Dielectric relaxation processes in epoxy resim-ZnO composites

Abstract

Polymer matrix-ZnO microcomposites were prepared in different filler concentrations. The electrical relaxation dynamics of all samples was examined by means of broadband dielectric spectroscopy (BBS) over a wide temperature range. Two relaxation modes (namely ß and y), observed in the low temperature region, are attributed to the reorientation of small polar groups of the polymer matrix. Glass-rubber transition (α-mode) of the polymeric matrix and interfaeial polarization phenomena are considered as responsible for the recorded relaxation processes in the high temperature region. An additional relaxation mode, named intermediate dipolar effect (IDE), is recorded at temperatures higher than -30 °C in all composites. Its occurrence and dynamics are related to the presence and concentration of the filler. IDE and α-relaxation are observed in the same frequency and temperature range, leading to a mutual superposition. The two processes were distinguished following a simulation procedure employing the simultaneous fitting of two Havrilliak-Negami terms and a third term describing the contribution of DC conductivity to dielectric losses. The temperature dependence of relaxation times for α-mode follows the Vogel-Tamann-Fulcher equation, whereas IDE relaxation times follow unusual temperature dependence. The latter is discussed under the assumption of intrinsic interfacial polarization phenomena within ZnO crystal domains. © 2009 Wiley Periodicals, Inc.