Effects of synthesis catalyst and temperature on broadband dielectric properties of nitrogen-doped carbon nanotube/polyvinylidene fluoride nanocomposites

This study reports on nitrogen-doped carbon nanotube (N-CNT)/polymer nanocomposites exhibiting relatively high and frequency independent real permittivity (epsilon') together with low dielectric loss (tan delta). 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 degrees 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 degrees C and 950 degrees 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 degrees) (C)/PVDF nanocomposites exhibited an insulative behavior with epsilon' = 23.12 and tan delta = 0.05 at 1 kHz, a combination superior to that of PVDF, i.e., epsilon' = 8.4 and tan delta = 0.03 and to those of percolative nanocomposites, e.g., epsilon' = 71.20 and tan delta = 63.20 for 3.5 wt% (N-CNT)(Fe/750 degrees C)/PVDF. Also, the relationships between the dielectric properties, N-CNT structure, and nanocomposite morphology were identified. (C) 2016 Elsevier Ltd. All rights reserved.