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- ItemGraphene Derivatives Doped with Nickel Ferrite Nanoparticles as Excellent Microwave Absorbers in Soft Nanocomposites(Weinheim : Wiley-VCH, 2017) Pawar, Shital Patangrao; Gandi, Mounika; Arief, Injamamul; Krause, Beate; Pötschke, Petra; Bose, SuryasarathiHerein, we report the development of soft polymeric composites containing multiwall carbon nanotubes (MWNTs, 1–3 wt%) and graphene derivatives doped with nickel ferrite nanoparticles (rGO@NF, 10 wt%) as lightweight microwave absorbers. The soft nanocomposites were designed using melt-mixed blends of varying compositions of PC (polycarbonate) and SAN (poly styrene acrylonitrile) by compartmentalized functional nanoparticles in one of the components of the blend (here PC). Maximum attenuation of the incoming electromagnetic (EM) radiation mainly through absorption was achieved. The hetero-dielectric media at microscopic length scale in the PC component provided large interfaces which facilitated multiple scattering thereby attenuating the incoming EM radiation. This strategy of positioning the functional nanoparticles in one of the components in the blends resulted in significantly enhanced shielding effectiveness (SE), at any given concentration of MWNTs, in contrast to PC based composites. This enhancement in SE was realized in the special morphology of the bicomponent PC/SAN=60/40 wt% blends where both the components are continuous. The enhanced SE in co-continuous blends is due to combined effect of enhanced electrical conductivity (more precisely due to interconnected network of the nanoparticles) and the presence of a hetero-dielectric media generating large scattering interfaces. For instance, the PC/SAN (60/40 wt%) co-continuous blend containing 3 wt% MWNTs and 10 wt% rGO@NF manifested in a total shielding effectiveness (SET) of −32.3 dB (i. e. more than 99.9 % attenuation of incoming EM radiation) mainly through absorption.
- ItemEffect of Graphite Nanoplate Morphology on the Dispersion and Physical Properties of Polycarbonate Based Composites(Basel : MDPI, 2017-5-18) Müller, Michael Thomas; Hilarius, Konrad; Liebscher, Marco; Lellinger, Dirk; Alig, Ingo; Pötschke, PetraThe influence of the morphology of industrial graphite nanoplate (GNP) materials on their dispersion in polycarbonate (PC) is studied. Three GNP morphology types were identified, namely lamellar, fragmented or compact structure. The dispersion evolution of all GNP types in PC is similar with varying melt temperature, screw speed, or mixing time during melt mixing. Increased shear stress reduces the size of GNP primary structures, whereby the GNP aspect ratio decreases. A significant GNP exfoliation to individual or few graphene layers could not be achieved under the selected melt mixing conditions. The resulting GNP macrodispersion depends on the individual GNP morphology, particle sizes and bulk density and is clearly reflected in the composite's electrical, thermal, mechanical, and gas barrier properties. Based on a comparison with carbon nanotubes (CNT) and carbon black (CB), CNT are recommended in regard to electrical conductivity, whereas, for thermal conductive or gas barrier application, GNP is preferred.
- ItemPolypropylene-based melt mixed composites with singlewalled carbon nanotubes for thermoelectric applications: Switching from p-type to n-type by the addition of polyethylene glycol(Oxford : Elsevier Science, 2017) Luo, Jinji; Cerretti, Giacomo; Krause, Beate; Zhang, Long; Otto, Thomas; Jenschke, Wolfgang; Ullrich, Mathias; Tremel, Wolfgang; Voit, Brigitte; Pötschke, PetraThe thermoelectric properties of melt processed conductive nanocomposites consisting of an insulating polypropylene (PP) matrix filled with singlewalled carbon nanotubes (CNTs) and copper oxide (CuO) were evaluated. An easy and cheap route to switch p-type composites into n-type was developed by adding polyethylene glycol (PEG) during melt mixing. At the investigated CNT concentrations of 0.8 wt% and 2 wt% (each above the electrical percolation threshold of ∼0.1 wt%), and a fixed CuO content of 5 wt%, the PEG addition converted p-type composites (positive Seebeck coefficient (S)) into n-type (negative S). PEG was also found to improve the filler dispersion inside the matrix. Two composites were prepared: P-type polymer/CNT composites with high S (up to 45 μV/K), and n-type composites (with S up to −56 μV/K) through the addition of PEG. Two prototypes with 4 and 49 thermocouples of these p- and n-type composites were fabricated, and delivered an output voltage of 21 mV and 110 mV, respectively, at a temperature gradient of 70 K.
- ItemImpact of synthesis temperature on morphology, rheology and electromagnetic interference shielding of CVD-grown carbon nanotube/polyvinylidene fluoride nanocomposites(Lausanne : Elsevier Sequoia, 2017) Mirkhani, Seyyed Alireza; Arjmand, Mohammad; Sadeghi, Soheil; Krause, Beate; Pötschke, Petra; Sundararaj, UttandaramanEmploying chemical vapor deposition technique, multi-walled carbon nanotubes (CNTs) were synthesized over Fe catalyst at a broad range of temperatures, i.e. 550° C to 950° C (at 100° C intervals). CNTs were melt-mixed into a polyvinylidene fluoride (PVDF) matrix at various loadings, and then compression molded. Surprisingly, despite the ascending trend of CNT powder conductivity with the synthesis temperature, the nanocomposites made with CNT synthesized at 650° C had significantly lower percolation threshold (around 0.4 wt%) and higher electromagnetic interference shielding effectiveness (EMI SE) (20.3 dB over the X-band for 3.5 wt% CNT and 1.1 mm thickness) than the other temperatures. Exhaustive characterization studies were conducted on both CNTs and composites to unveil their morphological and electrical characteristics. Superior EMI shielding of CNT650° C was attributed to a combination of high carbon purity, aspect ratio, crystallinity, and moderate powder conductivity along with decent state of dispersion within the PVDF matrix.