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The dc and ac conductivities of carbon nanotubes−polyepoxy composites have been investigated from 20 to 110 °C in the frequency range 10-2−106 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 ωc, by the ωs power law with exponent s ∼ 0.6−1. The dc conductivity follows a percolation scaling law: σdc ∝ (p − pc)t with pc = 0.3 wt % and t = 1.4−1.8, according to the temperature. σdc 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 ωc with p and its proportionality to σdc. The universality of ac conduction in carbon nanotubes−polymer composites is examined by the construction of master curves.
Barrau et al. (2003) studied this question.