Large dielectric constant of the chemically functionalized carbon nanotube/polymer composites

Pristine, carboxylic and ester functionalized multi-walled carbon nanotube (MWCNT)/poly(vinylidene fluoride) (PVDF) composites were fabricated by evaporating suspensions of the nanotubes in PVDF. Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) showed that carboxylic groups and ester groups had been introduced on the surface of MWCNTs. The Raman spectroscopy showed that the amorphous carbon materials and impurities had decreased by chemical functionalizations. The electrical conductivity and dielectric properties of the composites were investigated. The percolation thresholds of the pristine, carboxylic and ester functionalized MWCNT/PVDF composites are approximately equal, about 3.8 vol%, but the dielectric constants are enhanced significantly. The largest dielectric constant of 3600 is obtained in the carboxylic functionalized MWCNT/PVDF composite with 8 vol% MWCNT at 1 kHz, which can be attributed to the preparation procedure and the interface effect between the MWCNTs and the polymer.