Electric modulus and interfacial polarization in composite polymeric systems

The applicability of the electric modulus formalism is investigated on a Debye-type relaxation process, the interfacial polarization or Maxwell-Wagner-Sillars effect. Electric modulus, which has been proposed for the description of systems with ionic conductivity and related relaxation processes, presents advantages in comparison to the classical approach of the real and imaginary part of dielectric permittivity. In composite polymeric materials, relaxation phenomena in the low-frequency region are attributed to the heterogeneity of the systems. For the investigation of these processes through electric modulus formalism, hybrid composite systems consisting of epoxy resin-metal powder-aramid fibres were prepared with various filler contents and their dielectric spectra were recorded in the frequency range 10 Hz-10 MHz in the temperature interval 30-150 degrees C. The Debye, Cole-Cole, Davidson-Cole and Havriliak-Negami equations of dielectric relaxation are expressed in the electric modulus form. Correlation between experimental data and the various expressions produced, shows that interfacial polarization in the systems examined is, mostly, better described by the Davidson-Cole approach and only in the system with the higher heterogeneity must the Havriliak-Negami approach be used. (C) 1998 Chapman and Hall.