Influence of nanopore size on particle porosity and permittivity of nanoporous-silica/epoxy composite

To achieve a lower permittivity solid insulator for HV power apparatus, we have developed a polymer composite filled with nanoporous silica particles. This paper investigated the influence of nanopore size of the nanoporous-silica particles on particle porosity and permittivity of nanoporous-silica/epoxy composite (NanoPC). NanoPC was prepared by mixing epoxy resin and four kinds of nanoporous-silica particles which had different average pore sizes in the range of 0.6 - 15 nm. The particle porosity of NanoPC, which was defined as the ratio of particle pore volume to a particle volume, was evaluated from the specific gravity measurements. From the electrical capacitance measurement of the NanoPC, the relative permittivity was obtained. As a result, NanoPCs whose average pore size were less than 3 nm had large particle porosity larger than 20 vol%. The permittivity of NanoPCs whose average pore size was 3 nm was found to be lower than that of unfilled epoxy resin.