Temperature-dependent transport properties in the semiconducting regime of nanoparticle carbon-polyimide composite films

Temperature-depend ant electrical conductivity characteristics of carbon black (CB)-polyimide (PI) nanocomposite films with carbon contents from 0% to 8% v/v in the temperature range 300-425K are reported. Semiconducting behaviour was observed for all the carbon concentrations studied. The temperature-dependent electrical conductivity has more than one contributing factor such as the enhancement in conductivity through activation of charge carriers, and the decrease in conductivity arising from large differences in the coefficients of thermal expansion of the polymer and carbon nanoparticles. A methodology was developed to evaluate the conductivity decrease arising from the thermal expansion characteristics of the nanocomposite and was applied to evaluate the electrical conductivity data obtained for 1% v/v carbon containing CB-PI film. The corrected data show that electrical conductivity in the CB PI nanocomposites is predominantly governed by a nearest neighbour hopping mechanism and the activation energy for the charge carriers was calculated to be about 18.8 meV. The data also fits well to 3D variable range hopping mechanism with a calculated T. value of 16,641 K. (C) 2004 Elsevier B.V. All rights reserved.