The Effects of Water on the Dielectric Properties of Aluminum-Based Nanocomposites

Abstract

A series of polyethylene nanocomposites was prepared utilizing aluminum nitride or alumina nanopowders with comparable morphologies. These were subsequently subjected to different conditioning regimes, namely prolonged storage in vacuum, the ambient laboratory environment or in water. The effect of filler loading and conditioning (i.e., water content) on their morphological and dielectric properties was then examined. Measurements indicated that, in the case of aluminum nitride nanocomposites, none of the conditioning regimes led to significant absorption of water and, as such, neither the dielectric properties nor the DC conductivity varied. Conversely, the alumina nanocomposites were prone to the absorption of an appreciable mass of water, which resulted in them displaying a broad dielectric relaxation, which shifted to higher frequencies, and a higher DC electrical conductivity. We ascribe these different effects to the interfacial surface chemistry present in each system and, in particular, the propensity for hydrogen bonding with water molecules diffusing through the host matrix. Technologically, the use of nanocomposites based upon systems such as aluminum nitride, in place of the commonly used metal oxides (alumina, silica, etc.), eliminates variations in dielectric properties due to absorption of environmental water without resorting to the adoption of techniques such as surface functionalization or calcination in an attempt to render nanoparticle surface chemistry hydrophobic.