Sublinear dispersive conductivity in polymethyl methacrylate at temperatures above the glass transition

Abstract

Dynamic electrical analysis shows that conductivity conditions the electrical properties of a polymer at high temperatures and low frequencies. In this paper we show the possibilities of the electric modulus formalism to study the properties of carrier transport and space charge relaxation processes in polymethyl methacrylate. Asymmetric Argand's plots are observed in the temperature range between 150 and 210°C. This asymmetry is related to power-law dependencies in the real part of the conductivity, of the form ωn with n<1, as a result of correlated ion hopping. The complex part of the electric modulus exhibits a peak in the low frequency range that can be associated with these conductive processes. In the case of the relaxation time related to conductive processes, it has been observed that Maxwell time is higher than the characteristic time associated with the crossover frequency which determines the transition from dc to ac regime. This fact is explained by the presence of deep traps. Finally, a maximum in the value of n is observed between 180 and 190°C which may be related to coupling between charge transport and chain segment motions. © 2004 Elsevier Ltd. All rights reserved.