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- ItemMagnetization Dynamics of an Individual Single-Crystalline Fe-Filled Carbon Nanotube(Weinheim : Wiley-VCH, 2019) Lenz, Kilian; Narkowicz, Ryszard; Wagner, Kai; Reiche, Christopher F.; Körner, Julia; Schneider, Tobias; Kákay, Attila; Schultheiss, Helmut; Weissker, Uhland; Wolf, Daniel; Suter, Dieter; Büchner, Bernd; Fassbender, Jürgen; Mühl, Thomas; Lindner, JürgenThe magnetization dynamics of individual Fe-filled multiwall carbon-nanotubes (FeCNT), grown by chemical vapor deposition, are investigated by microresonator ferromagnetic resonance (FMR) and Brillouin light scattering (BLS) microscopy and corroborated by micromagnetic simulations. Currently, only static magnetometry measurements are available. They suggest that the FeCNTs consist of a single-crystalline Fe nanowire throughout the length. The number and structure of the FMR lines and the abrupt decay of the spin-wave transport seen in BLS indicate, however, that the Fe filling is not a single straight piece along the length. Therefore, a stepwise cutting procedure is applied in order to investigate the evolution of the ferromagnetic resonance lines as a function of the nanowire length. The results show that the FeCNT is indeed not homogeneous along the full length but is built from 300 to 400 nm long single-crystalline segments. These segments consist of magnetically high quality Fe nanowires with almost the bulk values of Fe and with a similar small damping in relation to thin films, promoting FeCNTs as appealing candidates for spin-wave transport in magnonic applications. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemComplement activation by carbon nanotubes and its influence on the phagocytosis and cytokine response by macrophages(Amsterdam [u.a.] : Elsevier, 2014) Pondman, K.M.; Sobik, M.; Nayak, A.; Tsolaki, A.G.; Jäkel, A.; Flahaut, E.; Hampel, S.; ten Haken, B.; Sim, R.B.; Kishore, U.Carbon nanotubes (CNTs) have promised a range of applications in biomedicine. Although influenced by the dispersants used, CNTs are recognized by the innate immune system, predominantly by the classical pathway of the complement system. Here, we confirm that complement activation by the CNT used continues up to C3 and C5, indicating that the entire complement system is activated including the formation of membrane-attack complexes. Using recombinant forms of the globular regions of human C1q (gC1q) as inhibitors of CNT-mediated classical pathway activation, we show that C1q, the first recognition subcomponent of the classical pathway, binds CNTs via the gC1q domain. Complement opsonisation of CNTs significantly enhances their uptake by U937 cells, with concomitant downregulation of pro-inflammatory cytokines and up-regulation of anti-inflammatory cytokines in both U937 cells and human monocytes. We propose that CNT-mediated complement activation may cause recruitment of cellular infiltration, followed by phagocytosis without inducing a pro-inflammatory immune response. From the Clinical Editor: This study highlights the importance of the complement system in response to carbon nanontube administration, suggesting that the ensuing complement activation may cause recruitment of cellular infiltration, followed by phagocytosis without inducing a pro-inflammatory immune response.
- 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.
- ItemDegradation analysis of tribologically loaded carbon nanotubes and carbon onions([London] : Macmillan Publishers Limited, 2023) MacLucas, T.; Grützmacher, P.; Husmann, S.; Schmauch, J.; Keskin, S.; Suarez, S.; Presser, V.; Gachot, C.; Mücklich, F.Coating laser-patterned stainless-steel surfaces with carbon nanotubes (CNT) or carbon onions (CO) forms a tribological system that provides effective solid lubrication. Lubricant retention represents the fundamental mechanism of this system, as storing the particles inside the pattern prevents lubricant depletion in the contact area. In previous works, we used direct laser interference patterning to create line patterns with three different structural depths on AISI 304 stainless-steel platelets. Electrophoretic deposition subsequently coated the patterned surfaces with either CNTs or COs. Ball-on-disc friction tests were conducted to study the effect of structural depth on the solid lubricity of as-described surfaces. The results demonstrated that the shallower the textures, the lower the coefficient of friction, regardless of the applied particle type. This follow-up study examines the carbon nanoparticles’ structural degradation after friction testing on substrates patterned with different structural depths (0.24, 0.36, and 0.77 µm). Raman characterization shows severe degradation of both particle types and is used to classify their degradation state within Ferrari’s three-stage amorphization model. It was further shown that improving CNT lubricity translates into increasing particle defectivity. This is confirmed by electron microscopy, which shows decreasing crystalline domains. Compared to CNTs, CO-derived tribofilms show even more substantial structural degradation.
- ItemMethods to characterize the dispersability of carbon nanotubes and their length distribution(Weinheim : Wiley-VCH Verl., 2012) Krause, Beate; Mende, Mandy; Petzold, Gudrun; Boldt, Regine; Pötschke, PetraTwo main properties of carbon nanotube (CNT) materials are discussed in this contribution. First, a method to characterize the dispersability of CNT materials in aqueous surfactant solutions in presented, which also allows conclusions towards the dispersability in other media, like polymer melts. On the other hand it is shown, how the length of CNTs before and after processing, e.g., after melt mixing with thermoplastics, can be quantified. Both methods are illustrated with examples and the practical relevance is shown. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
- ItemMelt-mixed PP/MWCNT composites: Influence of CNT incorporation strategy and matrix viscosity on filler dispersion and electrical resistivity(Basel : MDPI, 2019) Pötschke, Petra; Mothes, Fanny; Krause, Beate; Voit, BrigitteSmall-scale melt mixing was performed for composites based on polypropylene (PP) and 0.5–7.5 wt % multiwalled carbon nanotubes (MWCNT) to determine if masterbatch (MB) dilution is a more effective form of nanofiller dispersion than direct nanotube incorporation. The methods were compared using composites of five different PP types, each filled with 2 wt % MWCNTs. After the determination of the specific mechanical energy (SME) input in the MB dilution process, the direct-incorporation mixing time was adjusted to achieve comparable SME values. Interestingly, the electrical resistivity of MB-prepared samples with 2 wt % MWCNTs was higher than that of those prepared using direct incorporation—despite their better dispersion—suggesting more pronounced MWCNT shortening in the two-step procedure. In summary, this study on PP suggests that the masterbatch approach is suitable for the dispersion of MWCNTs and holds advantages in nanotube dispersion, albeit at the cost of slightly increased electrical resistivity.
- ItemSurface defects reduce Carbon Nanotube toxicity in vitro(Amsterdam [u.a.] : Elsevier Science, 2019) Requardt, Hendrik; Braun, Armin; Steinberg, Pablo; Hampel, Silke; Hansen, TanjaThe cytotoxicity of two different types of Multi-walled Carbon Nanotubes (MWCNTs)in A549 lung epithelial cells and HepG2 hepatocytes was investigated. One MWCNT still contained iron that was used as a catalyst during production, while the other one had all iron removed in a post-production heat treatment resulting in significantly fewer surface defects. The WST-8 assay was applied to test cell viability. To check the integrity of the cell membrane, we performed the lactate dehydrogenases assay (LDH)and measured the cellular production of reactive oxygen species (ROS). Finally, to examine cell proliferation, we conducted a cell cycle analysis. The results showed a dose- and time-dependent decrease in cell viability for both MWCNTs in both cell types. Moreover, a dose- and time-dependent increase in LDH leakage was detected, thereby indicating a decreased membrane integrity. The production of ROS was significantly increased in the case of the heat-treated MWCNTs. The heat-treated MWCNTs showed significantly stronger adverse effects when compared to the non-treated MWCNTs. Additionally, the heat-treated MWCNTs induced a dose-dependent cell cycle arrest in A549 cells. Both MWCNTs induced a significant cytotoxicity, whereby the heat treatment, leading to a decrease in surface defects, further increased the indicated adverse effects. © 2019 The Authors
- 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.
- ItemFe1-xNix alloy nanoparticles encapsulated inside carbon nanotubes: Controlled synthesis, structure and magnetic properties(Basel : MDPI AG, 2018) Ghunaim, R.; Damm, C.; Wolf, D.; Lubk, A.; Büchner, B.; Mertig, M.; Hampel, S.In the present work, different synthesis procedures have been demonstrated to fill carbon nanotubes (CNTs) with Fe1-xNix alloy nanoparticles (x = 0.33, 0.5). CNTs act as templates for the encapsulation of magnetic nanoparticles, and provide a protective shield against oxidation as well as prevent nanoparticles agglomeration. By variation of the reaction parameters, the purity of the samples, degree of filling, the composition and size of filling nanoparticles have been tailored and therefore the magnetic properties. The samples were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Bright-field (BF) TEM tomography, X-ray powder diffraction, superconducting quantum interference device (SQUID) and thermogravimetric analysis (TGA). The Fe1-x Nix-filled CNTs show a huge enhancement in the coercive fields compared to the corresponding bulk materials, which make them excellent candidates for several applications such as magnetic storage devices.
- ItemHybrid conductive filler/polycarbonate composites with enhanced electrical and thermal conductivities for bipolar plate applications(Manchester, NH : Wiley, 2019) Naji, Ahmed; Krause, Beate; Pötschke, Petra; Ameli, AmirConductive polymer composites (CPCs) with high electrical and thermal conductivities are demanded for bipolar plates of fuel cells. In this work, CPCs of polycarbonate (PC) filled with carbon nanotube (CNT), carbon fiber (CF), graphite (G), and their double and triple hybrids were prepared using solution casting method followed by compression molding. The results showed that the electrical percolation thresholds for the PC-CNT and PC-CF were ~1 wt% and ~10 wt%, respectively, while no clear threshold was found for PC-G composites. Addition of 3–5 wt% CNT improved the electrical conductivity of PC-CF and PC-G systems up to 6 orders of magnitude and enhanced the thermal conductivity as much as 65%. The results of triple hybrid CPCs (with constant loading of 63 wt%) indicated that the combination of highest electrical and thermal conductivities is achieved when the CF and CNT loadings were near their percolation thresholds. Therefore, a triple filler system of 3 wt% CNT, 10 wt% CF, and 50 wt% G resulted in a composite with the through-plane and in-plane electrical conductivity, and thermal conductivity values of 12.8 S/cm, 8.3 S/cm, and 1.7 W/m•K, respectively. The results offer a combination of properties surpassing the existing values and suitable for high-conductivity applications such as bipolar plates. POLYM. COMPOS., 40:3189–3198, 2019. © 2018 Society of Plastics Engineers.