Effect of epoxy-modified silicone-treated micro-/nano-silicas on the electrical breakdown strength of epoxy/silica composites

The surface of micro-silica and nano-silica was modified with epoxy-modified silicone and their effect on the electrical breakdown strength was evaluated in epoxy/micro-/nano-silica composites (EMNCs). Firstly, the surface of micro- and nano-silica was treated with hydroxyl silane and then the hydroxyl group of the silane was reacted with epoxy-modified silicone. The surface-treated micro- and nano-silicas were mixed with epoxy resin and polyester-modified polydimethylsiloxane (PEM-PDMS) by using an ultrasonicator. Transmission electron microscope (TEM) was used to observe the even dispersion of nano-silica in an epoxy/micro-silica composite and it was found that the nano-silicas were well dispersed. The electrical breakdown strength of the epoxy/micro-silica (60 wt%)/nano-silica (1 phr)/PEM-PDMS (0.5 phr) system was 60.0 kV/2 mm, which was 13.6% higher than that of epoxy/micro-silica (60 wt%)/PEM-PDMS (0.5 phr) system, 52.8 kV/2 mm. The contact angle of neat epoxy was 77°, which was 132% higher than that of epoxy/micro-silica (60 wt%)/nano-silica (1 phr)/PEM-PDMS (0.5 phr) system, 101.6°.