation or proton reduction. Deprotection occurs either simultaneously or sequentially to the deposition of specifically designed redox electrodeposition polymers. The stability of the resulting polymer films was substantially enhanced as evaluated using continuous potentiodynamic cycling alternated by difference pulse voltammetry. Electrochemically induced crosslinking is compatible with biological recognition elements using Trametes hirsuta laccase or glucose oxidase entrapped within specifically adapted Os-complex modified or phenothiazine-modified redox polymers. © 2013 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.elecom.2013.07.033
  • 2013 • 108 Low potential biofuel cell anodes based on redox polymers with covalently bound phenothiazine derivatives for wiring flavin adenine dinucleotide-dependent enzymes
    Pöller, S. and Shao, M. and Sygmund, C. and Ludwig, R. and Schuhmann, W.
    Electrochimica Acta 110 152-158 (2013)
    The design of biofuel cell anodes with substantially decreased potential is a prerequisite for the development of biofuel cells with large open-circuit voltage and power density. Redox polymers with covalently attached phenothiazine derivatives such of thionine acetate, toluidine blue, azure B simultaneously providing epoxide functions for covalent binding to suitably modified electrode surfaces and crosslinking were synthesized and evaluated for their ability to transfer electrons from the FAD cofactor of the flavodehydrogenase domain of cellobiose dehydrogenase from Myriococcum thermophilum (FAD-MtCDH), the flavodehydrogenase domain of cellobiose dehydrogenase from Corynascus thermophilus (FAD-CtCDH), or glucose oxidase from Aspergillus niger (GOx). Polymer/enzyme films were covalently bound via polymer bound epoxy groups to terminal amino functions introduced to graphite electrode surfaces by electrochemically induced grafting of diaminoheptane or Boc-protected ethylene diamine (EDA). The electrodes were optimized for biocatalytic glucose oxidation with respect to the hydrophilicity of the polymer backbone, the nature of the phenothiazine derivative, the pH value, as well as the relative amount of enzyme, polymer and crosslinker. Biofuel cells based on toluidine blue-modified redox polymers with integrated FAD-MtCDH, FAD-CtCDH, or GOx in combination with a bilirubin oxidase based biocathode exhibited open-circuit voltages of more than 0.7 V and maximum power densities in the range of 4 to 6 μW cm -2 at a pH value of 7.8. © 2013 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.electacta.2013.02.083
  • 2013 • 107 Solvent-sensitive reversible stress-response of shape memory natural rubber
    Quitmann, D. and Gushterov, N. and Sadowski, G. and Katzenberg, F. and Tiller, J.C.
    ACS Applied Materials and Interfaces 5 3504-3507 (2013)
    We found that constrained shape memory natural rubber (SMNR) generates mechanical stress when exposed to solvent vapor. When the solvent vapor is removed, the material reprograms itself. This process is reversible and the stress answer is proportional to the solvent vapor concentration. Further, the stress answer is specific to the solvent. © 2013 American Chemical Society.
    view abstractdoi: 10.1021/am400660f
  • 2013 • 106 Structural mimicking of inorganic catalyst supports with polydivinylbenzene to improve performance in the selective aerobic oxidation of ethanol and glycerol in water
    Richter, F.H. and Meng, Y. and Klasen, T. and Sahraoui, L. and Schüth, F.
    Journal of Catalysis 308 341-351 (2013)
    Many forms of polymers have been prepared and studied as polymeric catalyst support for metal nanoparticles and solid acid catalysts. The nanocasted mesoporous polydivinylbenzene (PDVB)-supported platinum catalysts presented here are distinguished by their customized mesoporosity and bulk morphology that are comparable to typical carbon-and alumina-supported powdered catalysts. Platinum nanoparticles are deposited on PDVB at loadings between 1 wt% and 9 wt% and a mean size between 2.7 nm and 6.2 nm, dependent on the synthesis method. Bifunctional catalysts containing platinum and acidic functionality are prepared by gas-phase sulfonation of the Pt/PDVB catalysts. The PDVB-supported catalysts are active for the oxidation of ethanol with molecular oxygen in water with up to 94% yield of acetic acid. In the analogous oxidation of glycerol, up to 60% yield of glyceric acid is reached with the bifunctional catalyst, and the polymer-supported catalysts feature lower formation of unidentified side products than Pt/C and Pt/Al2O3. Altogether, we find the polymers to be more active than the alumina and more selective than the carbon supports and thus overall have optimized performance. © 2013 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.jcat.2013.08.014
  • 2013 • 105 Lignocellulosic jute fiber as a bioadsorbent for the removal of azo dye from its aqueous solution: Batch and column studies
    Roy, A. and Chakraborty, S. and Kundu, S.P. and Adhikari, B. and Majumder, S.B.
    Journal of Applied Polymer Science 129 15-27 (2013)
    The feasibility of the use of jute fiber for the adsorption of azo dye from an aqueous solution was evaluated with batch and fixed-bed column studies. The batch studies illustrated that dye uptake was highly dependent on different process variables, namely, the pH, initial dye concentration of the solution, adsorbent dosage, contact time, ionic strength, and temperature. The exothermic and spontaneous nature of adsorption was revealed from thermodynamic study. The equilibrium adsorption data were highly consistent with the Langmuir isotherm and yielded an R2 value of 0.999. Kinetic studies divulged that the adsorption followed a pseudo-second-order model with regard to the intraparticle diffusion. In the column studies, the total amount of adsorbed dye and the adsorption capacity decreased with increasing flow rate and increased with increasing bed height and initial dye concentration. Also, the breakthrough time and exhaustion time increased with increasing bed depth but decreased with increasing flow rate and influent dye concentration. The column performances were predicted by the application of the bed-depth service time model and Thomas model to the experimental data. The virgin and dye-adsorbed jute fiber was characterized by Fourier transform infrared spectroscopy and scanning electron microscopy analyses. The investigation suggested that jute fiber could be applied as a promising low-cost adsorbent for dye removal. Copyright © 2012 Wiley Periodicals, Inc.
    view abstractdoi: 10.1002/app.38222
  • 2013 • 104 Investigations on diffusion limitations of biocatalyzed reactions in amphiphilic polymer conetworks in organic solvents
    Schoenfeld, I. and Dech, S. and Ryabenky, B. and Daniel, B. and Glowacki, B. and Ladisch, R. and Tiller, J.C.
    Biotechnology and Bioengineering 110 2333-2342 (2013)
    The use of enzymes as biocatalysts in organic media is an important issue in modern white biotechnology. However, their low activity and stability in those media often limits their full-scale application. Amphiphilic polymer conetworks (APCNs) have been shown to greatly activate entrapped enzymes in organic solvents. Since these nanostructured materials are not porous, the bioactivity of the conetworks is strongly limited by diffusion of substrate and product. The present manuscript describes two different APCNs as nanostructured microparticles, which showed greatly increased activities of entrapped enzymes compared to those of the already activating membranes and larger particles. We demonstrated this on the example of APCN particles based on PHEA-l-PDMS loaded with α-Chymotrypsin, which resulted in an up to 28,000-fold higher activity of the enzyme compared to the enzyme powder. Furthermore, lipase from Rhizomucor miehei entrapped in particles based on PHEA-l-PEtOx was tested in n-heptane, chloroform, and substrate. Specific activities in smaller particles were 10- to 100-fold higher in comparison to the native enzyme. The carrier activity of PHEA-l-PEtOx microparticles was tenfold higher with some 25-50-fold lower enzyme content compared to a commercial product. Biotechnol. Bioeng. 2013; 110:2333-2342. © 2013 Wiley Periodicals, Inc.
    view abstractdoi: 10.1002/bit.24906
  • 2013 • 103 Laser-based generation of nanocomposites without matrix-coupling agents for bioactive medical devices
    Schwenke, A. and Wagener, P. and Weiß, A. and Klimenta, K. and Wiegel, H. and Sajti, L. and Barcikowski, S.
    Chemie-Ingenieur-Technik 85 740-746 (2013)
    New production technologies are required to benefit of the full potential of nanocomposites by homogeneous dispersion of nanoparticles along the process chain. Synthesis of silver nanoparticles by laser ablation in liquid and their integration into polymers are presented. Antibacterial properties of these materials and processability into prototypes for medical devices with antibacterial protection are demonstrated. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cite.201200035
  • 2013 • 102 A low-potential glucose biofuel cell anode based on a toluidine blue modified redox polymer and the flavodehydrogenase domain of cellobiose dehydrogenase
    Shao, M. and Pöller, S. and Sygmund, C. and Ludwig, R. and Schuhmann, W.
    Electrochemistry Communications 29 59-62 (2013)
    A pH-dependent, two-electron transfer redox polymer was synthesized based on a methacrylate backbone with tunable properties covalently modified with toluidine blue (P017-TB). Entrapment of the isolated flavodehydrogenase domain of cellobiose dehydrogenase from Myriococcum thermophilum (FAD-MtCDH) within P017-TB is the basis for low-potential bioanode with an open circuit potential of - 240 mV vs. Ag/AgCl and a maximum current density of 60 μA cm - 2 at - 150 mV. Together with a bilirubin oxidase biocathode a biofuel cell with an open circuit voltage of 720 mV and a power density of 6.1 μW cm- 2 was obtained. © 2013 Elsevier B.V.
    view abstractdoi: 10.1016/j.elecom.2013.01.016
  • 2013 • 101 Mutual enhancement of the current density and the coulombic efficiency for a bioanode by entrapping bi-enzymes with Os-complex modified electrodeposition paints
    Shao, M. and Nadeem Zafar, M. and Sygmund, C. and Guschin, D.A. and Ludwig, R. and Peterbauer, C.K. and Schuhmann, W. and Gorton, L.
    Biosensors and Bioelectronics 40 308-314 (2013)
    A bioanode with high current density and coulombic efficiency was developed by co-immobilization of pyranose dehydrogenase from Agaricus meleagris (AmPDH) with the dehydrogenase domain of cellobiose dehydrogenase from Corynascus thermophiles (recDH. CtCDH) expressed recombinantly in Escherichia coli. The two enzymes were entrapped in Os-complex modified electrodeposition polymers (Os-EDPs) with specifically adapted redox potential by means of chemical co-deposition. AmPDH oxidizes glucose at both the C2 and C3 positions whereas recDH. CtCDH oxidizes glucose only at the C1 position. Electrochemical measurements reveal that maximally 6 electrons can be harvested from one glucose molecule at the two-enzyme anode via a cascade reaction, as AmPDH oxidizes the products formed from of the recDH. CtCDH catalyzed substrate oxidation and vice versa. Furthermore, a significant increase in current density can be obtained by combining AmPDH and recDH. CtCDH in a single modified electrode. We propose the use of this bioanode in biofuel cells with increased current density and coulombic efficiency. © 2012 Elsevier B.V.
    view abstractdoi: 10.1016/j.bios.2012.07.069
  • 2013 • 100 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 abstractdoi: 10.1002/mabi.201300219
  • 2013 • 99 Grafting of titanium dioxide microspheres with a temperature-responsive polymer via surface-initiated atom transfer radical polymerization without the use of silane coupling agents
    Smirnov, E.A. and Meledina, M.A. and Garshev, A.V. and Chelpanov, V.I. and Frost, S. and Wieneke, J.U. and Ulbricht, M.
    Polymer International 62 836-841 (2013)
    Titania microspheres with narrow size distribution and diameters of about 1 μm were prepared and subsequently functionalized using surface-initiated atom transfer radical polymerization (ATRP) of N-isopropylacrylamide. The ATRP initiator was immobilized on the particle surface via acylation of surface hydroxyl groups with α-bromoisobutyryl bromide. Subsequently, an established ATRP reaction system was used for the preparation of titania surface-grafted poly(N-isopropylacrylamide) (PNiPAAm). Characterization was performed with electron microscopies, X-ray diffraction, infrared spectroscopy and dynamic light scattering. It was found that the particle size in aqueous dispersions changed reversibly with temperature as expected for a shell of PNiPAAm, a polymer with a lower critical solution temperature at 32 °C. This confirmed the successful preparation of functional, stimuli-responsive TiO2 microparticles via a straightforward controlled surface-initiated polymerization method. © 2012 Society of Chemical Industry.
    view abstractdoi: 10.1002/pi.4377
  • 2013 • 98 Impact of silane and siloxane based hydrophobic powder on cement based mortar
    Spaeth, V. and Lecomte, J.-P. and Delplancke, M.-P. and Orlowsky, J. and Büttner, T.
    Advanced Materials Research 687 100-106 (2013)
    Impact of the addition of silane and siloxane based hydrophobic powders on cement based mortar was studied. Effect of powder addition on mechanical properties and water absorption of cement based mortar is described. Impact of accelerated ageing, including UV radiation, and rain-sun cycles on hydrophobic performance was assessed, demonstrating excellent durability of silane-based hydrophobic performance. © (2013) Trans Tech Publications, Switzerland.
    view abstractdoi: 10.4028/
  • 2013 • 97 High-yield exfoliation of graphite in acrylate polymers: A stable few-layer graphene nanofluid with enhanced thermal conductivity
    Sun, Z. and Pöller, S. and Huang, X. and Guschin, D. and Taetz, C. and Ebbinghaus, P. and Masa, J. and Erbe, A. and Kilzer, A. and Schuhmann, W. and Muhler, M.
    Carbon 64 288-294 (2013)
    High-yield exfoliation of pristine graphite in low boiling point alcohols was achieved using a set of acrylate polymers resulting in few-layer graphene concentrations of up to ∼4 mg mL-1. The polymer showed superior dispersing capabilities for graphene compared to the best reported dispersants, including the solvent N-methyl-pyrrolidone, the surfactants sodium cholate and sodium taurodeoxycholate, and the polymer polyvinylpyrrolidone. The dispersions were stable regardless of freezing (-26 C) or heating (70 C) for 24 h, or dilution with water up to 80% volume ratio over 160 h. The as-obtained nanofluid exhibited an enhancement in thermal conductivity suggesting a great potential in coolant applications. © 2013 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.carbon.2013.07.063
  • 2013 • 96 Cooperative dynamics of microtubule ensembles: Polymerization forces and rescue-induced oscillations
    Zelinski, B. and Kierfeld, J.
    Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 87 (2013)
    We investigate the cooperative dynamics of an ensemble of N microtubules growing against an elastic barrier. Microtubules undergo so-called catastrophes, which are abrupt stochastic transitions from a growing to a shrinking state, and rescues, which are transitions back to the growing state. Microtubules can exert pushing or polymerization forces on an obstacle, such as an elastic barrier, if the growing end is in contact with the obstacle. We use dynamical mean-field theory and stochastic simulations to analyze a model where each microtubule undergoes catastrophes and rescues and where microtubules interact by force sharing. For zero rescue rate, cooperative growth terminates in a collective catastrophe. The maximal polymerization force before catastrophes grows linearly with N for small N or a stiff elastic barrier, in agreement with available experimental results, whereas it crosses over to a logarithmic dependence for larger N or a soft elastic barrier. For a nonzero rescue rate and a soft elastic barrier, the dynamics becomes oscillatory with both collective catastrophe and rescue events, which are part of a robust limit cycle. Both the average and maximal polymerization forces then grow linearly with N, and we investigate their dependence on tubulin on-rates and rescue rates, which can be involved in cellular regulation mechanisms. We further investigate the robustness of the collective catastrophe and rescue oscillations with respect to different catastrophe models. © 2013 American Physical Society.
    view abstractdoi: 10.1103/PhysRevE.87.012703
  • 2013 • 95 N-doped carbon synthesized from N-containing polymers as metal-free catalysts for the oxygen reduction under alkaline conditions
    Zhao, A. and Masa, J. and Muhler, M. and Schuhmann, W. and Xia, W.
    Electrochimica Acta 98 139-145 (2013)
    Nitrogen-doped carbon materials were synthesized and used as metal-free electrocatalysts for the oxygen reduction reaction (ORR) under alkaline conditions. The synthesis was achieved by thermal treatment of nitrogen-containing polymers diluted in different carbon materials. Polypyrrole, polyaniline and polyacrylonitrile were used as N precursors. Carbon black and two types of commercial carbon nanotubes were used as carbon matrices. The obtained N contents were in the range of 1-1.8 wt.%. Different N species including pyridinic, pyrrolic and quaternary N were quantitatively determined by X-ray photoelectron spectroscopy. The ORR activities were evaluated in 0.1 M KOH. Rotating disc electrode studies revealed the presence of multiple active centers in all the samples. The sample obtained using polypyrrole and small diameter nanotubes (ca. 15 nm) had the highest onset potential at -0.07 V vs. Ag/AgCl/3 M KCl, which also showed a significantly higher electrochemical stability than the sample from carbon black and polypyrrole. The ORR activity was not correlated to the total nitrogen amount, but to the amount of pyridinic and quaternary N species. For the onset potential and the (Npyridinic + Nquaternary)/Ntotal ratio a quasi-linear relation was found, which points to the substantial role of pyridinic- and quaternary-N species in ORR catalysis. © 2013 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.electacta.2013.03.043
  • 2012 • 94 Thermal conductivity of polyamide-6,6 in the vicinity of charged and uncharged graphene layers: A molecular dynamics analysis
    Alaghemandi, M. and Gharib-Zahedi, M.R. and Spohr, E. and Böhm, M.C.
    Journal of Physical Chemistry C 116 14115-14122 (2012)
    The thermal conductivity (λ) of nanoconfined polyamide-6,6 (PA) oligomers in polymer-graphene nanocomposites has been investigated by reverse nonequilibrium molecular dynamics (RNEMD) simulations. The preferential alignment of the PA chains parallel to the graphene plane as well as their elongation implies that λ of the polymer in nanocomposites is larger than that in the neat polymer system. The ordering of the polymer phase is enhanced in an arrangement of charged graphene surfaces made of one layer with a charge deficit and one with a charge excess. The consequence of the enhanced polymer ordering as well as the denser packing is an increase in λ in the polymer network. Differences in the thermal conductivity for an armchair and zigzag arrangement of the graphene sheets in the direction of the heat transfer are almost negligible. In contrast with this insensitivity, the present RNEMD simulations predict the largest value of λ for composites with the smallest number of PA chains between adjacent graphene sheets. The modifications in the polymer thermal conductivity are rationalized via several structural parameters such as PA bond orientation relative to the graphene sheets, end-to-end distance of polymer chains, and density profiles. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/jp301452z
  • 2012 • 93 Characterization of the mechanical properties of technical fibers at extreme strain rates
    Bahners, T. and Schloßer, U. and Gutmann, J.
    Macromolecular Materials and Engineering 297 550-558 (2012)
    Technical textiles can be subject to mechanical stress with strain rates far from the quasi-static conditions of common standardized tests. The objective of the presented work was therefore to study the mechanical properties of technical yarns made of PA 6.6, PA 4.6, and PET under strain rates up to 200 s -1, making use of a "falling weight" apparatus. It can be summarized that the moduli at specific points of the stress-strain-curve increase with the strain rate to values up to 50% higher than the data determined under quasi-static strain. Saturation is observed for strain rates larger than 50 s -1. The analysis of failure morphology by scanning electron microscopy revealed molten material at the ends of broken fibers. This indicates thermal failure of the fibers due to local concentration of energy loading. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/mame.201100312
  • 2012 • 92 Photo-initiated lamination of polyethylene (PE) and poly(ethylene terephthalate) (PET)
    Bahners, T. and Gutmann, J.S.
    Journal of Adhesion Science and Technology 26 121-130 (2012)
    Besides plasma-based processes, photo-initiated surface modifications have an interesting potential for adhesion promotion. This is of special interest with applications ranging from classical finishing to composites. Photo-chemical processes using continuous UV sources monochromatic as well as broad band are based on radical activation and ensuing reaction with the atmosphere. Achievable effects are addition of atoms e.g., introduction of oxygen (photo-oxidation) resulting in increased surface energy or grafting of functional groups. Both have certain potentials for adhesion promotion in a physico-chemical way. Based on the fundamental scheme of these processes i.e., a photon-initiated radical reaction at the substrate-atmosphere interface a direct 'inter-linking' of coating polymer and substrate is presented in this paper. The principal idea is to apply a thin layer of coating polymer on the substrate and irradiate this composite system at certain UV wavelengths. Given a low absorption of the radiation by the thin coating and at the same time a high absorption by the substrate, the radiation will penetrate the coating layer and generate radicals at the interface, which will induce cross-linking between the coating polymer and substrate. It is shown that for the example of laminates of polyethylene (PE) film on fabrics made of poly(ethylene terephthalate) (PET), extremely high adhesion strenghths are achieved without any use of additional adhesion promoters. © 2012 Copyright Taylor and Francis Group, LLC.
    view abstractdoi: 10.1163/016942411X569336
  • 2012 • 91 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 &gt; MgSO 4 ≈ NaCl &gt; 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 (&gt;97%) in the range of salt concentrations up to 4 g/L, and only slightly reduced rejection (&gt;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 abstractdoi: 10.1021/am300426c
  • 2012 • 90 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 abstractdoi: 10.1108/13552541211212140
  • 2012 • 89 Solution behavior of double-hydrophilic block copolymers in dilute aqueous solution
    Casse, O. and Shkilnyy, A. and Linders, J. and Mayer, C. and Häussinger, D. and Völkel, A. and Thünemann, A.F. and Dimova, R. and Cölfen, H. and Meier, W. and Schlaad, H. and Taubert, A.
    Macromolecules 45 4772-4777 (2012)
    The self-assembly of double-hydrophilic poly(ethylene oxide)-poly(2-methyl- 2-oxazoline) diblock copolymers in water has been studied. Isothermal titration calorimetry, small-angle X-ray scattering, and analytical ultracentrifugation suggest that only single polymer chains are present in solution. In contrast, light scattering and transmission electron microscopy detect aggregates with radii of ca. 100 nm. Pulsed field gradient NMR spectroscopy confirms the presence of aggregates, although only 2% of the polymer chains undergo aggregation. Water uptake experiments indicate differences in the hydrophilicity of the two blocks, which is believed to be the origin of the unexpected aggregation behavior (in accordance with an earlier study by Ke et al. [Macromolecules2009, 42, 5339-5344]). The data therefore suggest that even in double-hydrophilic block copolymers, differences in hydrophilicity are sufficient to drive polymer aggregation, a phenomenon that has largely been overlooked or ignored so far. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/ma300621g
  • 2012 • 88 Robust mechanical performance of chromium-coated polyethylene terephthalate over a broad range of conditions
    Cordill, M.J. and Taylor, A.A. and Berger, J. and Schmidegg, K. and Dehm, G.
    Philosophical Magazine 92 3346-3362 (2012)
    Mechanical properties of metal films on polymer substrates are normally studied in terms of the fracture and adhesion of the film, while the properties of the polymer substrate and testing conditions are overlooked. Substrate orientation and thickness, as well as strain rate and temperature effects, are examined using Cr films deposited onto polyethylene terephthalate substrates. A faster strain rate affects only the initial fracture strain of the Cr film and not the crack and buckle spacings in the high strain condition. The substrate orientation slightly changes the average crack spacing while the substrate thickness has little effect on the cracking and buckling behaviour. Straining experiments at high temperature increased the average crack spacing and led to a change in buckling mode. The lack of sizeable changes in the mechanical behaviour over the large range of testing procedures leads to a resilient material system for flexible applications. © 2012 Taylor & Francis.
    view abstractdoi: 10.1080/14786435.2012.700418
  • 2012 • 87 Durable press finishing of cotton fabrics with polyamino carboxylic acids
    Dehabadi, V.A. and Buschmann, H.-J. and Gutmann, J.S.
    Carbohydrate Polymers 89 558-563 (2012)
    In this study, a polyamino carboxylic acid was synthesized by reaction of a commercial polyvinylamine and bromoacetic acid. The reaction product was used for crosslinking of cotton fabric by a pad-dry-cure process. Crosslinking of the finished cotton occurred via the formation of ester bonds between the carboxylic groups of the polyamino carboxylic acid and the hydroxyl groups of cellulose. Ester bonds were confirmed by appearance of the corresponding absorbance at 1730 cm -1 in the FTIR spectrum of the finished cotton. The created durable press effect on the finished cotton with polyamino carboxylic acid was evaluated by measuring the wrinkle recovery angle (WRA). Impact of this finishing agent on the physical properties of the cotton was studied by evaluating the tensile strength and whiteness index, and softness of the finished cotton. The easy care effect was durable against laundering. Softness, whiteness, and tensile strength of the finished cotton have not changed significantly. © 2012 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.carbpol.2012.03.047
  • 2012 • 86 Competition between the charge transfer state and the singlet states of donor or acceptor limiting the efficiency in polymer: Fullerene solar cells
    Faist, M.A. and Kirchartz, T. and Gong, W. and Ashraf, R.S. and McCulloch, I. and De Mello, J.C. and Ekins-Daukes, N.J. and Bradley, D.D.C. and Nelson, J.
    Journal of the American Chemical Society 134 685-692 (2012)
    We study the appearance and energy of the charge transfer (CT) state using measurements of electroluminescence (EL) and photoluminescence (PL) in blend films of high-performance polymers with fullerene acceptors. EL spectroscopy provides a direct probe of the energy of the interfacial states without the need to rely on the LUMO and HOMO energies as estimated in pristine materials. For each polymer, we use different fullerenes with varying LUMO levels as electron acceptors, in order to vary the energy of the CT state relative to the blend with [6,6]-phenyl C61-butyric acid methyl ester (PCBM). As the energy of the CT state emission approaches the absorption onset of the blend component with the smaller optical bandgap, E opt,min min{E opt,donor; E opt,acceptor}, we observe a transition in the EL spectrum from CT emission to singlet emission from the component with the smaller bandgap. The appearance of component singlet emission coincides with reduced photocurrent and fill factor. We conclude that the open circuit voltage V OC is limited by the smaller bandgap of the two blend components. From the losses of the studied materials, we derive an empirical limit for the open circuit voltage: V OC ≲ E opt,min/e - (0.66 ± 0.08)eV. © 2011 American Chemical Society.
    view abstractdoi: 10.1021/ja210029w
  • 2012 • 85 Precise hierarchical self-assembly of multicompartment micelles
    Gröschel, A.H. and Schacher, F.H. and Schmalz, H. and Borisov, O.V. and Zhulina, E.B. and Walther, A. and Müller, A.H.E.
    Nature Communications 3 (2012)
    Hierarchical self-assembly offers elegant and energy-efficient bottom-up strategies for the structuring of complex materials. For block copolymers, the last decade witnessed great progress in diversifying the structural complexity of solution-based assemblies into multicompartment micelles. However, a general understanding of what governs multicompartment micelle morphologies and polydispersity, and how to manipulate their hierarchical superstructures using straightforward concepts and readily accessible polymers remains unreached. Here we demonstrate how to create homogeneous multicompartment micelles with unprecedented structural control via the intermediate pre-assembly of subunits. This directed self-assembly leads to a step-wise reduction of the degree of conformational freedom and dynamics and avoids undesirable kinetic obstacles during the structure build-up. It yields a general concept for homogeneous populations of well-defined multicompartment micelles with precisely tunable patchiness, while using simple linear ABC triblock terpolymers. We further demonstrate control over the hierarchical step-growth polymerization of multicompartment micelles into micron-scale segmented supracolloidal polymers as an example of programmable mesoscale colloidal hierarchies via well-defined patchy nanoobjects. © 2012 Macmillan Publishers Limited. All rights reserved.
    view abstractdoi: 10.1038/ncomms1707
  • 2012 • 84 Laser direct writing of high refractive index polymer/TiO 2 nanocomposites
    Guo, Q. and Ghadiri, R. and Xiao, S. and Esen, C. and Medenbach, O. and Ostendorf, A.
    Proceedings of SPIE - The International Society for Optical Engineering 8243 (2012)
    This work reports the preparation of polymer/TiO 2 nanocomposite by adding TiO 2 nanoparticles to the polymer matrices. TiO 2 nanoparticles can be effectively dispersed into the polymer. The refractive index of the nanocomposites can be tuned by increasing the concentration of TiO 2 nanoparticles. The prepared samples exhibit excellent optical transparency in the Vis-NIR region, i.e. at two-photon polymerization (TPP) processing wavelength, and can be used to write threedimensional structures by means of TPP. Structures with high refractive index have been produced with the novel ultrahigh resolution technology based on TPP processing of polymer/TiO 2 nanocomposites. © 2012 SPIE.
    view abstractdoi: 10.1117/12.906688
  • 2012 • 83 Functional plasma polymers deposited in capacitively and inductively coupled plasmas
    Hegemann, D. and Korner, E. and Chen, S. and Benedikt, J. and von Keudell, A.
    Applied Physics Letters 100 051601 (2012)
    Capacitively and inductively coupled plasmas were investigated in order to deposit functional plasma polymers. Considering plasma chemical and surface processes, comparable films can be obtained with both plasma sources yielding distinctly higher deposition rates for ICP. While the gas phase processes scaled with the energy input into the plasma, the surface processes were controlled by the energy dissipated during film growth (ion bombardment). (C) 2012 American Institute of Physics. [doi: 10.1063/1.3681382]
    view abstractdoi: 10.1063/1.3681382
  • 2012 • 82 Membrane fuel cells - Options for bipolar plate materials and production technology
    Heinzel, A. and Kühnemann, L. and Derieth, T. and Grundler, M. and Grimm, T. and Kouachi, M.
    ECS Transactions 50 25-34 (2012)
    Polymer electrolyte membrane fuel cells PEMFC are the type of fuel cell with the broadest range of possible applications, ranging from power supply to electric drives to small scale grid independent power sources and residential CHP units. The technology has been intensively developed for more than two decades and the remaining R&D tasks focus on life time improvement and cost reduction. The following paper will give results on bipolar plate development for PEMFC. © The Electrochemical Society.
    view abstractdoi: 10.1149/05002.0025ecst
  • 2012 • 81 VOC sorption in glassy polyimides-Measurements and modeling
    Hesse, L. and Naeem, S. and Sadowski, G.
    Journal of Membrane Science 415-416 596-607 (2012)
    The sorption behavior of volatile organic compounds (VOCs) in polymeric membrane materials such as polyimide, has a strong effect on the separation efficiency of dense polymeric nanofiltration membranes. To investigate the sorption behavior, this work presents gravimetrically measured and modeled sorption profiles for a series of VOCs (like n-hexane, ethanol, toluene, 2-propanol, and ethyl acetate) in two polyimides (P84 and Matrimid) at 25 °C.The experimental results show significant differences in the sorption speed of the VOCs in the two polyimides. The sorption of toluene, ethyl acetate, and ethanol in Matrimid is very fast compared to the sorption of 2-propanol, but the sorption in P84 is very slow for all the VOCs studied. The sorption behavior of the polyimide/VOC systems has been modeled using an improved one-dimensional Maxwell-Stefan diffusion model. The measured and modeled results provide detailed insight into the specific sorption behavior of the VOCs in the glassy polyimides P84 and Matrimid. © 2012 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2012.05.054
  • 2012 • 80 Modeling liquid-liquid equilibria of polyimide solutions
    Hesse, L. and Sadowski, G.
    Industrial and Engineering Chemistry Research 51 539-546 (2012)
    The mutual affinity of volatile organic compounds (VOCs) and the active polymer layer of dense organic solvent nanofiltration (OSN) membranes is an important property that influences the separation efficiency. Therefore, the affinity between active layer materials and VOCs was investigated by measuring the liquid-liquid equilibria (LLE) between neat polymers used as active layer materials and VOCs. The measured phase equilibria are modeled using the thermodynamic PC-SAFT (perturbed chain statistical associating fluid theory) model. This model allows for estimation of the pressure- and temperature-dependent chemical potentials of VOCs and membrane materials in feeds, membranes, and permeates. Two polyimides (P84 and Matrimid 5218) were selected as typical OSN membrane materials, and five different VOCs (n-hexane, ethyl acetate, 2-propanol, ethanol, and toluene) were considered. It was found that all miscibility gaps between the polyimides and VOCs are open miscibility gaps. The miscibility gaps of Matrimid 5218 and VOCs are much smaller than those of P84 with all VOCs. By means of the PC-SAFT equation of state, the phase behavior of the two polyimides with all considered VOCs could be well described. © 2011 American Chemical Society.
    view abstractdoi: 10.1021/ie2011142
  • 2012 • 79 Stress-induced melting of crystals in natural rubber: A new way to tailor the transition temperature of shape memory polymers
    Heuwers, B. and Quitmann, D. and Katzenberg, F. and Tiller, J.C.
    Macromolecular Rapid Communications 33 1517-1522 (2012)
    Lightly cross-linked natural rubber (NR, cis-1,4-polyisoprene) was found to be an exceptional cold programmable shape memory polymer (SMP) with strain storage of up to 1000%. These networks are stabilized by strain-induced crystals. Here, we explore the influence of mechanical stress applied perpendicular to the elongation direction of the network on the stability of these crystals. We found that the material recovers its original shape at a critical transverse stress. It could be shown that this is due to a disruption of the strain-stabilizing crystals, which represents a completely new trigger for SMPs. The variation of transverse stress allows tuning of the trigger temperature Ttrig(σ) in a range of 45 to 0 °C, which is the first example of manipulating the transition of a crystal-stabilized SMP after programming. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/marc.201200313
  • 2012 • 78 Toward remote-controlled valve functions via magnetically responsive capillary pore membranes
    Himstedt, H.H. and Yang, Q. and Qian, X. and Ranil Wickramasinghe, S. and Ulbricht, M.
    Journal of Membrane Science 423-424 257-266 (2012)
    Polyethyleneterephthalate track-etched membranes with a pore diameter of 650nm were functionalized via surface-initiated atom transfer radical polymerization with grafted poly(2-hydroxyethylmethacrylate). Grafted chain length and density were varied. Superparamagnetic nanoparticles (Fe 3O 4; core diameter 15nm) were selectively covalently coupled to the end groups of the grafted chains. The membranes were characterized by grafting degree, X-ray photoelectron spectroscopy, electron microscopy, zeta potential and pore size in dry state via gas flow/pore dewetting permporometry. The results confirmed that all functionalization steps were well controlled. Water permeability measurements allowed estimation of the hydrodynamic pore diameter of the membranes, and, hence, the hydrodynamic polymer layer thickness on the pore walls. The water permeability of the nanoparticle hybrid membranes was then measured in a static or an alternating external magnetic field. Significant and reversible decreases of permeability were observed, with the largest effects for membranes with high polymer grafting density and long polymer chains (hydrodynamic layer thickness up to 100nm). The maximum change in effective pore diameter was only 6%. However, the estimated change of swollen polymer layer thickness (originally between 60 and 100nm) was up to 13nm. The functionality of the membranes can be tuned by variations of straightforward parameters such as pore size or grafted chain lengths. The study is also relevant as a model system for altering the effective thickness of grafted polymer layers on a surface by an external magnetic field for other applications, for instance in microfluidic systems. © 2012 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2012.08.015
  • 2012 • 77 Micromechanical modeling and strength prediction of short fiber reinforced polymers
    Kaiser, J.-M. and Stommel, M.
    Journal of Polymer Engineering 32 43-52 (2012)
    In this contribution, the embedding and compatibility of commonly used strength criteria in practical engineering design (e.g., Tsai-Hill) into a two-step, mean-field, homogenization approach are investigated. This approach provides the opportunity to account for the heterogeneous microstructure of a polymer composite, caused by the non-unidirectional fiber distribution due to the injection molding process. In a first step, an incremental Mori-Tanaka homogenization scheme is applied to unidirectional sub-domains. In a second step, a Voigt model is used to compute the mechanical composite behavior of an entire domain, which itself is the composition of weighted sub-domains. The chosen two-step approach allows the application of models to predict the strength after both homogenization steps. This leads to two different strength prediction strategies. The selection of certain criteria in combination with the selected level of strength prediction influences the simulation results and the number of material tests necessary for calibration. These two aspects are directly linked to engineering expenses and they are evaluated in a cost benefit analysis. To account for elasto-plasticity, a second-moment formulation is used and extended. The extension allows the direct usage of experimental matrix material data, without having to introduce a virtual matrix as commonly necessary. © 2012 by Walter de Gruyter.
    view abstractdoi: 10.1515/POLYENG.2011.0605
  • 2012 • 76 Temperature analysis of laser heated polymers on microsecond time scales
    Kappes, R.S. and Schönfeld, F. and Li, C. and Gutmann, J.S. and Butt, H.-J.
    Applied Physics A: Materials Science and Processing 106 791-801 (2012)
    To investigate the temperature profiles on laser heated polymer films, we track the thermal radiation with 1 μs time and 1 μm spatial resolution. The resulting two-dimensional temperature graphs are compared to finite element simulations in order to understand the heat conversion and flow. The temperature measurement setup consists of a NIR laser and an optical detection system, which includes high performance optics and a microsecond gated camera, equipped with several interference filters. In this way the thermal radiation is detected in the visible range with spectral resolution. Fitting the spectrum with Planck's law, two-dimensional micrographs of the temperature distribution are obtained. For polystyrene surfaces we were able to analyze the heating and the ablation behavior. Good agreement was found between experimental results and finite element simulations, when ablation is limited to a few tens of nanometers of the film thickness. Ablation of polystyrene starts at 150°C, 50 K above the glass transition temperature. We suggest a photomechanical ablation mechanism at that threshold fluence. For ablation at higher fluence and peak temperature, experiments indicate a thermal decomposition reaction. The temperature range of spinodal decomposition is not reached and can in our case be ruled out as ablation mechanism. © 2011 Springer-Verlag.
    view abstractdoi: 10.1007/s00339-011-6715-3
  • 2012 • 75 The necessity for the coating of perfluorodecalin-filled poly(lactide-co-glycolide) microcapsules in the presence of physiological cholate concentrations: Tetronic-908 as an exemplary polymeric surfactant
    Kirsch, M. and Bramey, T. and Waack, I.N. and Petrat, F. and Mayer, C. and De Groot, H.
    Journal of Microencapsulation 29 30-38 (2012)
    Recently, we demonstrated that biodegradable poly(lactide-co-glycolide) (PLGA) micro- and nanocapsules with a liquid content of perfluorodecalin are principally useful for the development of artificial oxygen carriers. In order to solve a decisive and well-known problem with PLGA microcapsules, i.e. the spontaneous agglomeration of the capsules after depletion of the emulsifying agent (i.e. cholate), coating with the ABA block copolymer, Tetronic-908 was studied. After Tetronic-908 treatment at concentrations that were harmless to cultured cells, the clustering of the microcapsules was prevented, the adsorption of opsonins was decreased and the attachment to cells was inhibited, but the oxygen transport capacity of PLGA microcapsules was even increased. The present data clearly show that perfluorodecalin-filled PLGA microcapsules must be coated before decreasing the emulsifying agent cholate to physiological concentrations, in order to develop a solution that has the capabilities to function as a potential artificial oxygen carrier suspension. © 2012 Informa UK Ltd All rights reserved.
    view abstractdoi: 10.3109/02652048.2011.629743
  • 2012 • 74 The multiscale approach to the curing of polymers incorporating viscous and shrinkage effects
    Klinge, S. and Bartels, A. and Steinmann, P.
    International Journal of Solids and Structures 49 3883-3900 (2012)
    This contribution deals with the modeling of viscoelastic and shrinkage effects accompanying the curing of polymers at multiple length scales. For the modeling of viscous effects, the deformation at the microlevel is decomposed into an elastic and a viscoelastic part, and a corresponding energy density consisting of equilibrium and non-equilibrium parts is proposed. The former is related to the total deformation; it has the form of a convolution integral and depends on the time evolution of the material parameters. The non-equilibrium part depends on the elastic part of deformations only. The material parameters are constant in time, thus an integral form is not necessary. In contrast to the viscous effects, the modeling of shrinkage effects does not require any further extension of the expression for the energy density, but an additional decomposition of the deformation into a shrinkage and a mechanical part. Since the material compressibility is taken into consideration, a multifield formulation is applied for the equilibrium as well as for the non-equilibrium energy part. As a final aspect, the paper includes a study of macroheterogenous polymers for whose modeling the multiscale finite element method is applied. Within this numerical approach, a macroscopic body is treated as a homogeneous body whose effective properties are evaluated on the basis of the simulations which are carried out at the level of the representative volume element. The application of the model proposed is illustrated on the basis of examples studying the influence of individual parameters on the stress state as well as the influence of the volume fraction of different phases at the microscale on the effective material behavior. © 2012 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.ijsolstr.2012.08.016
  • 2012 • 73 Modeling of curing processes based on a multi-field potential. Single- and multiscale aspects
    Klinge, S. and Bartels, A. and Steinmann, P.
    International Journal of Solids and Structures 49 2320-2333 (2012)
    This paper provides a continuum mechanical model for the curing of polymers, including the incompressibility effects arising at the late stages of the process. For this purpose, the free energy density functional is split into a deviatoric and a volumetric part, and a multifield formulation is inserted. An integral formulation of the functional is used to depict the time-dependent material behavior. The model is also coupled with the multiscale finite element method, a numerical approach serving for the modeling of heterogeneous materials with a highly oscillatory microstructure. The effects of the proposed extensions are illustrated on the basis of several numerical examples concerned with the study of the influence of Poisson's ratio on the curing process and the behavior of the microheterogeneous polymers. © 2012 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.ijsolstr.2012.04.034
  • 2012 • 72 Organosoluble enzyme conjugates with poly(2-oxazoline)s via pyromellitic acid dianhydride
    Konieczny, S. and Fik, C.P. and Averesch, N.J.H. and Tiller, J.C.
    Journal of Biotechnology 159 195-203 (2012)
    The use of enzymes in organic solvents offers a great opportunity for the synthesis of complex organic compounds and is therefore in focus of current research. In this work we describe the synthesis of poly(2-methyl-1,3-oxazoline) (PMOx) and poly(2-ethyl-1,3-oxazoline) (PEtOx) enzyme conjugates with hen-egg white lysozyme, RNase A and α-chymotrypsin using a new coupling technique. The POXylation was carried out reacting pyromellitic acid dianhydride subsequently with ethylenediamine terminated POx and then with the NH 2-groups of the respective enzymes. Upon conjugation with the polymers, RNase A and lysozyme became fully soluble in DMF (1.4mg/ml). These are the first examples of fully POXylated proteins, which become organosoluble. The synthesized enzyme conjugates were characterized by SDS-PAGE, isoelectric focusing, dynamic light scattering and size exclusion chromatography, which all indicated the full POXylation of the enzymes. The modified enzymes even partly retained their activity in water. With α-chymotrypsin as example we could demonstrate that the molecular weight of the attached polymer significantly influences the activity. © 2012 Elsevier B.V.
    view abstractdoi: 10.1016/j.jbiotec.2012.01.016
  • 2012 • 71 Well-defined amphiphilic poly(2-oxazoline) ABA-triblock copolymers and their aggregation behavior in aqueous solution
    Krumm, C. and Fik, C.P. and Meuris, M. and Dropalla, G.J. and Geltenpoth, H. and Sickmann, A. and Tiller, J.C.
    Macromolecular Rapid Communications 33 1677-1682 (2012)
    Self-organization of block copolymers in solution is a way to obtain advanced functional superstructures. The synthesis of well-defined polymethyloxazoline-block-polyphenyloxazoline-block-polymethyloxazoline triblock copolymers is described and proven by 1H NMR spectroscopy, SEC, and ESI-MS. The surprisingly water- soluble block copolymers do self-organize in aqueous solutions uniquely forming three coexisting well-defined structures: unimolecular micelles, micellar aggregates, and very form-stable polymersomes. This is the first example of a polymersome forming ABA-triblock copolymer with a glassy middle block. The spherical vesicles are analysed by scanning electron microscopy and transmission electron microscopy. It could be shown that these vesicles are indeed hollow spheres. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/marc.201200192
  • 2012 • 70 Mechanisms of crazing in glassy polymers revealed by molecular dynamics simulations
    Mahajan, D.K. and Hartmaier, A.
    Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 86 (2012)
    Mechanisms leading to initiation of crazing type failure in a glassy polymer are not clearly understood. This is mainly due to the difficulty in characterizing the stress state and polymer configuration sufficiently locally at the craze initiation site. Using molecular dynamics simulations, we have now been able to access this information and have shown that the local heterogeneous deformation leads to craze initiation in glassy polymers. We found that zones of high plastic activity are constrained by their neighborhood and become unstable, initiating crazing from these sites. Furthermore, based on the constant flow stresses observed in the unstable zones, we conclude that microcavitation is the essential local deformation mode to trigger crazing in glassy polymers. Our results demonstrate the basic difference in the local deformation mode as well as the conditions that lead to either shear-yielding or crazing type failures in glassy polymers. We anticipate our paper to help in devising a new criterion for craze initiation that not only considers the stress state, but also considers local deformation heterogeneities that form the necessary condition for crazing in glassy polymers. © 2012 American Physical Society.
    view abstractdoi: 10.1103/PhysRevE.86.021802
  • 2012 • 69 Performance of fluorene and terthiophene copolymer in bilayer photovoltaic devices: The role of the polymer conformations
    Marchiori, C.F.N. and Yamamoto, N.A.D. and Grova, I.R. and MacEdo, A.G. and Paulus, M. and Sternemann, C. and Huotari, S. and Akcelrud, L. and Roman, L.S. and Koehler, M.
    Organic Electronics: physics, materials, applications 13 2716-2726 (2012)
    We report experiments using fluorene and terthiophene copolymer as the active layer in bilayer devices with C 60. The highest short circuit current, open circuit voltage and power conversion efficiency upon AM1.5 illumination were 6.8 mA/cm 2, 0.68 V and 2.33%, respectively. Density functional theory analysis was used to identify the most stable configurations of the terthiophene moieties in the polymer: the most stable form has the thiophene rings in the alternate configuration (anti) and the second conformation has the thiophene rings pointing to the same direction (syn). Comparing theoretical results with measurements of absorbance, X-ray diffraction, and X-ray reflectometry experiments, we conclude that the annealing treatment produces conformational anti to syn transition along the backbone of poly[9,9′-n-dihexyl-2,7-fluorene-alt-2,5-terthiophene] (LaPPS45). The syn segments of the chain condensed then in a lamellar ordered structure which increases the degree of crystallinity of the annealed samples and improve the light harvest at long wavelengths. From absorption measurements of films submitted to different annealing temperatures and with the help of theoretical calculations we propose a "wave-like" aggregation pattern to the syn segments in those lamellas. © 2012 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.orgel.2012.08.002
  • 2012 • 68 Synthesis of hybrid microgels by coupling of laser ablation and polymerization in aqueous medium
    Nachev, P. and Van 'T Zand, D.D. and Coger, V. and Wagener, P. and Reimers, K. and Vogt, P.M. and Barcikowski, S. and Pich, A.
    Journal of Laser Applications 24 (2012)
    Loading microgels with bioactive nanoparticles (NPs) often requires multiple synthesis and purification steps, and organic solvents or precursors that are difficult to remove from the gel. Hence, a fast and aqueous synthesis procedure would facilitate the synthesis of inorganic-organic hybrid microgels. Two microgel compounds were hybridized with laser-generated zinc oxide (ZnO) NPs prepared in a single-step procedure. ZnO NPs were formed by laser ablation in liquid, while the polymer microgels were synthesized in-situ inside the ablation chamber. Further, the authors report the preparation of two different microgel systems. The first one was produced without the use of chemical initiator forming hydrogels with ZnO NPs and diffuse morpholgy. Typical microgel colloids were also synthesized via a conventional chemical method in a preheated reaction chamber. The existence of microgel colloids partially loaded with ZnO NPs was confirmed in a transmission electron microscopy investigation. Fourier transform infrared spectroscopic measurements and dynamic light scattering verify the formation of polymer colloids. These initial results indicate the application potential of laser ablation in microgel precursor solution for the fabrication of polymeric carriers for inorganic nanoparticles. Preliminary biological tests using zinc chloride demonstrated negative dose effects on primary cell culture with zinc concentrations above 200 μM but no noticeable influence at 100 μM. © 2012 Laser Institute of America.
    view abstractdoi: 10.2351/1.4730803
  • 2012 • 67 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 abstractdoi: 10.1021/ma2025286
  • 2012 • 66 Development of a group contribution method for polymers within the PC-SAFT model
    Peters, F.T. and Laube, F.S. and Sadowski, G.
    Fluid Phase Equilibria 324 70-79 (2012)
    Based on the PC-SAFT equation of state (EOS) a group contribution method (GCM) for polymers is developed to describe thermodynamic properties of the pure polymers as well as binary (co-)polymer/solvent liquid-liquid phase equilibria (LLE). The polymer parameters are obtained from group contributions by applying simple arithmetic and geometric mixing rules. Polymer classes of poly(olefines), poly(acrylates) as well as poly(methacrylates) are considered leading to the parameter set for five specific groups CH 3, &gt;CH 2, &gt;(CH) and &gt;C< as well as the (CO)O group. The modeling approach is applied to pure polymer density and binary LLE data. Modeling results using the GCM polymer parameters are found to be in good agreement with experimental literature data. © 2012 Elsevier B.V.
    view abstractdoi: 10.1016/j.fluid.2012.03.009
  • 2012 • 65 A new synthesis route for Os-complex modified redox polymers for potential biofuel cell applications
    Pöller, S. and Beyl, Y. and Vivekananthan, J. and Guschin, D.A. and Schuhmann, W.
    Bioelectrochemistry 87 178-184 (2012)
    A new synthesis route for Os-complex modified redox polymers was developed. Instead of ligand exchange reactions for coordinative binding of suitable precursor Os-complexes at the polymer, Os-complexes already exhibiting the final ligand shell containing a suitable functional group were bound to the polymer via an epoxide opening reaction. By separation of the polymer synthesis from the ligand exchange reaction at the Os-complex, the modification of the same polymer backbone with different Os-complexes or the binding of the same Os-complex to a number of different polymer backbones becomes feasible. In addition, the Os-complex can be purified and characterized prior to its binding to the polymer. In order to further understand and optimize suitable enzyme/redox polymer systems concerning their potential application in biosensors or biofuel cells, a series of redox polymers was synthesized and used as immobilization matrix for Trametes hirsuta laccase. The properties of the obtained biofuel cell cathodes were compared with similar biocatalytic interfaces derived from redox polymers obtained via ligand exchange reaction of the parent Os-complex with a ligand integrated into the polymer backbone during the polymer synthesis. © 2011 Elsevier B.V.
    view abstractdoi: 10.1016/j.bioelechem.2011.11.015
  • 2012 • 64 Antimicrobial polymers in solution and on surfaces: Overview and functional principles
    Siedenbiedel, F. and Tiller, J.C.
    Polymers 4 46-71 (2012)
    The control of microbial infections is a very important issue in modern society. In general there are two ways to stop microbes from infecting humans or deteriorating materials-disinfection and antimicrobial surfaces. The first is usually realized by disinfectants, which are a considerable environmental pollution problem and also support the development of resistant microbial strains. Antimicrobial surfaces are usually designed by impregnation of materials with biocides that are released into the surroundings whereupon microbes are killed. Antimicrobial polymers are the up and coming new class of disinfectants, which can be used even as an alternative to antibiotics in some cases. Interestingly, antimicrobial polymers can be tethered to surfaces without losing their biological activity, which enables the design of surfaces that kill microbes without releasing biocides. The present review considers the working mechanisms of antimicrobial polymers and of contact-active antimicrobial surfaces based on examples of recent research as well as on multifunctional antimicrobial materials. © 2012 by the authors; licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/polym4010046
  • 2012 • 63 Simulation of the long term behaviour of plastics components
    Stommel, M. and Naumann, T.
    Macromolecular Symposia 311 92-97 (2012)
    This paper presents a method to model the mechanical behavior of polymers over a wide time- and load-range by means of finite element analyses. The method includes a material model as well as the determination of material parameters to calibrate the material model. As a special feature of this method the model is calibrated only by using creep data that are commonly available in material data bases. So the procedure improves the simulation of the long time behavior of plastic-components without an additional experimental effort. In combination with time-temperature-superposition principle, the temperature dependency of the long term behavior is represented, too. The simulation results are validated by creep experiments on an example part. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/masy.201000099
  • 2012 • 62 Tailored star-shaped statistical teroligomers via ATRP for lithographic applications
    Wieberger, F. and Forman, D.C. and Neuber, C. and Gröschel, A.H. and Böhm, M. and Müller, A.H.E. and Schmidt, H.-W. and Ober, C.K.
    Journal of Materials Chemistry 22 73-79 (2012)
    A series of five star-shaped teroligomers consisting of a saccharose core, and arms, composed of α-gamma butyrolactone methacrylate (GBLMA), methyl adamantyl methacrylate (MAMA) and hydroxyl adamantyl methacrylate (HAMA) with defined arm length and number of arms were prepared via the core-first atom transfer radical polymerization (ATRP) route. The saccharose core was modified with ATRP initiating sites and non-reactive sites, enabling the synthesis of star polymers with a smaller arm number but identical core. Star teroligomers were synthesized with narrow molecular weight distributions with low polydispersity indices (PDIs < 1.1) showing negligible side reactions only at higher conversions of Xp &gt; 50%. The absence of side reaction and the precise achievement of the target molecular weight indicated excellent control over the reaction. A selected star-shaped teroligomer was investigated for the first time as a photoresist material. The delicate conditions of the lithographic process were optimized by a combinatorial approach. The obtained low line edge and line width roughness of the observed pattern demonstrate the potential of the star architecture for this application.
    view abstractdoi: 10.1039/c1jm11922b
  • 2012 • 61 Novel membrane adsorbers with grafted zwitterionic polymers synthesized by surface-initiated ATRP and their salt-modulated permeability and protein binding properties
    Yang, Q. and Ulbricht, M.
    Chemistry of Materials 24 2943-2951 (2012)
    A novel zwitterionic polymer functionalized porous membrane adsorber was obtained by grafting poly(N,N-dimethyl-N-methacryloyloxyethyl-N-(3-sulfopropyl) ammonium betaine) (polySPE) to poly(ethylene terephthalate) (PET) track-etched membrane surface via surface-initiated atom transfer radical polymerization (SI-ATRP). The ATRP conditions were optimized, the thus established grafting was well-controlled, and the degree of grafting could be adjusted. Functionalized membranes with a degree of grafting of about 3.5 μg/cm 2 relative to the specific surface area showed almost zero values of zeta potential estimated from the trans-membrane streaming potential measurements. Typical "anti-polyelectrolyte" effect was observed for the polySPE grafted membranes. Flux through the membrane was reduced by adding chaotropic chloride and perchlorate salts to the solution which extended the polySPE chains grafted on the membrane pore wall. Perchlorate salt exhibited much stronger effect on polySPE chain conformation than chloride salt and for a membrane with a degree of grafting of 2.7 μg/cm 2, even 2 mM KClO 4 could extend the thickness of the polymer layer to more than two times (∼43 nm) of that in pure water (∼20 nm). On the contrary, small amounts of kosmotropic ions (10 mM SO 4 2-) further "salted out" the polySPE chains and led to a slightly increased flux. PolySPE grafted PET membranes with different degree of grafting were then used as membrane adsorber for protein binding. Human IgG was used as model protein and the binding capacity was evaluated under both static (no convective flow through the membrane) and dynamic conditions (flow-through conditions). Static adsorption experiments showed that IgG could be loaded to the membrane at medium salt concentration and 85-95% of bound protein could be eluted at either low (zero) or very high salt concentrations. Dynamic flow-through experiments then revealed the influences of salt concentration and salt type on IgG binding. Effects of two chaotropic salts, NaCl and NaClO 4, were evaluated. Slight but not negligible binding of IgG from pure water was suppressed by adding NaCl. IgG binding was then increased in the NaCl concentration range of 100-500 mM and reached a maximum binding capacity value at about 500 mM. Further increase of NaCl concentration led to a decreased binding again. KClO 4 showed similar effects onto IgG binding, but this salt functions in a much lower and much narrower concentration range. All results with respect to grafted layer swelling and protein binding followed the empirical Hofmeister series. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/cm301116p
  • 2011 • 60 Probing the intrinsic switching kinetics of ultrathin thermoresponsive polymer brushes
    Amiri Naini, C. and Franzka, S. and Frost, S. and Ulbricht, M. and Hartmann, N.
    Angewandte Chemie - International Edition 50 4513-4516 (2011)
    Laser-stimulated polymer brushes: The temperature-dependent switching kinetics of surface-grafted thermoresponsive polymer brushes were investigated by a stroboscopic micromanipulation/-characterization technique for real-time parallel measurements (see picture). Intrinsic response times range from the microsecond to the millisecond time scale; these results could lead to fabrication of nanosized polymeric actuators and sensors with unprecedented responsivities. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201100140
  • 2011 • 59 Influence of alkyl chain length and molecular weight on the surface functionalization via adsorption/entrapment with biocidal cationic block copolymers
    Berndt, E. and Behnke, S. and Ulbricht, M.
    European Polymer Journal 47 2379-2390 (2011)
    Polysulfone (PSf) films were functionalized with block copolymers containing poly(n-butyl acrylate) (PBA) as anchor block which is able to firmly tether the biocidal quaternized poly(2-dimethylaminoethyl methacrylate) (PDMAEMAq) to the surface. Block copolymers were synthesized using sequential atom transfer radical polymerization (ATRP) and quaternization with methyl and/or octyl groups rendered the polymers biocidal. Upon reversible swelling of the PSf surface layer in the adsorption/entrapment process, incorporation of the block copolymer is anticipated to be stable; homopolymers, i.e., methyl- or octyl-quaternized PDMAEMAq, were investigated for comparison. The addition of salt to the functionalization solution containing the block copolymer induced a decrease in the critical micelle concentration and lead to higher functionalization efficiency. The impact of intra- or interchain interactions in these aggregates on adsorption and firm entrapment in PSf was determined by measuring contact angle, charge density and zeta potential. © 2011 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.eurpolymj.2011.09.019
  • 2011 • 58 A chloride resistant high potential oxygen reducing biocathode based on a fungal laccase incorporated into an optimized Os-complex modified redox hydrogel
    Beyl, Y. and Guschin, D.A. and Shleev, S. and Schuhmann, W.
    Electrochemistry Communications 13 474-476 (2011)
    A chloride-resistant high-potential biocathode based on Trametes hirsuta laccase incorporated into an optimized Os-complex modified redox hydrogel (80 mV potential difference to the T1 Cu) is described. The bioelectrocatalytic activity towards O 2 reduction is due to an intimate access of the polymer-bound Os-complex to the T1 Cu site. The chloride resistance of the biocathode is due to the tight binding of the polymer-bound Os-complex to the T1 Cu site. © 2011 Elsevier B.V.
    view abstractdoi: 10.1016/j.elecom.2011.02.024
  • 2011 • 57 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 abstractdoi: 10.1002/mabi.201000306
  • 2011 • 56 Comparative studies on thermomechanical behavior of veriflex, a shape memory polymer, for a low strain (m = 70%): Laser experiments
    Chowdhury, A.M.S. and Schmidt, C. and Neuking, K. and Eggeler, G.
    Journal of Macromolecular Science, Part A: Pure and Applied Chemistry 48 707-712 (2011)
    An interesting comparative case study on thermomechanical cycles including programming, cooling, unloading and heating to trigger the 1WE was done using Veriflex at 62C (T Tg close to and below 5C of Tg) and also at 72C (T Tg, close to and above 5C of Tg) for slightly low strains (m = 70%) and the recovery time of 10 min. Accumulation of strain was estimated during the thermomechanical treatments for using both 70% strains at 62C (T Tg), as well as at 72C (T Tg). Recovery ratios for 70% strains at 62C (T Tg), as well as for 72C (T Tg) were also estimated. It turns out that programming, cooling, unloading and heating to trigger the 1WE causes an increase of irreversible strain and is associated with a corresponding decrease of the intensity of the 1WE, in particular, during the first thermomechanical cycles. A LSCM (Laser Scanning Confocal Microscopic) study shows very little change in surface structure which evolved during cycling up to 70% strains at 72C (T Tg). © Taylor & Francis Group, LLC.
    view abstractdoi: 10.1080/10601325.2011.596049
  • 2011 • 55 Interface failure and adhesion measured by focused ion beam cutting of metal-polymer interfaces
    Cordill, M.J. and Schmidegg, K. and Dehm, G.
    Philosophical Magazine Letters 91 530-536 (2011)
    New developments in flexible electronics require metal films to adhere to polymer substrates. Measuring the interfacial adhesion of these systems is challenging, requiring the formulation of new techniques and models. A strategy to measure the adhesion of Cr-polyethylene terephthalate (PET) interfaces using tensile straining and buckle formation is presented in this article. Focused ion beam cross-sectioning of the buckles reveals that the polymer substrate can locally fail, which may lead to an overestimate of adhesion. Cr-PET adhesion energy of 9.4±1.6 J/m2 is determined with the present approach. © 2011 Taylor &Francis.
    view abstractdoi: 10.1080/09500839.2011.593575
  • 2011 • 54 Microstructure and adhesion of as-deposited and annealed Cu/Ti films on polyimide
    Cordill, M.J. and Taylor, A. and Schalko, J. and Dehm, G.
    International Journal of Materials Research 102 729-734 (2011)
    The ability to measure the adhesion energy of metal thin films on polymer substrates is important for the design of reliable flexible electronic devices. One technique is to create well-defined areas of delamination (buckles) as a consequence of lateral compressive stresses induced by tensile straining of the film-substrate system. The adhesion energy is calculated from the buckle dimensions. In order to improve the adhesion between the metal film and polymer substrate, thin adhesion layers can be incorporated. However, interdiffusion and reactions can occur between the adhesion layer and the metal film when subjected to elevated temperatures. This is detrimental for the interfacial adhesion, as will be discussed for Cu films on polyimide with a Ti interlayer subjected to annealing at 350°C. © Carl Hanser Verlag GmbH & Co. KG.
    view abstractdoi: 10.3139/146.110513
  • 2011 • 53 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 abstractdoi: 10.1021/bm200476g
  • 2011 • 52 Switchable supramolecular polymers from the self-assembly of a small monomer with two orthogonal binding interactions
    Gröger, G. and Meyer-Zaika, W. and Böttcher, C. and Gröhn, F. and Ruthard, C. and Schmuck, C.
    Journal of the American Chemical Society 133 8961-8971 (2011)
    The low molecular weight heteroditopic monomer 1 forms supramolecular polymers in polar solution as shown, for example, by infrared laser-based dynamic light scattering (DLS), small-angle neutron scattering (SANS), electron microscopy (TEM, cryo-TEM), and viscosity measurements. Self-assembly of 1 is based on two orthogonal binding interactions, the formation of a Fe(II)-terpyridine 1:2 metal-ligand complex and the dimerization of a self-complementary guanidiniocarbonyl pyrrole carboxylate zwitterion. Both binding interactions have a sufficient stability in polar (DMSO) and even aqueous solutions to ensure formation of linear polymers of considerable length (up to 100 nm). The supramolecular polymerization follows a ring-chain mechanism causing a significant increase in the viscosity of the solutions at millimolar concentrations and above. The linear polymers then further aggregate in solution into larger globular aggregates with a densely packed core and a loose shell. Both binding interactions can be furthermore switched on and off either by adding a competing ligand to remove the metal ion and subsequent readdition of Fe(II) or by reversible protonation and deprotonation of the zwitterion upon addition of acid or base. The self-assembly of 1 can therefore be switched back and forth between four different states, the monomer, a metal-complexed dimer or an ion paired dimer, and finally the polymer. © 2011 American Chemical Society.
    view abstractdoi: 10.1021/ja200941a
  • 2011 • 51 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 abstractdoi: 10.1016/j.memsci.2011.02.018
  • 2011 • 50 Flexibility and sorption selectivity in rigid metal-organic frameworks: The impact of ether-functionalised linkers (Chemistry - A European Journal (2010) (16))
    Henke, S. and Schmid, R. and Grunwaldt, J.-D. and Fischer, R.A.
    Chemistry - A European Journal 17 411 (2011)
    doi: 10.1002/chem.201190003
  • 2011 • 49 Magnetically activated micromixers for separation membranes
    Himstedt, H.H. and Yang, Q. and Dasi, L.P. and Qian, X. and Wickramasinghe, S.R. and Ulbricht, M.
    Langmuir 27 5574-5581 (2011)
    Presented here is a radically novel approach to reduce concentration polarization and, potentially, also fouling by colloids present in aqueous feeds: magnetically responsive micromixing membranes. Hydrophilic polymer chains, poly(2-hydroxyethyl methacrylate) (PHEMA), were grafted via controlled surface-initiated atom transfer radical polymerization (SI-ATRP) on the surface of polyamide composite nanofiltration (NF) membranes and then end-capped with superparamagnetic iron oxide magnetite (Fe3O4) nanoparticles. The results of all functionalization steps, that is, bromide ATRP initiator immobilization, SI-ATRP, conversion of PHEMA end groups from bromide to amine, and carboxyl-functional Fe3O4 nanoparticle immobilization via peptide coupling, have been confirmed by X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FESEM). These nanoparticles experience a magnetic force as well as a torque under an oscillating external magnetic field. It has been shown, using particle image velocimetry (PIV), that the resulting movement of the polymer brushes at certain magnetic field frequencies induces mixing directly above the membrane surface. Furthermore, it was demonstrated that with such membranes the NF performance could significantly be improved (increase of flux and salt rejection) by an oscillating magnetic field, which can be explained by a reduced concentration polarization in the boundary layer. However, the proof-of-concept presented here for the active alteration of macroscopic flow via surface-anchored micromixers based on polymer-nanoparticle conjugates has much broader implications. © 2011 American Chemical Society.
    view abstractdoi: 10.1021/la200223g
  • 2011 • 48 Facile synthesis of triblock co- and terpolymers of styrene, 2-vinylpyridine, and methyl methacrylate by a new methodology combining living anionic diblock copolymers with a specially designed linking reaction
    Hirao, A. and Matsuo, Y. and Oie, T. and Goseki, R. and Ishizone, T. and Sugiyama, K. and Gröschel, A.H. and Müller, A.H.E.
    Macromolecules 44 6345-6355 (2011)
    Triblock co- and terpolymers with orders of blocks synthetically difficult to be obtained by means of sequential living anionic polymerization were successfully synthesized by developing a new methodology combining living anionic block copolymers with a specially designed linking reaction. The synthesized polymers involve ACB and BAC triblock terpolymers and ABA′, ACA′, and BCB′ triblock copolymers, where A, B, and C are polystyrene, poly(2-vinylpyridine), and poly(methyl methacrylate) segments, respectively. The A′, A as well as B, B′ are identical in polymer structure but different in molecular weight. All of them are new type triblock ter- and copolymers with well-defined structures, i.e., predictable molecular weights, compositions, and narrow molecular weight distributions. Transmission electron microscopic studies were performed on bulk morphologies of ACB and BAC triblock terpolymers to exemplarily investigate the influence of changing block sequence and thus changing interfaces. Although both terpolymers showed the tendency to form a lamella-lamella morphology, ACB revealed unusually strongly curved lamellae and BAC even undulated lamellae. © 2011 American Chemical Society.
    view abstractdoi: 10.1021/ma201352z
  • 2011 • 47 Polythiophene-assisted vapor phase synthesis of carbon nanotube-supported rhodium sulfide as oxygen reduction catalyst for HCl electrolysis
    Jin, C. and Nagaiah, T.C. and Xia, W. and Bron, M. and Schuhmann, W. and Muhler, M.
    ChemSusChem 4 927-930 (2011)
    Rhodium Drive: Carbon nanotube-supported rhodium sulfide electrocatalysts are prepared by sequential chemical vapor deposition of iron, controlled vapor phase polymerization of thiophene, and finally impregnation of the rhodium precursor and pyrolysis. The electrocatalysts are applied in the oxygen reduction reaction under HCl electrolysis conditions. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cssc.201000315
  • 2011 • 46 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 abstractdoi: 10.1021/ma1021715
  • 2011 • 45 Miniaturized based on oxygen diffusion timing sensor for polymer packaging
    Marek, P. and Velasco-Velez, J.J. and Haas, T. and Doll, T. and Sadowski, G.
    Procedia Engineering 25 1217-1220 (2011)
    A non-electronic lifetime indicator for packaging has been developed using a colour reaction and diffusion in microchannels. It uses oxygen uptake in polymers after an originality seal is broken by manipulation or regular opening. The oxygen triggers a colour change that is made visible after desired timing period at corresponding diffusion lengths. This timing sensor was realized within a microchannel suitable for packaging cap. Rigorous design was based on modeling the diffusion - reaction equation and experimentally determined diffusion coefficients. To achieve appropriate functionality, temperature effects must be compensated using nanofunctioned materials as well as substrate diffusion of other gases like water. The methodology and design rules are generalized for microfluidics packaging. © 2011 Published by Elsevier Ltd.
    view abstractdoi: 10.1016/j.proeng.2011.12.300
  • 2011 • 44 Polymerisation of butyl acrylate in the two phase slug flow regime of parallel microcapillary reactors
    Mendorf, M. and Moenter, A. and Moll, T. and Agar, D.W. and Tiller, J.
    Macromolecular Symposia 302 245-256 (2011)
    Summary: The potential and problems of conducting a free radical polymerisation in parallel capillary reactors are presented. By operating in the so-called slug flow regime of immiscible liquid-liquid flow, one can achieve perfectly uniform residence times which are inaccessible using single phase flow. The excellent performance available in microreactors can be exploited for higher throughputs through the simple expedient of numbering-up, i.e. operation of multiple similar reactors in parallel under identical hydrodynamic conditions. In practice this approach often comes to grief on the coupling between hydrodynamics and chemical reaction, for example due to the strong influence of polymerisation on viscosity. Rigorous modeling reveals that the operating conditions sought are actually unstable. Furthermore, the uniformity of flow distribution between parallel capillaries was found to be very sensitive to the manufacturing tolerances of the capillaries used in the presence of polymerisation. Two strategies for resolving such problems are discussed. In the first case, coupling between reaction and the flow distribution is suppressed by a sufficiently high pressure drop upstream of the temperature regulated reactor segments. The pressure drop necessary to achieve this decoupling was estimated by the model. An alternative technique involves an appropriately inexpensive flow control system for each individual capillary. Since commercially available microvalves and flow measurement equipment are too costly for parallelisation purposes, it is necessary to develop new components to fulfill these functions. An optical monitoring technique is presented that meets both the technical and economic criteria, and which can be readily combined with recently developed new micro valves.1 © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/masy.201000067
  • 2011 • 43 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 abstractdoi: 10.1088/0953-8984/23/18/184111
  • 2011 • 42 PePC-SAFT: Modeling of polyelectrolyte systems 2. Aqueous two-phase systems
    Naeem, S. and Sadowski, G.
    Fluid Phase Equilibria 306 67-75 (2011)
    This work considers aqueous two-phase systems (ATPS) containing one polymer-polyelectrolyte as well as one salt. To model the liquid-liquid equilibria (LLE) of these systems, the recently presented model pePC-SAFT has been employed. ATPS containing poly(acrylic acid) of different degrees of neutralization or poly(vinyl pyrrolidone), respectively, were considered. The binary interaction parameters used between water-poly(acrylic acid) and water-poly(vinyl pyrrolidone) were adjusted to vapor-liquid equilibrium (VLE) data of these systems. ATPS consisting of poly(vinyl pyrrolidone)-water-sodium sulfate were predicted as function of temperature as well as of molar mass of the polymer. For poly(acrylic acid) systems, ATPS were predicted as function of charge density (degree of neutralization) for different types of salt. For these calculations, the polyelectrolyte model parameters were determined from the non-charged polymer whereas the effect of increasing charge density has been purely predicted by the model. Using this approach, it is possible to predict the shrinking of the liquid-liquid equilibrium region with increasing charging of the polyelectrolyte. © 2011 Elsevier B.V.
    view abstractdoi: 10.1016/j.fluid.2011.02.024
  • 2011 • 41 Nanowear in a nanocomposite reinforced polymer
    Pihan, S.A. and Emmerling, S.G.J. and Butt, H.-J. and Gutmann, J.S. and Berger, R.
    Wear 271 2852-2856 (2011)
    We investigated the reinforcement of blends made from poly(ethyl methacrylate) (PEMA) and PEMA-grafted nanoparticles at a nanometer length scale. The reinforcement was probed by nanowear experiments based on scanning force microscopy (SFM). In addition to imaging, the SFM is applied to wear the surface of samples at the length scale of nanoparticles. Blends with different miscibility of nanoparticles were prepared by varying the molecular weights of polymer grafted from the nanoparticles (N) and polymer forming the matrix (P). We were able to associate a critical force for the onset of nanowear by analyzing the nanowear patterns resulting from different normal loads during the nanowear experiment. The definition of this critical force allows quantitative comparison of nanoparticle-polymer systems of different composition. Nanowear tests indicated that only mixtures where N/P> 1 reinforced the composite material compared to the pure homopolymer. Under these conditions the grafted polymers were swollen and the nanoparticles acted as additional anchor sites. As reference experiments we used a blend made from PEMA homopolymer and unmodified particles. Non-grafted nanoparticles clearly did not account for any reinforcement. © 2011 Elsevier B.V.
    view abstractdoi: 10.1016/j.wear.2011.05.040
  • 2011 • 40 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 abstractdoi: 10.1002/smll.201001734
  • 2011 • 39 Thermo-mechanical behaviour of Shape Memory Polymers, e.g., Tecoflex® by 1WE method: SEM and IR analysis
    Schmidt, C. and Chowdhury, A.M.S. and Neuking, K. and Eggeler, G.
    Journal of Polymer Research 18 1807-1812 (2011)
    Thermomechanical cycles including programming, cooling, unloading and heating to trigger the 1WE were examined for a shape memory polymer (SMP), Tecoflex® (TFX EG-72D). Cycles were performed at 60 °C with 65% strains and the recovery time of 10 min. Strains evolving with time were estimated during the thermomechanical treatments for the total 50 cycles using 65% strains. Recovery ratios for 65% strains were also estimated. It turns out that programming, cooling, unloading and heating to trigger the 1WE causes an increase of irreversible strain and is associated with a corresponding decrease of the intensity of the 1WE in particular during the first thermomechanical cycles. Gold coated scanning electron microscopic study using secondary electron imaging (120 times magnified) shows a very little wavy surface structure evolve during cycling up to 300% strains. IR study accurately features the chemical nature after cycling, processing and programming of TFX EG-72D. © 2011 Springer Science+Business Media B.V.
    view abstractdoi: 10.1007/s10965-011-9587-5
  • 2011 • 38 Mechanical behavior of shape memory polymers by 1we method: Application to tecoflex®
    Schmidt, C. and Chowdhury, A.M.S. and Neuking, K. and Eggeler, G.
    Journal of Thermoplastic Composite Materials 24 853-860 (2011)
    Thermomechanical cycles including programming, cooling, unloading, and heating to trigger the 1WE were examined for a shape memory polymer, Tecoflex® (TFX EG - 72D). Cycles were performed at 60°C with 300% strain and a recovery time of 10 min. Strains evolving with time were estimated during the thermomechanical treatments for the total 50 cycles using 300% strain. Recovery ratios for the 300% strain were also estimated. It turns out that programming, cooling, unloading and heating to trigger the 1WE causes an increase of irreversible strain and is associated with a corresponding decrease of the intensity of the 1WE in particular during the first thermomechanical cycles. © 2011 The Author(s).
    view abstractdoi: 10.1177/0892705711407785
  • 2011 • 37 Studies on the cycling, processing and programming of an industrially applicable shape memory polymer Tecoflex® (or TFX EG 72D)
    Schmidt, C. and Chowdhury, A.M.S. and Neuking, K. and Eggeler, G.
    High Performance Polymers 23 300-307 (2011)
    The present investigations were undertaken to find out whether and how often cycling, processing and programming can be repeated, whether repeated programming affects the one way effect and how much irreversible strain the shape memory polymeric material accumulates at a particular temperature. The effect was investigated in dependence of different stress levels, and the effect of both recovery temperature and recovery time was considered. As a model material the commercially and industrially applicable amorphous shape memory polymer Tecoflex® was examined and subjected to 50 programming cycles. Tecoflex® is characterized by a glass transition temperature, Tg, of 74 °C, above which it looses all its strength. During tensile testing at 20 °C (T < Tg), stresses a steady increase to 26 MPa as strains approached the rupture strain of 25%. It is observed that at 60 °C (T < Tg, but near Tg) the material can be strained to more than 2500% before rupture occurs while stresses slowly increase to values less than 0.3 MPa. It turns out that programming, cooling, unloading and heating to trigger the one way effect causes an increase of irreversible strain that is associated with a corresponding decrease of the intensity of the one way effect during the first thermomechanical cycles. © The Author(s) 2011.
    view abstractdoi: 10.1177/0954008311405245
  • 2011 • 36 Stress-strain behavior of shape memory polymers by 1 WE method: Application to tecoflex®
    Schmidt, C. and Chowdhury, A.M.S. and Neuking, K. and Eggeler, G.
    Journal of Macromolecular Science, Part A: Pure and Applied Chemistry 48 204-210 (2011)
    Thermomechanical cycles including programming, cooling, unloading and heating to trigger the 1WE were examined for a shape memory polymer (SMP), Tecoflex® (TFX EG-72D). Cycles were performed at 60°C with 50% and 225% strains and the recovery time of 10 min. Strains evolving with time were estimated during the thermomechanical treatments for the total 44 cycles using 50% strains and the total 50 cycles using 225% strains. Recovery ratios for 50% strains and 225% were also estimated. It turns out that programming, cooling, unloading and heating to trigger the 1WE causes an increase of irreversible strain and is associated with a corresponding decrease of the intensity of the 1WE in particular during the first thermomechanical cycles. In parallel scanning electron microscopic study using secondary electron imaging shows a very slight wavy surface structure evolved during cycling. Copyright © Taylor & Francis Group, LLC.
    view abstractdoi: 10.1080/10601325.2011.544630
  • 2011 • 35 Electron transfer between genetically modified Hansenula polymorpha yeast cells and electrode surfaces via os-complex modified redox polymers
    Shkil, H. and Schulte, A. and Guschin, D.A. and Schuhmann, W.
    ChemPhysChem 12 806-813 (2011)
    Graphite electrodes modified with redox-polymer-entrapped yeast cells were investigated with respect to possible electron-transfer pathways between cytosolic redox enzymes and the electrode surface. Either wild-type or genetically modified Hansenula polymorpha yeast cells over-expressing flavocytochrome b2 (FC b2) were integrated into Os-complex modified electrodeposition polymers. Upon increasing the L-lactate concentration, an increase in the current was only detected in the case of the genetically modified cells. The overexpression of FC b2 and the related amplification of the FC b2/L-lactate reaction cycle was found to be necessary to provide sufficient charge to the electron-exchange network in order to facilitate sufficient electrochemical coupling between the cells, via the redox polymer, to the electrode. The close contact of the Os-complex modified polymer to the cell wall appeared to be a prerequisite for electrically wiring the cytosolic FC b2/L-lactate redox activity and suggests the critical involvement of a plasma membrane redox system. Insights in the functioning of whole-cell-based bioelectrochemical systems have to be considered for the successful design of whole-cell biosensors or microbial biofuel cells. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cphc.201000889
  • 2011 • 34 Solid-phase temperature measurements in a HTPEM fuel cell
    Siegel, C. and Bandlamudi, G. and Heinzel, A.
    International Journal of Hydrogen Energy 36 12977-12990 (2011)
    Segmented temperature measurements were performed to better understand the thermal behaviour and thermal interactions between the fluid-(gas)-phase and solid-phase temperature within a working high temperature polymer electrolyte membrane (HTPEM) fuel cell. Three types of flow-fields were studied, and the influence of temperature for no-load and load operating conditions was investigated. Tests were performed under various operating conditions, and the results demonstrate the utility of segmented temperature measurements. A significant difference in the temperature distribution was observed when the HTPEM fuel cell was operated with pure hydrogen and with hydrogen containing carbon monoxide. The findings may lead to improved HTPEM fuel cells and future middle temperature polymer electrolyte membrane (MTPEM) fuel cell designs. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.ijhydene.2011.07.027
  • 2011 • 33 Systematic characterization of a PBI/H3PO4 sol-gel membrane - Modeling and simulation
    Siegel, C. and Bandlamudi, G. and Heinzel, A.
    Journal of Power Sources 196 2735-2749 (2011)
    This work presents a three-dimensional, steady-state, non-isothermal model of a high-temperature polymer-electrolyte-membrane fuel cell (HTPEMFC) using a phosphoric acid-doped polybenzimidazole (PBI/H3PO4) sol-gel membrane. The model accounts for the gold-plated copper current collector plates, the bipolar plates, all gas flow channels (flow-field), the gas diffusion layers, the reaction layers, and the membrane. Electrochemical reactions are modeled using an agglomerate approach and include the gas diffusivity and the gas solubility. The conductivity of the membrane is modeled using the Arrhenius equation to describe the temperature dependence. Finite elements are used to discretize all computational subdomains, and a commercially available code is used to solve the problem. The predicted values are compared to typical operating conditions, and a good agreement is found. The current density, the solid- and fluid-(gas)-phase temperatures and other quantities are analyzed throughout the computational subdomains. It was observed that the Arrhenius approach is valid in a certain temperature range and may overpredict the PBI/H3PO4 sol-gel membrane conductivity at higher solid-phase temperatures. Moreover, it is shown how the fluid-(gas)-phase temperature influences the solid-phase temperature and the current density distribution. Concrete values are deduced from the simulations and discussed according to experimental test. © 2010 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.jpowsour.2010.11.028
  • 2011 • 32 Amphiphilic polymer conetworks as chiral separation membranes
    Tobis, J. and Boch, L. and Thomann, Y. and Tiller, J.C.
    Journal of Membrane Science 372 219-227 (2011)
    There is an urgent need for enantiopure chemicals, e.g., as basic compounds for pharmaceuticals. Although great progress has been made to obtain these compound using chiral catalysts, enzymes or even whole cells, it is often not possible or at least not economic to obtain enantiopure compounds. Thus enantioseparation is still required. Besides the elaborate and expensive chromatography and crystallization techniques, chiral membranes have been found to be effective in enantioseparation. Generally such membranes have to be developed specifically for a certain compound in a suited solvent. This is an elaborate development, because little is known about the complex transport process through a chiral membrane. In order to get better insights in the function of such membranes, we have designed a new class of chiral separating membranes that are applicable for nearly every solvent and therefore potentially many substrates. The conetworks are based on nanophasic, amphiphilic polymer conetworks (APCN) featuring a chiral phase of poly((R),(S)- N-(1-hydroxy-butan-2-yl)acrylamide) (P-(R),(S)-HBA) and a non-chiral polydimethylsiloxane (PDMS) phase. This APCN allows to directly exploring interactions between a chiral membrane and an enantiopure compound in dependence on a broad range of solvents varying from n-heptane to water by simply measuring the permeabilities of the compounds. Besides the numerous insights in the solvent-dependent interactions between membrane and five model substrates, we demonstrate that the APCNs are excellent chiral separation membranes. Further, it could be shown that the superior selectivity of these materials is based on the structure of their nanophases. © 2011 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2011.02.004
  • 2011 • 31 Photoluminescent zinc oxide polymer nanocomposites fabricated using picosecond laser ablation in an organic solvent
    Wagener, P. and Faramarzi, S. and Schwenke, A. and Rosenfeld, R. and Barcikowski, S.
    Applied Surface Science 257 7231-7237 (2011)
    Nanocomposites made of ZnO nanoparticles dispersed in thermoplastic polyurethane were synthesized using picosecond laser ablation of zinc in a polymer-doped solution of tetrahydrofuran. The pre-added polymer stabilizes the ZnO nanoparticles in situ during laser ablation by forming a polymer shell around the nanoparticles. This close-contact polymer shell has a layer thickness up to 30 nm. Analysis of ZnO polyurethane nanocomposites using optical spectroscopy, high resolution transmission electron microscopy and X-ray diffraction revealed that oxidized and crystalline ZnO nanoparticles were produced. Those nanocomposites showed a green photoluminescence emission centred at 538 nm after excitation at 350 nm, which should be attributed to oxygen defects generated during the laser formation mechanism of the monocrystalline nanoparticles. Further, the influence of pulse energy and polymer concentration on the production rate, laser fluence and energy-specific mass productivity was investigated. © 2011 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2011.03.097
  • 2011 • 30 Impact of in situ polymer coating on particle dispersion into solid laser-generated nanocomposites
    Wagener, P. and Brandes, G. and Schwenke, A. and Barcikowski, S.
    Physical Chemistry Chemical Physics 13 5120-5126 (2011)
    The crucial step in the production of solid nanocomposites is the uniform embedding of nanoparticles into the polymer matrix, since the colloidal properties or specific physical properties are very sensitive to particle dispersion within the nanocomposite. Therefore, we studied a laser-based generation method of a nanocomposite which enables us to control the agglomeration of nanoparticles and to increase the single particle dispersion within polyurethane. For this purpose, we ablated targets of silver and copper inside a polymer-doped solution of tetrahydrofuran by a picosecond laser (using a pulse energy of 125 μJ at 33.3 kHz repetition rate) and hardened the resulting colloids into solid polymers. Electron microscopy of these nanocomposites revealed that primary particle size, agglomerate size and particle dispersion strongly depend on concentration of the polyurethane added before laser ablation. 0.3 wt% polyurethane is the optimal polymer concentration to produce nanocomposites with improved particle dispersion and adequate productivity. Lower polyurethane concentration results in agglomeration whereas higher concentration reduces the production rate significantly. The following evaporation step did not change the distribution of the nanocomposite inside the polyurethane matrix. Hence, the in situ coating of nanoparticles with polyurethane during laser ablation enables simple integration into the structural analogue polymer matrix without additives. Furthermore, it was possible to injection mold these in situ-stabilized nanocomposites without affecting particle dispersion. This clarifies that sufficient in situ stabilization during laser ablation in polymer solution is able to prevent agglomeration even in a hot polymer melt. © the Owner Societies 2011.
    view abstractdoi: 10.1039/c0cp02262d
  • 2011 • 29 High wear resistant deep drawing tools made of coated polymers
    Witulski, J. and Trompeter, M. and Tekkaya, A.E. and Kleiner, M.
    CIRP Annals - Manufacturing Technology 60 311-314 (2011)
    A methodology for the rapid production of drawing tools with high wear resistance to form free-form shaped sheet metal parts is developed. Hard material shells are thermally sprayed on an original mould and supported by a polymer. The bonded shell is removed from the original mould and acts as the surface of the forming tool. Deep drawing experiments show that the wear resistance of these hybrid tools is adequate to form high-strength steels. The tools are a suitable alternative to existing tool systems for the intended use in small up to medium size productions. © 2011 CIRP.
    view abstractdoi: 10.1016/j.cirp.2011.03.149
  • 2011 • 28 Peptide functionalized polydiacetylene liposomes Act as a fluorescent turn-on sensor for bacterial lipopolysaccharide
    Wu, J. and Zawistowski, A. and Ehrmann, M. and Yi, T. and Schmuck, C.
    Journal of the American Chemical Society 133 9720-9723 (2011)
    Mixed polydiacetylene (PDA) liposomes functionalized on their surface with a fluorescent pentalysine peptide derivative and histidine in a ratio of 1:9 can identify bacterial lipopolysaccharide (LPS). Upon photopolymerization of the self-assembled liposomes the initial fluorescence of the peptide-diacetylene amphiphiles is quenched. Interaction with LPS in aqueous solution or on the surface of E. coli DH5α restores the fluorescence. This increase in fluorescence is selective for LPS relative to other negatively charged analytes including nucleotides and ctDNA. This simple turn-on fluorescent sensor allows detecting LPS even at low micromolar concentrations. © 2011 American Chemical Society.
    view abstractdoi: 10.1021/ja204013u
  • 2011 • 27 Cylindrical membrane pores with well-defined grafted linear and comblike glycopolymer layers for lectin binding
    Yang, Q. and Ulbricht, M.
    Macromolecules 44 1303-1310 (2011)
    Glycopolymers with well-defined linear or comblike structure were grafted to poly(ethylene terephthalate) (PET) track-etched membrane surface by surface-initiated atom transfer radical polymerization (ATRP). Bromoalkyl initiator was directly immobilized onto PET membrane surface, and the ATRP of 2-lactobionamidoethyl methacrylate (LAMA) was then carried out to yield the grafted linear glycopolymer. Comblike poly(LAMA) was constructed on PET membrane by a two-step sequence. First, ATRP of 2-hydroxyethyl methacrylate (HEMA) was initiated from the PET surface, and alkyl bromide was then immobilized to poly(HEMA) chains. The initiator-immobilized poly(HEMA) served as a surface tethered macroinitiator for the ATRP of poly(LAMA) and resulted in comblike polyLAMA branches. The ATRP conditions for both LAMA and HEMA were optimized, and the thus-established grafting was well controlled. The dry layer thickness (DLT) of grafted polymers was deduced from results of capillary flow porometer measurements. Effective hydrodynamic layer thickness was estimated from pure water permeability. Data revealed that the grafted linear poly(LAMA) and poly(HEMA) had relatively low chain density and exhibited a collapsed coil conformation in dry state. After grafting of poly(LAMA) chains to poly(HEMA) this collapse was significantly hindered by the steric influence of poly(LAMA) branches on the poly(HEMA) main chains, and more than 3 times increase in DLT could be observed. Nonspecific protein binding, studied with bovine serum albumin, was very low for membranes with grafted linear poly(LAMA) while no adsorbed protein could be detected for the comblike poly(LAMA) architecture. Both membranes were then used for binding of peanut agglutinin, a lectin specifically binding to galactose. Under conditions where protein could only diffuse into the membrane pores, comblike poly(LAMA) showed only slight enhancement of binding capacity in comparison with the linear poly(LAMA). However, with convective flow through the membranes, binding capacity of the comblike poly(LAMA) layer was significantly increased and a capacity up to 23.6 mg/cm3 was achieved. Specific lectin binding with high capacities, corresponding to 3-dimensional protein stacking in the grafted layers, could be confirmed. © 2011 American Chemical Society.
    view abstractdoi: 10.1021/ma1025972
  • 2011 • 26 Liquid-phase epitaxy of multicomponent layer-based porous coordination polymer thin films of [M(L)(P)0.5] type: Importance of deposition sequence on the oriented growth
    Zacher, D. and Yusenko, K. and Bétard, A. and Henke, S. and Molon, M. and Ladnorg, T. and Shekhah, O. and Schüpbach, B. and Dea Losa Arcos, T. and Krasnopolski, M. and Meilikhov, M. and Winter, J. and Terfort, A. and Wöll, C. a...
    Chemistry - A European Journal 17 1448-1455 (2011)
    The progressive liquid-phase layer-by-layer (LbL) growth of anisotropic multicomponent layer-based porous coordination polymers (PCPs) of the general formula [M(L)(P)0.5] (M: Cu2+, Zn2+; L: dicarboxylate linker; P: dinitrogen pillar ligand) was investigated by using either pyridyl- or carboxyl-terminated self-assembled monolayers (SAMs) on gold substrates as templates. It was found that the deposition of smooth, highly crystalline, and oriented multilayer films of these PCPs depends on the conditions at the early growth cycles. In the case of a two-step process with an equimolar mixture of L and P, growth along the [001] direction is strongly preferred. However, employing a three-step scheme with full separation of all components allows deposition along the [100] direction on carboxyl-terminated SAMs. Interestingly, the growth of additional layers on top of previously grown oriented seeding layers proved to be insensitive to the particular growth scheme and full retention of the initial orientation, either along the [001] or [100] direction, was observed. This homo- and heteroepitaxial LbL growth allows full control over the orientation and the layer sequence, including introduction of functionalized linkers and pillars. One layer at a time: The stepwise liquid-phase layer-by-layer growth of anisotropic, multicomponent layer-based porous coordination polymers (PCPs) of the general formula [M(L)(P) 0.5] (M: Cu2+, Zn2+; L: dicarboxylate linker, P: dinitrogen pillar ligand) was investigated by using either pyridyl- or carboxyl-terminated self-assembled monolayers as templates. Highly oriented PCP multilayers were selectively grown along the [100] and [001] directions (see figure). © 2011 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/chem.201002381
  • 2010 • 25 Design of a bioelectrocatalytic electrode interface for oxygen reduction in biofuel cells based on a specifically adapted Os-complex containing redox polymer with entrapped Trametes hirsuta laccase
    Ackermann, Y. and Guschin, D.A. and Eckhard, K. and Shleev, S. and Schuhmann, W.
    Electrochemistry Communications 12 640-643 (2010)
    The design of the coordination shell of an Os-complex and its integration within an electrodeposition polymer enables fast electron transfer between an electrode and a polymer entrapped high-potential laccase from the basidiomycete Trametes hirsuta. The redox potential of the Os3+/2+-centre tethered to the polymer backbone (+ 720 mV vs. NHE) is perfectly matching the potential of the enzyme (+ 780 mV vs. NHE at pH 6.5). The laccase and the Os-complex modified anodic electrodeposition polymer were simultaneously precipitated on the surface of a glassy carbon electrode by means of a pH-shift to 2.5. The modified electrode was investigated with respect to biocatalytic O2 reduction to H2O. The proposed modified electrode has potential applications as biofuel cell cathode. © 2010 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.elecom.2010.02.019
  • 2010 • 24 Amphiphilic polymer conetworks as matrices for phase transfer reactions
    Bruns, N. and Hanko, M. and Dech, S. and Ladisch, R. and Tobis, J. and Tiller, J.C.
    Macromolecular Symposia 291-292 293-301 (2010)
    Amphiphilic polymer conetworks were prepared, characterized and used as highly activating matrices for phase transfer reactions. Several applications such as biocatalysis in organic solvents, metathesis reactions in water, biosensor designs for detecting metabolites in organic solvents, as well as gas sensor designs are discussed. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/masy.201050534
  • 2010 • 23 Trap states and space charge limited current in dispersion processed zinc oxide thin films
    Bubel, S. and Mechau, N. and Hahn, H. and Schmechel, R.
    Journal of Applied Physics 108 (2010)
    The electric transport properties of nanoparticulate zinc oxide (ZnO) thin films are investigated in nitrogen and ambient atmosphere with respect to the effects of polymer adsorbates, in order to study the origin of hysteresis behavior of ZnO thin film transistors. A strong dependence on the polymer adsorbate of the conductivity in nitrogen atmosphere is observed. Utilizing the space charge limited current theory, the trap depth and concentration in the films have been estimated. According to this analysis, the low conductivity of polymer free thin films in ambient atmosphere is caused by an increase in deep traps, compensating free charge carriers and not by a reduction in donorlike defect states. Furthermore, polymeric additives seem to induce similar trap states, which make the transport properties less sensitive against atmospheric influences. However, the strongly compensated semiconductor created in this way, causes a slow trap and release behavior resulting in a strong hysteresis in the transistor characteristics and long-term instabilities. It is shown, that ignoring these time-dependent characteristics, straight forward derived transistor parameters like the field effect mobility can be easily overestimated. © 2010 American Institute of Physics.
    view abstractdoi: 10.1063/1.3524184
  • 2010 • 22 Adhesion energies of Cr thin films on polyimide determined from buckling: Experiment and model
    Cordill, M.J. and Fischer, F.D. and Rammerstorfer, F.G. and Dehm, G.
    Acta Materialia 58 5520-5531 (2010)
    For the realization of flexible electronic devices, the metal-polymer interfaces upon which they are based need to be optimized. These interfaces are prone to fracture in such systems and hence form a weak point. In order to quantify the interfacial adhesion, novel mechanical tests and modeling approaches are required. In this study, a tensile testing approach that induces buckling of films by lateral contraction of the substrate is employed to cause delamination of the film. Based on a newly developed energy balance model, the adhesion energy of Cr films on polyimide substrates is determined by measuring the buckle geometry induced by the tensile test. The obtained minimum values for the adhesion energy (about 4.5 J m-2) of 50-190 nm thick films compare well to those found in the literature for metal films on polymer substrates. © 2010 Acta Materialia Inc. Published by Elsevier Ltd.
    view abstractdoi: 10.1016/j.actamat.2010.06.032
  • 2010 • 21 Fracture and delamination of chromium thin films on polymer substrates
    Cordill, M.J. and Taylor, A. and Schalko, J. and Dehm, G.
    Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science 41 870-875 (2010)
    New emerging technologies in the field of flexible electronic devices require that metal films adhere well and flex with polymer substrates. Common thin film materials used for these applications include copper (Cu) with an adhesion interlayer of chromium (Cr). Copper can be quite ductile and easily move with the polymer substrate. However, Cr is more brittle and fractures at lower strains than Cu. This study aims to examine the fracture and subsequent buckling and delamination of strained Cr films on polyimide (PI). In-situ scanning electron microscope (SEM) straining is used to systematically study the influence of film thickness on fracture and buckling strains. Film fracture and delamination depend on film thickness, and increases in crack and buckle density with decreasing thickness are explored by a shear lag model. © 2009 The Minerals, Metals & Materials Society and ASM International.
    view abstractdoi: 10.1007/s11661-009-9988-9
  • 2010 • 20 γ-Fe2O3 nanoparticle adsorption at an OTS Langmuir monolayer
    Degen, P. and Paulus, M. and Leick, S. and Tolan, M. and Rehage, H.
    Colloid and Polymer Science 288 643-651 (2010)
    The assembling of magnetic nanoparticles in ordered structures as well as the preparation of very thin magnetic switchable polymer membranes is an important aim in many technical fields. We studied the influence of γ-Fe2O3 nanoparticles on the polymerization process and on the properties of the poly(organosiloxane)/nanoparticle-composite layer by surface rheological measurements, surface pressure/area (π/A) isotherm measurements, and Brewster angle microscopy. The adsorption process dynamics were studied by X-ray reflectivity and surface potential measurements. The results confirm the presence of attractive electrostatic interactions between the partial negatively charged monolayer and the positively charged nanoparticles. For further investigations, we prepared Langmuir-Blodgett layers of these polymer-nanoparticle composite and investigated them by atomic force microscopy and UV-Vis spectroscopy. We found that the concentration of nanoparticles was very low and the particles were mainly arranged below the polymer layer. © 2010 Springer-Verlag.
    view abstractdoi: 10.1007/s00396-010-2191-0
  • 2010 • 19 Softlithographic, partial integration of surface-active nanoparticles in a PDMS matrix for microfluidic biodevices
    Demming, S. and Hahn, A. and Edlich, A. and Franco-Lara, E. and Krull, R. and Barcikowski, S. and Büttgenbach, S.
    Physica Status Solidi (A) Applications and Materials Science 207 898-903 (2010)
    The mergence of microfluidics and nanocomposite materials and their in situ structuring leads to a higher integration level within microsystems technology. Nanoparticles (Cu and Ag) produced via laser radiation were suspended in Poly(dimethylsiloxane) to permanently modify surface material. A microstructuring process was implemented which allows the incorporation of these nanomaterials globally or partially at defined locations within a microbioreactor (MBR) for the determination of their antiseptic and toxic effects on the growth of biomass. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/pssa.200983311
  • 2010 • 18 The effects of (macro)molecular structure on hydrophilic surface modification of polypropylene membranes via entrapment
    Guo, H. and Ulbricht, M.
    Journal of Colloid and Interface Science 350 99-109 (2010)
    Entrapment of a variety of ethyleneoxide-containing substances from nonpolar solutions into polypropylene (PP) microfiltration membrane surface for hydrophilic modification was studied. The results from gravimetric weight gain, surface characterization by contact angle measurements and ATR-IR spectroscopy, water flux measurements and protein adsorption revealed that poly(ethylene glycol)s (PEGs) were ineffective, while many nonionic amphiphilic substances, especially some tri-block copolymers of poly(ethyleneoxide) (PEO) and poly(propylene oxide) (PPO) were very effective for PP surface modification. The relationship between modifier structure and architecture and entrapment behavior was investigated by studying the micellization of the amphiphilic modifiers in nonpolar solutions via pyrene-probe fluorescence and 1H NMR spectroscopy. We observed that the balanced structure of nonionic tri-block (macro)molecules tended to promote the formation of reverse micelles. For the most efficient polymeric modifiers, the lowest reverse critical micelle concentration (RCMC) had been observed. We conclude that a block copolymer structure and architecture promoting the self-association in the nonpolar solvent is the basis for a high modification efficiency, and that reverse micelles are involved in the entrapment modification performed at concentrations above RCMC. A different mechanism has been deduced for amphiphilic modifiers with low molar mass. This work provides more comprehensive insights in surface entrapment as a easy to perform physical surface modification method for polymeric materials. © 2010 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcis.2010.06.032
  • 2010 • 17 Redox electrodeposition polymers: Adaptation of the redox potential of polymer-bound Os complexes for bioanalytical applications
    Guschin, D.A. and Castillo, J. and Dimcheva, N. and Schuhmann, W.
    Analytical and Bioanalytical Chemistry 398 1661-1673 (2010)
    The design of polymers carrying suitable ligands for coordinating Os complexes in ligand exchange reactions against labile chloro ligands is a strategy for the synthesis of redox polymers with bound Os centers which exhibit a wide variation in their redox potential. This strategy is applied to polymers with an additional variation of the properties of the polymer backbone with respect to pH-dependent solubility, monomer composition, hydrophilicity etc. A library of Os-complex-modified electrodeposition polymers was synthesized and initially tested with respect to their electron-transfer ability in combination with enzymes such as glucose oxidase, cellobiose dehydrogenase, and PQQ-dependent glucose dehydrogenase entrapped during the pH-induced deposition process. The different polymer-bound Os complexes in a library containing 50 different redox polymers allowed the statistical evaluation of the impact of an individual ligand to the overall redox potential of an Os complex. Using a simple linear regression algorithm prediction of the redox potential of Os complexes becomes feasible. Thus, a redox polymer can now be designed to optimally interact in electron-transfer reactions with a selected enzyme. © 2010 Springer-Verlag.
    view abstractdoi: 10.1007/s00216-010-3982-3
  • 2010 • 16 Framework for deformation induced anisotropy in glassy polymers
    Harrysson, M. and Ristinmaa, M. and Wallin, M. and Menzel, A.
    Acta Mechanica 211 195-213 (2010)
    In this paper a constitutive model for glassy polymers is developed. Glassy polymers consist of a number of polymer chains that at a microscopic level form a network. If the distribution of the polymer chains shows some preferred direction, the mechanical response at a global macroscopic level will be anisotropic. To incorporate the orientational distribution of the polymer chains, a homogenization procedure involving a chain orientation distribution function was undertaken. When polymers are exposed to external loading, the chains at the microscopic level orient in a certain manner, leading to an evolution of the macroscopic anisotropic properties. This phenomenon was modeled by use of evolution equations for the chains at a microscopic level and are then-by using the orientation distribution function-transformed to the macroscopic level. The theories involved are developed in a large strain setting in which a multiplicative split of the deformation gradient for the elastic-viscoplastic response is adopted. Various numerical experiments were conducted to evaluate the model that was developed. © 2009 Springer-Verlag.
    view abstractdoi: 10.1007/s00707-009-0232-x
  • 2010 • 15 Flexibility and Sorption Selectivity in Rigid Metal-Organic Frameworks: The Impact of Ether-Functionalised Linkers
    Henke, S. and Schmid, R. and Grunwaldt, J. D. and Fischer, R. A.
    Chemistry-a European Journal 16 14296--14306 (2010)
    The functionalisation of well-known rigid metal organic frameworks (namely, [Zn4O(bdc)(3)](n), MOF-5, IRMOF-1 and [Zn-2(bdc)(2)(dabco)](n); bdc = 1,4-benzene dicarboxylate, dabco=diazabicyclo[2.2.2]octane) with additional alkyl ether groups of the type -O-(CH2)(n)-O-CH3 (n = 2-4) initiates unexpected structural flexibility, as well as high sorption selectivity towards CO2 over N-2 and CH, in the porous materials. These novel materials respond to the presence/absence of guest molecules with structural transformations. We found that the chain length of the alkyl ether groups and the substitution pattern of the bdc-type linker have a major impact on structural flexibility and sorption selectivity. Remarkably, our results show that a high crystalline order of the activated material is not a prerequisite to achieve significant porosity and high sorption selectivity.
    view abstractdoi: 10.1002/chem.201002341
  • 2010 • 14 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 abstractdoi: 10.1021/la101014g
  • 2010 • 13 A Physicist's Perspective on "Views on Macroscopic Kinetics of Plasma Polymerisation"
    von Keudell, A. and Benedikt, J.
    Plasma Processes and Polymers 7 376--379 (2010)
    doi: 10.1002/ppap.201000011
  • 2010 • 12 Modelling semiflexible polymers: Shape analysis, buckling instabilities, and force generation
    Kierfeld, J. and Baczynski, K. and Gutjahr, P. and Kühne, T. and Lipowsky, R.
    Soft Matter 6 5764-5769 (2010)
    The behavior of semiflexible polymers and filaments is governed by their bending energy. The corresponding bending rigidity gives rise to material properties that are distinct from those of flexible polymers governed by entropy. In particular, bending rigidity plays an important role for the shapes of these polymers and their ability to withstand and transmit forces. Recent theoretical studies and modelling approaches are briefly reviewed and used for a systematic analysis of shapes of adsorbed semiflexible polymers and buckling instabilities. Semiflexible polymers and filaments exhibit a buckling instability which is modified by thermal fluctuations and provides upper bounds on the generation of polymerization forces. Growing bundles of polymers or filaments can generate force via adhesive interactions. The latter mechanism remains effective even after single filaments have attained a buckled state. © 2010 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c002035b
  • 2010 • 11 Positively charged calcium phosphate/polymer nanoparticles for photodynamic therapy
    Klesing, J. and Wiehe, A. and Gitter, B. and Gräfe, S. and Epple, M.
    Journal of Materials Science: Materials in Medicine 21 887-892 (2010)
    The charge of nanoparticles influences their ability to pass through the cellular membrane, and a positive charge should be beneficial. The negative charge of calcium phosphate nanoparticles with an inner shell of carboxymethyl cellulose (CMC) was reversed by adding an outer shell of poly(ethyleneimine) (PEI) into which the photoactive dye 5,10,15,20-tetrakis(3-hydroxyphenyl)- porphyrin (mTHPP) was loaded. The aqueous dispersion of the nanoparticles was used for photodynamic therapy with HT29 cells (human colon adenocarcinoma cells), HIG-82 cells (rabbit synoviocytes), and J774A.1 cells (murine macrophages). A high photodynamic activity (killing) together with a very low dark toxicity was observed for HIG-82 and for J774.1 cells at 2 μM dye concentration. The killing efficiency was equivalent to the pure photoactive dye that, however, needs to be administered in alcoholic solution. © 2009 Springer Science+Business Media, LLC.
    view abstractdoi: 10.1007/s10856-009-3934-7
  • 2010 • 10 Narrowly size distributed zinc-containing poly(acrylamide) latexes via inverse miniemulsion polymerization
    Kobitskaya, E. and Ekinci, D. and Manzke, A. and Plettl, A. and Wiedwald, U. and Ziemann, P. and Biskupek, J. and Kaiser, U. and Ziener, U. and Landfester, K.
    Macromolecules 43 3294-3305 (2010)
    Polyacrylamide nanoparticles containing zinc nitrate were prepared via inverse miniemulsion polymerization using ultrasound emulsification. The effects of sonication time, mode of sonication, nature and type of emulsifier, amount of zinc salt, solvent in the dispersed phase, nature of dispersed and continuous phases, and type of initiator on the nucleation mechanism, conversion, molecular mass of polymer, and size distribution of the latex particles were investigated. The results showed that an increase in sonication time up to 4 min and using an amphiphilic polymeric surfactant with a relatively short hydrophilic part improved both the monodispersity and the stability of the zinc-containing latexes. An increase in viscosity of the continuous phase (changed by means of different nonpolar solvents) and decrease in viscosity of the dispersed phase (varied by the amount of water) had also a positive effect on the monodispersity. At the same time, the average diameter of the particles in the range of 225 nm changed only marginally. The use of either highly hydrophilic (ammonium persulfate) or highly hydrophobic (2,2′-azobis(2- methylbutyronitrile)) initiators, and the transfer from miniemulsion polymerization to dispersion, precipitation, or a combination of several polymerization types by the modification of the dispersed and continuous medium spread the polydispersity of the latex particles and impaired the stability. Samples with small content of salt were used for unconventional nanolithography by subjecting a highly ordered layer of the nanoparticles to a plasma etching process. Highly ordered arrays of particles containing ZnO nanocrystals were observed. © 2010 American Chemical Society.
    view abstractdoi: 10.1021/ma902553a
  • 2010 • 9 Easy synthesis of hollow polymer, carbon, and graphitized microspheres
    Lu, A.-H. and Li, W.-C. and Hao, G.-P. and Spliethoff, B. and Bongard, H.-J. and Schaack, B.B. and Schüth, F.
    Angewandte Chemie - International Edition 49 1615-1618 (2010)
    "Chemical Equation Presented" Balls galorel A new approach was developed for the easy synthesis of hollow microspheres with amorphous or graphitized microstructure. Starting from one type of solid polymer sphere, a simple water washing treatment led to the formation of hollow structures. Diverse products such as hollow carbon or graphitized spheres can be obtained, depending on subsequent treatment methods (see picture). © 2010 Wlley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/anie.200906445
  • 2010 • 8 Tensile creep measurements of glassy VOC-loaded polymers
    Mueller, F. and Heuwers, B. and Katzenberg, F. and Tiller, J.C. and Sadowski, G.
    Macromolecules 43 8997-9003 (2010)
    The paper describes a new apparatus to measure tensile creep curves of polymer/volatile organic compound (VOC) systems, especially designed for measurements of small VOC loadings in glassy polymers. For the first time creep curves for glassy polymer/VOC systems are recorded. The measurements were performed for the system polystyrene/toluene at different toluene loads up to wtoluene = 0.13 and at temperatures of 30, 50, and 70 °C. It was found that increasing VOC mass fractions qualitatively influence the mechanical properties of a polymer in the same way like increasing temperature does. Since at isothermal conditions these properties are affected by the glass transition of the system, this information for the polystyrene/toluene mixtures was used to modify and to verify the correlation of Kelly and Bueche to predict the glass-transition temperature of polymer/solvent systems. © 2010 American Chemical Society.
    view abstractdoi: 10.1021/ma101782d
  • 2010 • 7 Development of molecular and solid catalysts for the direct low-temperature oxidation of methane to methanol
    Palkovits, R. and von Malotki, C. and Baumgarten, M. and Müllen, K. and Baltes, C. and Antonietti, M. and Kuhn, P. and Weber, J. and Thomas, A. and Schüth, F.
    ChemSusChem 3 277-282 (2010)
    The direct low-temperature oxidation of methane to methanol is demonstrated on a highly active homogeneous molecular catalyst system and on heterogeneous molecular catalysts based on polymeric materials possessing ligand motifs within the material structure. The N-(2-methylpropyl)-4,5-diazacarbazolyl-dichloro-platinum(II) complex reaches significantly higher activity compared to the well-known Periana system and allows first conclusions on electronic and structural requirements for high catalytic activity in this reaction. Interestingly, comparable activities could be achieved utilizing a platinum modified poly(benzimidazole) material, which demonstrates for the first time a solid catalyst with superior activity compared to the Periana system. Although the material shows platinum leaching, improved activity and altered electronic properties, compared to the conventional Periana system, support the proposed conclusions on structure-activity relationships. In comparison, platinum modified triazine-based catalysts show lower catalytic activity, but rather stable platinum coordination even after several catalytic cycles. Based on these systems, further development of improved solid catalysts for the direct low-temperature oxidation of methane to methanol is feasible. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cssc.200900123
  • 2010 • 6 A sol-gel based surface treatment for preparation of water repellent antistatic textiles
    Textor, T. and Mahltig, B.
    Applied Surface Science 256 1668-1674 (2010)
    In this paper a surface treatment is described for preparation of hydrophobic sol-gel coatings that simultaneously offer antistatic properties for an appropriate finishing of textiles and refinement of polymer foils. Sol-gel based formulations are modified with both hydrophilic and hydrophobic components simultaneously. Hydrophobic components are, e.g., alkoxysilanes modified with alkyl chains while the hydrophilic ones are amino-functionalized alkoxysilanes. The basic idea is that due to an enrichment of hydrophobic groups at the solid/air interface the surface of the as prepared coatings will be hydrophobic while the deeper region will be more hydrophilic. Textiles finished with these coatings exhibit sufficient water repellence and simultaneously absorb sufficient amounts of humidity in the deeper areas of the coating guaranteeing antistatic properties. This concept offers interesting approaches for the preparation of multifunctional surface coatings not only focussing on combining water repellence with antistatic properties for textile materials. © 2009 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.apsusc.2009.09.091
  • 2010 • 5 Toward process optimization in laser welding of metal to polymer
    Tillmann, W. and Elrefaey, A. and Wojarski, L.
    Materialwissenschaft und Werkstofftechnik 41 879-883 (2010)
    The joining technology of dissimilar lightweight materials between metals and polymer is essential for realizing cars with hybrid structures and for other engineering applications. These types of joints are still difficult to generate and their behaviour is not fully understood. Laser welding offers specific process advantages over conventional technologies, such as short process times, while providing optically and qualitatively valuable weld seams and imposing minimal thermal stress. Furthermore, the process is compatible with automation. This paper summarizes the efforts to attain suitable joint strengths with the stainless steel plate type S30400 and a Polyethylene Terephtalate Glycol (PETG) plastic sheet. The study considers the optimization of two important process parameters, namely laser power, and welding speed. Microstructure features, test of tensile shear strength, investigation of the fracture location, and morphology were used to evaluate the joint performance. The result indicates that there is an optimum value for laser power, which achieves a sufficient melting and heat transfer to the joint without decomposing the plastic sheet and hence, enables to obtain high joint strength. Moreover, a low welding speed is preferable in most combinations of welding parameters since it achieves an adequate melting and wetting of the polymer to the steel surface. Copyright 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/mawe.201000674
  • 2010 • 4 Synthesis and characterization of chiral and thermo responsive amphiphilic conetworks
    Tobis, J. and Thomann, Y. and Tiller, J.C.
    Polymer 51 35-45 (2010)
    Amphiphilic polymer conetworks (APCN) combine the properties of different polymers on the nanoscale affording advanced materials with unique properties. Here, we present the first APCN with a chiral hydrophilic phase. The conetworks were prepared by copolymerizing the tailored chiral monomer (R)-N-(1-hydroxybutan-2-yl)acrylamide (R-HBA) with two different crosslinkers that consist of bitelechelic methacrylate-terminated poly(dimethylsiloxane) (PDMS) of a molecular weight of 1100 g/mol and 5620 g/mol, respectively. The resulting polymer conetworks P-R-HBA-l-PDMS exhibited both two different Tg values, indicating nanophase separation. However, the conetwork with PDMS1.1 did not show nanophases in the AFM and did not swell the phases separately in orthogonal solvents. On the other hand the materials with PDMS5.6 acted like a typical APCN. The APCN P-R-HBA-l-PDMS5.6 was found to be temperature sensitive in water, decreasing its degree of swelling linearly with increasing temperature. Additionally, the conetwork is increasing its degree of swelling in n-heptane in the region of the Tg of the P-R-HBA phase. The impact of the chiral polymer on the release of cinchona alkaloids was examined. For example, (-)-cinchonine diffuses four times faster off the P-R-HBA-l-PDMS networks than off the P-S-HBA-l-PDMS conetworks. © 2009 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.polymer.2009.10.055
  • 2010 • 3 A new family of nonionic dendritic amphiphiles displaying unexpected packing parameters in micellar assemblies
    Trappmann, B. and Ludwig, K. and Radowski, M.R. and Shukla, A. and Mohr, A. and Rehage, H. and Böttcher, C. and Haag, R.
    Journal of the American Chemical Society 132 11119-11124 (2010)
    In this paper we report on the synthesis of a new family of nonionic dendritic amphiphiles that self-assemble into defined supramolecular aggregates. Our approach is based on a modular architecture consisting of different generations of hydrophilic polyglycerol dendrons [G1-G3] connected to hydrophobic C11 or C16 alkyl chains via mono- or biaromatic spacers, respectively. All amphiphiles complex hydrophobic compounds as demonstrated by solubilization of Nile Red or pyrene. The structure of the supramolecular assemblies as well as the aggregation numbers are strongly influenced by the type of the dendritic headgroup. While the [G1] amphiphiles form different structures such as ringlike and fiberlike micelles, the [G2] and [G3] derivatives aggregate toward spherical micelles of low polydispersity clearly proven by transmission electron microscopy (TEM) measurements. In the case of the biaromatic [G2] derivative, the structural persistence of the micelles allowed a three-dimensional structure determination from the TEM data and confirmed the aggregation number obtained by static light scattering (SLS) measurements. On the basis of these data, molecular packing geometries indicate a drastic mass deficit of alkyl chains in the hydrophobic core volume of spherical micelles. It is noteworthy that these highly defined micelles contain as little as 15 molecules and possess up to 74% empty space. This behavior is unexpected as it is very different from classical detergent micelles such as sodium dodecyl sulfate (SDS), where the hydrophobic core volume is completely filled by alkyl chains. © 2010 American Chemical Society.
    view abstractdoi: 10.1021/ja101523v
  • 2010 • 2 Laser fragmentation of organic microparticles into colloidal nanoparticles in a free liquid jet
    Wagener, P. and Barcikowski, S.
    Applied Physics A: Materials Science and Processing 101 435-439 (2010)
    We present a novel approach for laser fragmentation of melamine cyanurate microcrystals suspended in liquid into colloidal nanoparticles. Laser fragmentation is done by irradiating a liquid jet of melamine cyanurate suspended in water with intense picosecond pulses. The free liquid jet is generated by a nozzle with small diameter and provides a thin liquid filament (d fil< 1 mm) perpendicular to the focused laser beam. This geometry allows tight focusing resulting in high intensities without the danger of damaging an optical element like windows necessary in conventional flow cells or cuvettes. It reduces losses of excitation light by avoiding scattering or absorption in front of the focus. We stabilized the nanoparticles electrosterically in-situ with neutral and polyelectrolytic polymers preventing agglomeration and precipitation. The threshold for sufficient stabilization of laser-fragmented nanoparticles (d hydrodyn≈200 nm) is reached at a mass fraction of 0.25 wt% dextrin as a neutral polymer and 0.01 wt% polyacrylic acid as a polyelectrolytic polymer. Hydrodynamic size and zeta-potential of the nanoparticles can be controlled by mass fraction of the stabilization agent. © 2010 The Author(s).
    view abstractdoi: 10.1007/s00339-010-5814-x
  • 2010 • 1 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 abstractdoi: 10.1021/la903895q