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- ItemFe3O4 Nanoparticles Grown on Cellulose/GO Hydrogels as Advanced Catalytic Materials for the Heterogeneous Fenton-like Reaction(Washington, DC : ACS Publications, 2019) Chen, Yian; Pötschke, Petra; Pionteck, Jürgen; Voit, Brigitte; Qi, HaisongCellulose/graphene oxide (GO)/iron oxide (Fe3O4) composites were prepared by coprecipitating iron salts onto cellulose/GO hydrogels in a basic solution. X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared, and X-ray diffraction characterization showed that Fe3O4 was successfully coated on GO sheets and cellulose. Cellulose/GO/Fe3O4 composites showed excellent catalytic activity by maintaining almost 98% of the removal of acid orange 7 (AO7) and showed stability over 20 consecutive cycles. This performance is attributable to the synergistic effect of Fe3O4 and GO during the heterogeneous Fenton-like reaction. Especially, the cellulose/GO/Fe3O4 composites preserve their activity by keeping the ratio of Fe3+/Fe2+ at 2 even after 20 catalysis cycles, which is supported by XPS analysis.
- ItemLightweight polymer-carbon composite current collector for lithium-ion batteries(Basel : MDPI, 2020) Fritsch, Marco; Coeler, Matthias; Kunz, Karina; Krause, Beate; Marcinkowski, Peter; Pötschke, Petra; Wolter, Mareike; Michaelis, AlexanderA hermetic dense polymer-carbon composite-based current collector foil (PCCF) for lithium-ion battery applications was developed and evaluated in comparison to state-of-the-art aluminum (Al) foil collector. Water-processed LiNi0.5Mn1.5O4 (LMNO) cathode and Li4Ti5O12 (LTO) anode coatings with the integration of a thin carbon primer at the interface to the collector were prepared. Despite the fact that the laboratory manufactured PCCF shows a much higher film thickness of 55 µm compared to Al foil of 19 µm, the electrode resistance was measured to be by a factor of 5 lower compared to the Al collector, which was attributed to the low contact resistance between PCCF, carbon primer and electrode microstructure. The PCCF-C-primer collector shows a sufficient voltage stability up to 5 V vs. Li/Li+ and a negligible Li-intercalation loss into the carbon primer. Electrochemical cell tests demonstrate the applicability of the developed PCCF for LMNO and LTO electrodes, with no disadvantage compared to state-of-the-art Al collector. Due to a 50% lower material density, the lightweight and hermetic dense PCCF polymer collector offers the possibility to significantly decrease the mass loading of the collector in battery cells, which can be of special interest for bipolar battery architectures. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
- ItemInfluence of a supplemental filler in twin-screw extruded PP/CNT composites using masterbatch dilution(Melville, NY : AIP, 2019) Müller, Michael Thomas; Krause, Beate; Kretzschmar, Bernd; Pötschke, PetraIn this study commercially available multiwalled carbon nanotubes (2-8 wt.%) were incorporated in polypropylene (PP) by direct powder feeding or by a masterbatch dilution procedure using a twin-screw extruder. The influence of a supplemental, electrical non-conductive talc or electrically conductive carbon black (CB), filler on the resulting composite properties was investigated. In comparison to the direct carbon nanotube (CNT) incorporation the masterbatch dilution step resulted in improved CNT macro dispersion. The use of the supplemental fillers CB or talc does not show a significant influence on the CNT dispersion state. When compared to direct CNT incorporation, the second compounding process involved in masterbatch dilution leads to higher electrical resistivity of injection molded samples. On the other hand, the supplemental fillers talc or CB decreased the electrical resistivity values. With the addition of talc or CB an increase of the Young’s modulus due to the reinforcing effect of the second filler was achieved. However, no synergistic effect between the used supplemental fillers and the CNT on the mechanical properties was obtained.
- ItemHigh-Performance, Lightweight, and Flexible Thermoplastic Polyurethane Nanocomposites with Zn2+-Substituted CoFe2O4 Nanoparticles and Reduced Graphene Oxide as Shielding Materials against Electromagnetic Pollution(Washington, DC : ACS Publications, 2021-10-11) Anju; Yadav, Raghvendra Singh; Pötschke, Petra; Pionteck, Jürgen; Krause, Beate; Kuřitka, Ivo; Vilcakova, Jarmila; Skoda, David; Urbánek, Pavel; Machovsky, Michal; Masař, Milan; Urbánek, Michal; Jurca, Marek; Kalina, Lukas; Havlica, JaromirThe development of flexible, lightweight, and thin high-performance electromagnetic interference shielding materials is urgently needed for the protection of humans, the environment, and electronic devices against electromagnetic radiation. To achieve this, the spinel ferrite nanoparticles CoFe2O4 (CZ1), Co0.67Zn0.33Fe2O4 (CZ2), and Co0.33Zn0.67Fe2O4 (CZ3) were prepared by the sonochemical synthesis method. Further, these prepared spinel ferrite nanoparticles and reduced graphene oxide (rGO) were embedded in a thermoplastic polyurethane (TPU) matrix. The maximum electromagnetic interference (EMI) total shielding effectiveness (SET) values in the frequency range 8.2-12.4 GHz of these nanocomposites with a thickness of only 0.8 mm were 48.3, 61.8, and 67.8 dB for CZ1-rGO-TPU, CZ2-rGO-TPU, and CZ3-rGO-TPU, respectively. The high-performance electromagnetic interference shielding characteristics of the CZ3-rGO-TPU nanocomposite stem from dipole and interfacial polarization, conduction loss, multiple scattering, eddy current effect, natural resonance, high attenuation constant, and impedance matching. The optimized CZ3-rGO-TPU nanocomposite can be a potential candidate as a lightweight, flexible, thin, and high-performance electromagnetic interference shielding material.
- ItemThermal annealing to influence the vapor sensing behavior of co-continuous poly(lactic acid)/polystyrene/multiwalled carbon nanotube composites(Amsterdam [u.a.] : Elsevier Science, 2020) Li, Yilong; Pionteck, Jürgen; Pötschke, Petra; Voit, BrigitteWith the main purpose of being used as vapor leakage detector, the volatile organic compound (VOC) vapor sensing properties of conductive polymer blend composites were studied. Poly(lactic acid)/polystyrene/multi-walled carbon nanotube (PLA/PS/MWCNT) based conductive polymer composites (CPCs) in which the polymer components exhibit different interactions with the vapors, were prepared by melt mixing. CPCs with a blend composition of 50/50 wt% resulted in the finest co-continuous structure and selective MWCNT localization in PLA. Therefore, these composites were selected for sensor tests. Thermal annealing was applied aiming to maintain the blend structure but improving the sensing reversibility of CPC sensors towards high vapor concentrations. Different sensing protocols were applied using acetone (good solvent for PS and PLA) and cyclohexane (good solvent for PS but poor solvent for PLA) vapors. Increasing acetone vapor concentration resulted in increased relative resistance change (Rrel) of CPCs. Saturated cyclohexane vapor resulted in lower response than nearly saturated acetone vapor. The thermal annealing at 150 °C did not change the blend morphology but increased the PLA crystallinity, making the CPC sensors more resistant to vapor stimulation, resulting in lower Rrel but better reversibility after vapor exposure.
- ItemOrganic vapor sensing behavior of polycarbonate/polystyrene/multi-walled carbon nanotube blend composites with different microstructures(Amsterdam [u.a.] : Elsevier Science, 2019) Li, Yilong; Pionteck, Jürgen; Pötschke, Petra; Voit, BrigitteWith the focus on the use as leakage detectors, the vapor sensing behavior of conductive polymer composites (CPCs) based on polycarbonate/polystyrene/multi-walled carbon nanotube (PC/PS/MWCNT) blends with different blend ratios was studied as well as their morphological and electrical properties. In the melt mixed blend composites, the MWCNTs are preferentially localized in PC. At the PC/PS ratio of 70/30 wt%, the composites showed a sea-island structure, while for blends containing 40 wt% or 50 wt% PS co-continuous structures were developed resulting in a reduction in the MWCNT percolation threshold. The saturated vapors of the selected solvents have good interactions to PS but different interactions to PC. At 0.75 wt% MWCNT, sea-island CPCs showed high relative resistance change (Rrel) but poor reversibility towards moderate vapors like ethyl acetate and toluene, while CPCs with co-continuous structure exhibited lower Rrel and better reversibility. All CPCs showed poor reversibility towards vapor of the good solvent dichloromethane due to strong interactions between polymers and vapor. In the vapor of the poor solvent cyclohexane, CPCs with higher PS content showed increased Rrel. After extraction of the PS component by cyclohexane, the sensing response was decreased and the Rrel of the co-continuous blend even reached negative values.
- ItemMWCNT induced negative real permittivity in a copolyester of Bisphenol-A with terephthalic and isophthalic acids(Bristol : IOP Publ., 2020) Özdemir, Zeynep Güven; Daşdan, Dolunay Şakar; Kavak, Pelin; Pionteck, Jürgen; Pötschke, Petra; Voit, Brigitte; SüngüMısırlıoğlu, BanuIn the present study, the negative real permittivity behavior of a copolyester of bisphenol-A with terephthalic acid and isophthalic acid (PAr) containing 1.5 to 7.5 wt% multi-walled carbon nanotubes (MWCNTs) have been investigated in detail. The structural and morphological analysis of the melt-mixed composites was performed by Fourier transform infrared spectroscopy using attenuated total reflection (FTIR-ATR), atomic force microscopy (AFM), X-ray diffraction (XRD), and light microscopy. The influences of the MWCNT filler on the AC impedance, complex permittivity, and AC conductivity of the PAr polymer matrix were investigated at different operating temperatures varied between 296 K and 373 K. The transition from a negative to positive real permittivity was observed at different crossover frequencies depending on the MWCNT content of the composites whereas pure PAr showed positive values at all frequencies. The negative real permittivity characteristic of the composites was discussed in the context of Drude model. © 2020 The Author(s). Published by IOP Publishing Ltd.
- ItemThe Localization Behavior of Different CNTs in PC/SAN Blends Containing a Reactive Component(Basel : MDPI, 2021-3-1) Gültner, Marén; Boldt, Regine; Formanek, Petr; Fischer, Dieter; Simon, Frank; Pötschke, PetraCo-continuous blend systems of polycarbonate (PC), poly(styrene-co-acrylonitrile) (SAN), commercial non-functionalized multi-walled carbon nanotubes (MWCNTs) or various types of commercial and laboratory functionalized single-walled carbon nanotubes (SWCNTs), and a reactive component (RC, N-phenylmaleimide styrene maleic anhydride copolymer) were melt compounded in one step in a microcompounder. The blend system is immiscible, while the RC is miscible with SAN and contains maleic anhydride groups that have the potential to reactively couple with functional groups on the surface of the nanotubes. The influence of the RC on the localization of MWCNTs and SWCNTs (0.5 wt.%) was investigated by transmission electron microscopy (TEM) and energy-filtered TEM. In PC/SAN blends without RC, MWCNTs are localized in the PC component. In contrast, in PC/SAN-RC, the MWCNTs localize in the SAN-RC component, depending on the RC concentration. By adjusting the MWCNT/RC ratio, the localization of the MWCNTs can be tuned. The SWCNTs behave differently compared to the MWCNTs in PC/SAN-RC blends and their localization occurs either only in the PC or in both blend components, depending on the type of the SWCNTs. CNT defect concentration and surface functionalities seem to be responsible for the localization differences.
- ItemBio-inspired deposition of electrochemically exfoliated graphene layers for electrical resistance heating applications(Bristol : IOP Publishing, 2020-12-4) Utech, Toni; Pötschke, Petra; Simon, Frank; Janke, Andreas; Kettner, Hannes; Paiva, Maria; Zimmerer, CordeliaElectrochemically exfoliated graphene (eeG) layers possess a variety of potential applications, e.g. as susceptor material for contactless induction heating in dynamic electro-magnetic fields, and as flexible and transparent electrode or resistivity heating elements. Spray coating of eeG dispersions was investigated in detail as a simple and fast method to deposit both, thin conducting layers and ring structures on polycarbonate substrates. The spray coating process was examined by systematic variation of dispersion concentration and volume applied to heated substrates. Properties of the obtained layers were characterized by UV-VIS spectroscopy, SEM and Confocal Scanning Microscopy. Electrical conductivity of eeG ring structures was measured using micro-four-point measurements. Modification of eeG with poly(dopamine) and post-thermal treatment yields in the reduction of the oxidized graphene proportion, an increase in electrical conductivity, and mechanical stabilization of the deposited thin layers. The chemical composition of modified eeG layer was analyzed via x-ray photoelectron spectroscopy pointing to the reductive behavior of poly(dopamine). Application oriented experiments demonstrate the direct electric current heating (Joule-Heating) effect of spray-coated eeG layers.
- ItemInfluence of Polyvinylpyrrolidone on Thermoelectric Properties of Melt-Mixed Polymer/Carbon Nanotube Composites(Basel : MDPI, 2023) Krause, Beate; Imhoff, Sarah; Voit, Brigitte; Pötschke, PetraFor thermoelectric applications, both p- and n-type semi-conductive materials are combined. In melt-mixed composites based on thermoplastic polymers and carbon nanotubes, usually the p-type with a positive Seebeck coefficient (S) is present. One way to produce composites with a negative Seebeck coefficient is to add further additives. In the present study, for the first time, the combination of single-walled carbon nanotubes (SWCNTs) with polyvinylpyrrolidone (PVP) in melt-mixed composites is investigated. Polycarbonate (PC), poly(butylene terephthalate) (PBT), and poly(ether ether ketone) (PEEK) filled with SWCNTs and PVP were melt-mixed in small scales and thermoelectric properties of compression moulded plates were studied. It could be shown that a switch in the S-value from positive to negative values was only possible for PC composites. The addition of 5 wt% PVP shifted the S-value from 37.8 µV/K to −31.5 µV/K (2 wt% SWCNT). For PBT as a matrix, a decrease in the Seebeck coefficient from 59.4 µV/K to 8.0 µV/K (8 wt% PVP, 2 wt% SWCNT) could be found. In PEEK-based composites, the S-value increased slightly with the PVP content from 48.0 µV/K up to 54.3 µV/K (3 wt% PVP, 1 wt% SWCNT). In addition, the long-term stability of the composites was studied. Unfortunately, the achieved properties were not stable over a storage time of 6 or 18 months. Thus, in summary, PVP is not suitable for producing long-term stable, melt-mixed n-type SWCNT composites.