Some mechanistic understanding of the impulse strength of nanocomposites

Improvements in the dielectric properties of composite dielectrics have been previously documented when the filler material used is reduced to nanometric dimensions. While the reasons for this have been traced to the physics and chemistry taking place at the interface, and dramatic changes in the magnitude and dynamics of the internal charge are also known to occur, a clear picture of the exact mechanisms taking place has not emerged. This contribution seeks to compare the direct voltage breakdown of composites formed from biphenyl epoxy resin and titanium dioxide in both nanometric and conventional micron-scale forms with that obtained under impulse voltage conditions. The same materials are subjected to an internal charge analysis using the pulsed electroacoustic technique which shows that, in the case of the nanomaterials, a marked homocharge is formed in front of the cathode which would suggest that the dramatic improvements in voltage endurance seen for these materials may be due to the shielding effect of this negative charge. The finding also suggests that the negative charge is formed as the result of scattering occurring in the nanodielectric which is not present to the same extent in the conventional counterpart.