Effects of nanofiller materials on the dielectric properties of epoxy nanocomposites

Effects of nanofiller materials on typical dielectric properties of bisphenol-A epoxy resin were compared among three kinds of nanofillers, i. e. boehmite alumina, titania, and silica. In all the samples, the complex permittivity ε_r' and ε_r become significantly higher with an increase in temperature beyond 120 °C, especially at low frequencies. Such increase iinε_r' and ε_r indicates the abundance of mobile charge carriers, which was verified by the space charge distribution measurements. All the samples show two peaks at 110 and 180 °C in the thermally stimulated depolarization current spectra. The lower-temperature peak is apparently caused by depolarization of dipoles induced by the glass transition, while the higher-temperature peak is due to the release of space charge. These characteristic properties appear more significantly in the nanocomposites with boehmite alumina and titania and less significantly in the nanocomposite with silica than in the neat epoxy esin. This indicates that the silica nanofillers give the best results as far as these properties cconcerned. The suppression of molecular motion by the addition of nanofillers seems to work effectively in the case of silica, while the nanofiller addition is likely to aaccelerate the motion of ionic carriers and/or that of dipoles in the case of boehmite alumina and titania.