Dielectric properties of alumina-polymer nanocomposites

We have investigated alumina-LLDPE nanocomposites which have been carefully prepared using melt phase Brabender mixing at 150 °C and extruded using a ram extruder at the same processing temperature with subsequent hot melt pressing of thin polymer films at 150 °C. The dielectric properties of the alumina-LLDPE nanocomposites have been measured from -50 to 70 °C in the frequency range from 10^-2 Hz to 10⁶ Hz. In pure LLDPE, no loss peak can be observed in the observed frequency range. A polyethylene nanocomposite with 1 wt% alumina shows a wide loss peak centered at about 0.06 Hz at -50 °C in the lower frequency domain and this peak remains largely unchanged with increasing temperature. A similar phenomenon is also observed at higher alumina concentrations. Alumina-epoxy resin nanocomposites have also been investigated. In contrast to the LLDPE case, both the interfacial and dipole polarizations can be clearly seen, and their peak positions move to the high frequency region with increasing temperature. The results are discussed in terms of interfacial polarization between the nanoparticles and the polymer matrix.