Preparation And Properties Of Carbon Nanotube/Polymer Composites

In this paper, the electrical properties and temperature coefficient effects of the multi-walled carbon nanotube/poly(vinylidene fluoride) (MWCNT/PVDF) composites were investigated. The carboxylic and ester functionalized MWCNT were prepared and the pristine, carboxylic, ester functionalized MWCNT/PVDF composites were fabricated by simple physical blending, cold-press, and heat treatment technology. The percolation thresholds of the three kinds of composites are approximately equal, about 3.8 vol%. The conductivity of the pristine MWCNT/PVDF composites increases remarkably near the percolation threshold, and exhibits a typical insulator-conductor transition. However, the conductivity of the chemically functionalized MWCNT/PVDF composites increases slowly with increasing the MWCNT volume fraction. The dielectric constants increase remarkably after the percolation threshold. However, the largest dielectric constant of these three kinds of composites is different. The largest dielectric constant of the pristine MWCNT/PVDF composites is 1700 with 6 vol% MWCNTs, while it reaches 3600 for carboxylic functionalized MWCNT/PVDF composites with about 8 vol% MWCNTs, and 2400 for ester functionalized MWCNT/PVDF composites with about 6.5 vol% MWCNTs. The positive temperature coefficient (PTC) and negative temperature coefficient (NTC) effects of these three kinds of composites are all small. However, the melting point of the chemically functionalized MWCNT/PVDF composites is larger than that of the pristine MWCNT/PVDF composites. The temperature dependence of the dielectric properties of these three kinds of MWCNT/PVDF composites is basically coincident. The dielectric constants of these composites increase with increasing temperature at low frequency, and then decrease when the temperature further increases up to about 140℃. However, the dielectric constants increase again at 180℃, which all can be attributed to the thermal expansion of the matrix and the change of the conduct net in these composites.