Breakdown, free-volume and dielectric behavior of the nanodielectric coatings based on epoxy/metal oxides

Abstract

In this work electrical properties of an epoxy resin (DGEBA/OTBG) reinforced with alumina (10 nm) or zinc oxide (100 nm) were studied. The dielectric breakdown, relative permittivity, conductivity and dielectric loss were measured in five different nanocomposites for each nanoparticle varying temperature whenever possible. An increase of 50 % of the dielectric breakdown at room temperature in nanocomposites reinforced with only 0.4 % of as-received alumina nanoparticles was obtained. Aiming to understand a relation between state of dispersion of nanofillers and some properties a filler dispersion index Nearest Neighbor Distance was calculated based on FIB/FESEM images of the nanocomposites. This index is related to the dispersion of breakdown probability data and to the best of our knowledge it is not discussed in any other work in the literature. Dielectric spectra provided evidences of the decrease of mobility of charge carriers in lower filler loading nanocomposites due to trapping of charge carriers at the interphase. The percolation threshold of the interphase was reached at higher filler loading nanocomposites than 6 % phr, where the charge carriers have more mobility leading to paths of conductivity. These results corroborates with the drop observed in the dielectric breakdown for percolated nanocomposites. Another important issue found in this work, is that there was no change in the free-volume of the nanocomposites compared to neat epoxy. It is possible to state that in our system free-volume can not explain the variation on dielectric behavior as pointed out in the literature.