2016, Ameli, A., Arjmand, M., Pötschke, Petra, Krause, Beate, Sundararaj, U.

This study reports on nitrogen-doped carbon nanotube (N-CNT)/polymer nanocomposites exhibiting relatively high and frequency independent real permittivity (ϵ′) together with low dielectric loss (tan δ). N-CNTs were synthesized by chemical vapor deposition, and their nanocomposites were prepared by melt-mixing with polyvinylidene fluoride (PVDF). In the synthesis of N-CNTs, three catalysts of Co, Fe and Ni, and three temperatures of 650, 750 and 950 °C were employed. The morphology, aspect ratio, synthesis yield, remaining residue, nitrogen content, nitrogen bonding type, and powder conductivity of N-CNTs, and the morphology, polar crystalline phase, and broadband dielectric properties of N-CNT/PVDF nanocomposites were investigated. The results revealed that by proper selection of synthesis catalyst (Fe) and temperature (650 °C and 950 °C), nitrogen doping generated polarizable nanotubes via providing local polarization sites, and resulted in nanocomposites with favorable dielectric properties for charge storage applications at N-CNT loadings as low as 1.0 wt%. As a result, 3.5 wt% (N-CNT)Fe/950°C/PVDF nanocomposites exhibited an insulative behavior with ϵ' = 23.12 and tan δ = 0.05 at 1 kHz, a combination superior to that of PVDF, i.e., ϵ' = 8.4 and tan δ = 0.03 and to those of percolative nanocomposites, e.g., ϵ' = 71.20 and tan δ = 63.20 for 3.5 wt% (N-CNT)Fe/750°C/PVDF. Also, the relationships between the dielectric properties, N-CNT structure, and nanocomposite morphology were identified.

2021-3-1, Gültner, Marén, Boldt, Regine, Formanek, Petr, Fischer, Dieter, Simon, Frank, Pötschke, Petra

Co-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.