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- ItemCuxCo1-xFe2O4 (x = 0.33, 0.67, 1) Spinel Ferrite Nanoparticles Based Thermoplastic Polyurethane Nanocomposites with Reduced Graphene Oxide for Highly Efficient Electromagnetic Interference Shielding(Basel : Molecular Diversity Preservation International (MDPI), 2022-2-26) Anju; Yadav, Raghvendra Singh; Pötschke, Petra; Pionteck, Jürgen; Krause, Beate; Kuřitka, Ivo; Vilčáková, Jarmila; Škoda, David; Urbánek, Pavel; Machovský, Michal; Masař, Milan; Urbánek, MichalCuxCo1-x Fe2O4 (x = 0.33,0.67,1)-reduced graphene oxide (rGO)-thermoplastic polyurethane (TPU) nanocomposites exhibiting highly efficient electromagnetic interference (EMI) shielding were prepared by a melt-mixing approach using a microcompounder. Spinel ferrite Cu0.33Co0.67Fe2O4 (Cu-CoF1), Cu0.67Co0.33Fe2O4 (CuCoF2) and CuFe2O4 (CuF3) nanoparticles were synthesized using the sonochemical method. The CuCoF1 and CuCoF2 exhibited typical ferromagnetic features, whereas CuF3 displayed superparamagnetic characteristics. The maximum value of EMI total shielding effectiveness (SEt) was noticed to be 42.9 dB, 46.2 dB, and 58.8 dB for CuCoF1-rGO-TPU, CuCoF2-rGO-TPU, and CuF3-rGO-TPU nanocomposites, respectively, at a thickness of 1 mm. The highly efficient EMI shielding performance was attributed to the good impedance matching, conductive, dielectric, and magnetic loss. The demonstrated nanocomposites are promising candidates for a lightweight, flexible, and highly efficient EMI shielding material.
- 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.
- ItemFerric Ions Crosslinked Epoxidized Natural Rubber Filled with Carbon Nanotubes and Conductive Carbon Black Hybrid Fillers(Basel : MDPI, 2022-10-18) Damampai, Kriengsak; Pichaiyut, Skulrat; Stöckelhuber, Klaus Werner; Das, Amit; Nakason, CharoenNatural rubber with 50 mol % epoxidation (ENR-50) was filled with carbon nanotubes (CNTs) and conductive carbon black (CCB) hybrid fillers with various CCB loadings of 2.5, 5.0, 7.0, 10.0 and 15.0 phr, and the compounds were mixed with ferric ion (Fe3+) as a crosslinking agent. The ENRs filled exclusively with CNTs, and CNT–CCB hybrid fillers exhibited typical curing curves at different CCB loadings, i.e., increasing torque with time and thus crosslinked networks. Furthermore, the incorporation of CNT–CCB hybrid fillers and increasing CCB loadings caused an enhancement of tensile properties (modulus and tensile strength) and crosslink densities, which are indicated by the increasing torque difference and the crosslink densities. The crosslink densities are determined by swelling and temperature scanning stress relaxation (TSSR). Increasing CCB loadings also caused a significant improvement in bound rubber content, filler–rubber interactions, thermal resistance, glass transition temperature (Tg) and electrical conductivity. A combination of 7 phr CNT and CCB with loading higher than 2.5 phr gave superior properties to ENR vulcanizates. Furthermore, the secondary CCB filler contributes to the improvement of CNT dispersion in the ENR matrix by networking the CNT capsules and forming CNT–CCB–CNT pathways and thus strong CNT–CCB networks, indicating the improvement in the tensile properties, bound rubber content and dynamic properties of the ENR composites. Moreover, higher electrical conductivity with a comparatively low percolation threshold of the hybrid composites was found as compared to the ENR filled with CNTs without CCB composite. The superior mechanical and other properties are due to the finer dispersion and even distribution of CNT–CCB hybrid fillers in the ENR matrix.
- ItemThermoelectric Performance of Polypropylene/Carbon Nanotube/Ionic Liquid Composites and Its Dependence on Electron Beam Irradiation(Basel : MDPI, 2022-1-11) Voigt, Oliver; Krause, Beate; Pötschke, Petra; Müller, Michael T.; Wießner, SvenThe thermoelectric behavior of polypropylene (PP) based nanocomposites containing single walled carbon nanotubes (SWCNTs) and five kinds of ionic liquids (Ils) dependent on composite composition and electron beam irradiation (EB) was studied. Therefore, several samples were melt-mixed in a micro compounder, while five Ils with sufficiently different anions and/or cations were incorporated into the PP/SWCNT composites followed by an EB treatment for selected composites. Extensive investigations were carried out considering the electrical, thermal, mechanical, rheological, morphological and, most significantly, thermoelectric properties. It was found that it is possible to prepare n-type melt-mixed polymer composites from p-type commercial SWCNTs with relatively high Seebeck coefficients when adding four of the selected Ils. The highest Seebeck coefficients achieved in this study were +49.3 µV/K (PP/2 wt.% SWCNT) for p-type composites and −27.6 µV/K (PP/2 wt.% SWCNT/4 wt.% IL type AMIM Cl) for n-type composites. Generally, the type of IL is decisive whether p-or n-type thermoelectric behavior is achieved. After IL addition higher volume conductivity could be reached. Electron beam treatment of PP/SWCNT leads to increased values of the Seebeck coefficient, whereas the EB treated sample with IL (AMIM Cl) shows a less negative Seebeck coefficient value.
- ItemDoes the Type of Polymer and Carbon Nanotube Structure Control the Electromagnetic Shielding in Melt-Mixed Polymer Nanocomposites?(Basel : MDPI, 2020-1-15) Biswas, Sourav; Muzata, Tanyaradzwa S.; Krause, Beate; Rzeczkowski, Piotr; Pötschke, Petra; Bose, SuryasarathiA suitable polymer matrix and well dispersed conducting fillers forming an electrically conducting network are the prime requisites for modern age electromagnetic shield designing. An effective polymer-based shield material is designed that can attenuate 99.9% of incident electromagnetic (EM) radiation at a minimum thickness of <0.5 mm. This is accomplished by the choice of a suitable partially crystalline polymer matrix while comparing non-polar polypropylene (PP) with polar polyvinylidene fluoride (PVDF) and a best suited filler nanomaterial by comparing different types of carbon nanotubes such as; branched, single-walled and multi-walled carbon nanotubes, which were added in only 2 wt %. Different types of interactions (polar-polar and CH-π and donor-acceptor) make b-MWCNT more dispersible in the PVDF matrix, which together with high crystallinity resulted in the best electrical conductivity and electromagnetic shielding ability of this composite. This investigation additionally conceals the issues related to the thickness of the shield material just by stacking individual thin nanocomposite layers containing different carbon nanotube (CNT) types with 0.3 mm thickness in a simple manner and finally achieves 99.999% shielding efficiency at just 0.9 mm thickness when using a suitable order of the different PVDF based nanocomposites.
- ItemBlind Super-Resolution Approach for Exploiting Illumination Variety in Optical-Lattice Illumination Microscopy(Washington, DC : ACS Publications, 2021) Samanta, Krishnendu; Sarkar, Swagato; Acuña, Sebastian; Joseph, Joby; Ahluwalia, Balpreet Singh; Agarwal, KrishnaOptical-lattice illumination patterns help in pushing high spatial frequency components of the sample into the optical transfer function of a collection microscope. However, exploiting these high-frequency components require precise knowledge of illumination if reconstruction approaches similar to structured illumination microscopy are employed. Here, we present an alternate blind reconstruction approach that can provide super-resolution without the requirement of extra frames. For this, the property of exploiting temporal fluctuations in the sample emissions using “multiple signal classification algorithm” is extended aptly toward using spatial fluctuation of phase-modulated lattice illuminations for super-resolution. The super-resolution ability is shown for sinusoidal and multiperiodic lattice with approximately 3- and 6-fold resolution enhancements, respectively, over the diffraction limit. © 2021 The Authors. Published by American Chemical Society
- ItemPodosome-Driven Defect Development in Lamellar Bone under the Conditions of Senile Osteoporosis Observed at the Nanometer Scale(Washington, DC : ACS Publications, 2021) Simon, Paul; Pompe, Wolfgang; Bobeth, Manfred; Worch, Hartmut; Kniep, Rüdiger; Formanek, Petr; Hild, Anne; Wenisch, Sabine; Sturm, ElenaThe degradation mechanism of human trabecular bone harvested from the central part of the femoral head of a patient with a fragility fracture of the femoral neck under conditions of senile osteoporosis was investigated by high-resolution electron microscopy. As evidenced by light microscopy, there is a disturbance of bone metabolism leading to severe and irreparable damages to the bone structure. These defects are evoked by osteoclasts and thus podosome activity. Podosomes create typical pit marks and holes of about 300-400 nm in diameter on the bone surface. Detailed analysis of the stress field caused by the podosomes in the extracellular bone matrix was performed. The calculations yielded maximum stress in the range of few megapascals resulting in formation of microcracks around the podosomes. Disintegration of hydroxyapatite and free lying collagen fibrils were observed at the edges of the plywood structure of the bone lamella. At the ultimate state, the disintegration of the mineralized collagen fibrils to a gelatinous matrix comes along with a delamination of the apatite nanoplatelets resulting in a brittle, porous bone structure. The nanoplatelets aggregate to big hydroxyapatite plates with a size of up to 10 x 20 μm2. The enhanced plate growth can be explained by the interaction of two mechanisms in the ruffled border zone: the accumulation of delaminated hydroxyapatite nanoplatelets near clusters of podosomes and the accelerated nucleation and random growth of HAP nanoplatelets due to a nonsufficient concentration of process-directing carboxylated osteocalcin cOC. © 2021 The Authors. Published by American Chemical Society.
- ItemGas-Phase Fluorination on PLA Improves Cell Adhesion and Spreading(Washington, DC : Soc., 2020) Schroepfer, Michaela; Junghans, Frauke; Voigt, Diana; Meyer, Michael; Breier, Anette; Schulze-Tanzil, Gundula; Prade, InaFor the regeneration or creation of functional tissues, biodegradable biomaterials including polylactic acid (PLA) are widely preferred. Modifications of the material surface are quite common to improve cell-material interactions and thereby support the biological outcome. Typical approaches include a wet chemical treatment with mostly hazardous substances or a functionalization with plasma. In the present study, gas-phase fluorination was applied to functionalize the PLA surfaces in a simple and one-step process. The biological response including biocompatibility, cell adhesion, cell spreading, and proliferation was analyzed in cell culture experiments with fibroblasts L929 and correlated with changes in the surface properties. Surface characterization methods including surface energy and isoelectric point measurements, X-ray photoelectron spectroscopy, and atomic force microscopy were applied to identify the effects of fluorination on PLA. Gas-phase fluorination causes the formation of C-F bonds in the PLA backbone, which induce a shift to a more hydrophilic and polar surface. The slightly negatively charged surface dramatically improves cell adhesion and spreading of cells on the PLA even with low fluorine content. The results indicate that this improved biological response is protein-but not integrin-dependent. Gas-phase fluorination is therefore an efficient technique to improve cellular response to biomaterial surfaces without losing cytocompatibility. Copyright © 2020 American Chemical Society.
- ItemBiomaterial based strategies to reconstruct the nigrostriatal pathway in organotypic slice co-cultures(Amsterdam [u.a.] : Elsevier, 2021) Ucar, Buket; Kajtez, Janko; Foidl, Bettina M.; Eigel, Dimitri; Werner, Carsten; Long, Katherine R.; Emnéus, Jenny; Bizeau, Joëlle; Lomora, Mihai; Pandit, Abhay; Newland, Ben; Humpel, ChristianProtection or repair of the nigrostriatal pathway represents a principal disease-modifying therapeutic strategy for Parkinson's disease (PD). Glial cell line-derived neurotrophic factor (GDNF) holds great therapeutic potential for PD, but its efficacious delivery remains difficult. The aim of this study was to evaluate the potential of different biomaterials (hydrogels, microspheres, cryogels and microcontact printed surfaces) for reconstructing the nigrostriatal pathway in organotypic co-culture of ventral mesencephalon and dorsal striatum. The biomaterials (either alone or loaded with GDNF) were locally applied onto the brain co-slices and fiber growth between the co-slices was evaluated after three weeks in culture based on staining for tyrosine hydroxylase (TH). Collagen hydrogels loaded with GDNF slightly promoted the TH+ nerve fiber growth towards the dorsal striatum, while GDNF loaded microspheres embedded within the hydrogels did not provide an improvement. Cryogels alone or loaded with GDNF also enhanced TH+ fiber growth. Lines of GDNF immobilized onto the membrane inserts via microcontact printing also significantly improved TH+ fiber growth. In conclusion, this study shows that various biomaterials and tissue engineering techniques can be employed to regenerate the nigrostriatal pathway in organotypic brain slices. This comparison of techniques highlights the relative merits of different technologies that researchers can use/develop for neuronal regeneration strategies. © 2020
- 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.