Dielectric Integrity of High-Temperature Nanocomposites

The addition of nanoscale metal oxide fillers to polymers has been shown, in many cases, to lead to an improvement in the dielectric breakdown strength and voltage endurance. In this paper, dielectric properties for silica- and alumina-filled polyamideimide (PAI) thin films are reported as a function of particle loading. The dispersion and thermal behavior are quantified. Experiments were also conducted using particulates which were functionalized with Aminopropyltriethoxysilane in order to augment the chemical bonding to the host matrix. The glass transition temperature and decomposition temperature are reported as a function of nanoparticle type and loading. The dielectric strength is provided for both AC and DC voltages. It was found that the enhancement in breakdown strength for a nanocomposite formulation is greater under DC conditions than AC. In addition, alumina filled PAI was found to exhibit greater electrical breakdown strength than silica filled PAI. A discussion of possible reasons is included.