The Dielectric Response of Polar and Non-Polar Nanodielectrics

In order to understand the relationship between the dielectric properties and the structure of polymer nanocomposites, especially the role of the interface on dielectric response, two polymers with different polarity were used to form nanocomposites with nanoalumina powder, a typical polar inorganic compound. Consequently, two kinds of nanodielectrics with very different interfaces were produced. In the epoxy nanodielectric, broad band dielectric spectroscopic measurements show that no difference is found between the unfilled resin and the nanocomposite under dry conditions. However, their dielectric responses are very different when they contain about 0.4 % b.w. absorbed water, a concentration that occurs under ambient exposure conditions. The findings suggest that the sites for absorbed water in the epoxy nanocomposites are very different to those in the unfilled thermoset and relate to the large interfacial internal surface in these materials. In this case all the relaxation processes can be well described by the Havriliak-Negami function, which give useful information on the dynamics and activation energies associated with the relaxation processes. In polyethylene nanocomposites, dielectric measurements show that the incorporation of nanoalumina produces a dielectric loss peak in the low frequency. This relaxation peak moves to high frequency with increasing nanoalumina content and the peak becomes broader. In the presence of 0.06 % b.w. absorbed water this peak also shows the same type of unusual dielectric loss behavior as that observed in the undried epoxy nanodielectrics. This behavior is thought to arise from the interplay between interfacial water mobility and bonding rather than the host polymer.