Dielectric Properties of Epoxy-Alumina Nanocomposites: The Effect of Absorbed Water

In previous reported work we found an unusual dielectric behavior for alumina filled nanocomposites which relates to very different dynamics for adsorbed water in the materials. This was shown to depend on the polarity of the polymer matrix. In some cases, the dielectric loss peak observed in the low frequency region shifted to lower frequency with increasing temperature. This is opposite to common observed behaviour of this type of dielectric loss peak in dielectrics which generally shows a thermally activated response. In this paper we report an investigation into the dielectric responses in the frequency domain from 10^-2 Hz to 10⁶ Hz at the temperature range from -50 to 120 degC of nano-alumina filled epoxy composites. The dielectric behavior has been investigated both before and after an exhaustive drying treatment of both the nanocomposite dielectric as well as the free nano-alumina powder prior to incorporation in the matrices. The results show that the unusual dielectric behavior is only observed for both nanocomposites and nano-alumina powder before the drying treatment. After drying no unusual dielectric response is observed. This suggests that the unusual behavior is related to the location and mobility of water in materials which support a very high internal surface area.