Study of the interfacial MWS relaxation by dielectric spectroscopy in unidirectional PZT fibres/epoxy resin composites

Polymer composites made of an epoxy resin matrix with oriented PZT fibres in various amounts were prepared and their dielectrical spectra were determined in the frequency range 0.1 Hz-100kHz and a temperature interval from the ambient to 170 degrees C. For the epoxy resin, two relaxation processes were identified. The first is attributed to the glass transition and appeared in the frequency range 1-10(3) Hz. This mechanism is the dominant one. The second phenomenon is related to the dc conduction and is noticeable only at low frequencies/high temperatures domain. For the piezocomposites, an interfacial polarization or Maxwell-Wagner-Sillars (MWS) relaxation process were identified for temperatures above the glass transition. This MWS polarization is hidden by the high values of epsilon' and epsilon, for that the measured data was analyzed using the electric modulus formalism, which presents advantages in comparison to the classical approach of the real and imaginary parts of dielectric permittivity. Using the normalized curves representation, data give evidence to the so called beta* relaxation for all studied samples at the high-frequency range. (c) 2006 Elsevier B.V. All rights reserved.