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- 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.
- ItemInN nanowires: Growth and optoelectronic properties(Basel : MDPI AG, 2012) Calarco, R.An overview on InN nanowires, fabricated using either a catalyst-free molecular beam epitaxy method or a catalyst assisted chemical vapor deposition process, is provided. Differences and similarities of the nanowires prepared using the two techniques are presented. The present understanding of the growth and of the basic optical and transport properties is discussed.
- ItemExperimental Hall electron mobility of bulk single crystals of transparent semiconducting oxides(Cambridge [u.a.] : Cambridge Univ. Press, 2021) Galazka, Zbigniew; Irmscher, Klaus; Pietsch, Mike; Ganschow, Steffen; Schulz, Detlev; Klimm, Detlef; Hanke, Isabelle M.; Schroeder, Thomas; Bickermann, MatthiasWe provide a comparative study of basic electrical properties of bulk single crystals of transparent semiconducting oxides (TSOs) obtained directly from the melt (9 compounds) and from the gas phase (1 compound), including binary (β-Ga2O3, In2O3, ZnO, SnO2), ternary (ZnSnO3, BaSnO3, MgGa2O4, ZnGa2O4), and quaternary (Zn1−xMgxGa2O4, InGaZnO4) systems. Experimental outcome, covering over 200 samples measured at room temperature, revealed n-type conductivity of all TSOs with free electron concentrations (ne) between 5 × 1015 and 5 × 1020 cm−3 and Hall electron mobilities (μH) up to 240 cm2 V−1 s−1. The widest range of ne values was achieved for β-Ga2O3 and In2O3. The most electrically conducting bulk crystals are InGaZnO4 and ZnSnO3 with ne > 1020 cm−3 and μH > 100 cm2 V−1 s−1. The highest μH values > 200 cm2 V−1 s−1 were measured for SnO2, followed by BaSnO3 and In2O3 single crystals. In2O3, ZnO, ZnSnO3, and InGaZnO4 crystals were always conducting, while others could be turned into electrical insulators.
- ItemThermal conductivity and electrical resistivity of melt-mixed polypropylene composites containing mixtures of carbon-based fillers(Basel : MDPI, 2019) Krause, Beate; Rzeczkowski, Piotr; Pötschke, PetraMelt-mixed composites based on polypropylene (PP) with various carbon-based fillers were investigated with regard to their thermal conductivity and electrical resistivity. The composites were filled with up to three fillers by selecting combinations of graphite nanoplatelets (GNP), carbon fibers (CF), carbon nanotubes (CNT), carbon black (CB), and graphite (G) at a constant filler content of 7.5 vol%. The thermal conductivity of PP (0.26 W/(m·K)) improved most using graphite nanoplatelets, whereas electrical resistivity was the lowest when using multiwalled CNT. Synergistic effects could be observed for different filler combinations. The PP composite, which contains a mixture of GNP, CNT, and highly structured CB, simultaneously had high thermal conductivity (0.5 W/(m·K)) and the lowest electrical volume resistivity (4 Ohm·cm).
- ItemMelt mixed SWCNT-polypropylene composites with very low electrical percolation(Oxford : Elsevier Science, 2016) Krause, Beate; Pötschke, Petra; Ilin, Evgeniy; Predtechenskiy, MikhailSinglewalled carbon nanotube material of the type TUBALL™ (OCSiAl) was used to prepare composites with polypropylene by melt mixing using a conical twin screw micro-compounder. The compression moulded composites showed electrical percolation between 0.075 and 0.1 wt % and achieved volume resistivity values lower than 1 kOhm-cm already at 0.8 wt % loading. Light microscopy and scanning electron microscopy revealed good distribution and dispersion into small diameter bundles as well as retained high nanotube length. In connection with the very low percolation threshold this indicates that the SWCNT material shows an exceptionally good dispersibility which may be due to relatively high nanotube diameters with a mean value of 1.6 nm. In tensile tests already 0.1 wt % nanotube additions resulted in slight increase in Young's modulus and maximum stress. Tuball™ SWCNT material seems to be very promising for conductivity enhancement.
- ItemTowards an open-source landscape for 3-D CSEM modelling(Oxford : Oxford Univ. Press, 2021) Werthmüller, Dieter; Rochlitz, Raphael; Castillo-Reyes, Octavio; Heagy, LindseyLarge-scale modelling of 3-D controlled-source electromagnetic (CSEM) surveys used to be feasible only for large companies and research consortia. This has changed over the last few years, and today there exists a selection of different open-source codes available to everyone. Using four different codes in the Python ecosystem, we perform simulations for increasingly complex models in a shallow marine setting. We first verify the computed fields with semi-analytical solutions for a simple layered model. Then we validate the responses of a more complex block model by comparing results obtained from each code. Finally, we compare the responses of a real-world model with results from the industry. On the one hand, these validations show that the open-source codes are able to compute comparable CSEM responses for challenging, large-scale models. On the other hand, they show many general and method-dependent problems that need to be faced for obtaining accurate results. Our comparison includes finite-element and finite-volume codes using structured rectilinear and octree meshes as well as unstructured tetrahedral meshes. Accurate responses can be obtained independently of the chosen method and the chosen mesh type. The runtime and memory requirements vary greatly based on the choice of iterative or direct solvers. However, we have found that much more time was spent on designing the mesh and setting up the simulations than running the actual computation. The challenging task is, irrespective of the chosen code, to appropriately discretize the model. We provide three models, each with their corresponding discretization and responses of four codes, which can be used for validation of new and existing codes. The collaboration of four code maintainers trying to achieve the same task brought in the end all four codes a significant step further. This includes improved meshing and interpolation capabilities, resulting in shorter runtimes for the same accuracy. We hope that these results may be useful for the CSEM community at large and that we can build over time a suite of benchmarks that will help to increase the confidence in existing and new 3-D CSEM codes.
- 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.
- ItemThe influence of the blend ratio in PA6/PA66/MWCNT blend composites on the electrical and thermal properties(Basel : MDPI, 2019) Krause, Beate; Kroschwald, Lisa; Pötschke, PetraIt is known that the percolation threshold of polyamide 6 (PA6)/multiwalled carbon nanotube (MWCNT) composites is higher than that of PA66/MWCNT composites under the same mixing conditions and melt viscosity. A series of blends of PA6 and PA66 containing 1 wt % MWCNTs have been prepared to investigate this phenomenon. At contents up to 20 wt % PA66, the blends were not electrically conductive. The electrical resistivity dropped to 109 Ohm∙cm for PA66/PA6 30/70 blends. The resistivity was 105 Ohm∙cm at higher PA66 contents. Differential scanning calorimetry was used to investigate the thermal behavior of blends. The glass transition temperature was almost constant for all blend compositions, indicating that the amorphous phases are miscible. The MWCNT addition influenced the crystallization of PA66 much more than the PA6 crystallization. A heterogeneous crystallization of the polyamide in PA66/PA6 blends took place, and the MWCNTs were mainly localized in the earlier crystallizing PA66 phase. Thus, the formation of the nanotube network and thus the electrical volume resistivity of the PA6/PA66 blends with 1 wt % MWCNTs is significantly influenced by the crystallization behavior. In PA66/PA6 blends up to 60 wt %, the more expensive PA66 can be replaced by the cheaper PA6 while retaining its electrical properties