DC and AC conductivity of carbon nanotubes-polyepoxy composites

The dc and ac conductivities of carbon nanotubes-polyepoxy composites have been investigated from 20 to 110 degreesC in the frequency range 10(-2)-10(6) Hz as a function of the conductive weight fraction p ranging from 0.04 to 2.5 wt %. The frequency dependence of the measured conductivity obeys the universal dynamic response (UDR): a dc plateau followed, above a critical frequency w(c), by the w(s) power law with exponent s similar to 0.6-1. The dc conductivity follows a percolation scaling law: sigma(dc) proportional to (P - P-c)(t) with p(c) = 0.3 wt % and t = 1.4-1.8, according to the temperature. sigma(dc) reached 10(-4) S/cm for 2.5 wt % CNTs content and increases with increasing temperature. Considering a biased random walk in three dimensions approach, we may explain the scaling law of w(c) with p and its proportionality to sigma(dc). The universality of ac conduction in carbon nanotubes-polymer composites is examined by the construction of master curves.