Rheological and dielectrical characterization of melt mixed polycarbonate-multiwalled carbon nanotube composites

A series of composites of polycarbonate (PC) with 23 different contents of multiwalled carbon nanotubes (MWNT) was produced by melt mixing using the masterbatch dilution method. In dielectric measurements, AC conductivity and complex permittivity data obtained in the frequency range between 10(-3) and 10(7) Hz at room temperature indicated the electrical percolation threshold at about 1.0 wt%. The dynamic mode melt rheological measurements for the same samples at eight temperatures between 170 and 280 degreesC showed a visible change in the frequency dependence of dynamic moduli and the absolute value of the complex viscosity \eta*\ particularly at low frequencies. In literature these changes are sometimes related to so called 'percolation threshold concentration'. Applying this picture to our experimental data we have to assume that the percolation threshold is strongly dependent on the measurement temperature. It changes from about 5 to 0.5 wt% MWNT by increasing the measurement temperature from 170 to 280degreesC, respectively. This temperature dependence cannot be explained by a classical liquid-solid transition but may be related to the existence of a combined nanotube-polymer network. (C) 2004 Elsevier Ltd. All rights reserved.