Influence of grafting modification on dielectric properties of epoxy-grafted SiO2/Epoxy composites

In order to study the effects of grafting modification on the dispersion and dielectric properties of SiO₂/epoxy nanocomposites, in toluene solvent, epoxy molecules were grafted to the silane coupling agent (KH550) which were pre-grafted on the surface of nano-SiO₂ fillers previously. Original SiO₂ fillers and epoxy-grafted SiO₂ fillers were used for preparing two kinds of SiO₂/epoxy nanocomposites by solution blended process respectively. Results of Fourier Transform Infrared spectrometer (FT-IR), thermogravimetric analyzer (TGA) and transmission electron microscopy (TEM) show that epoxy molecules were grafted on the surfaces of SiO₂ fillers successfully by KH550, and the grafted SiO₂ fillers have better dispersion in organic phase. Broadband dielectric spectroscopy and electrical breakdown tester were performed to measure the complex permittivity and AC breakdown strength of composites. Compared with neat epoxy, the addition of grafted SiO₂ fillers improves the breakdown strength and makes lower dielectric constant at low temperature and high frequency, while the addition of original SiO₂ fillers makes bigger dielectric constant and dielectric loss than neat epoxy and grafted SiO₂/epoxy nanocomposite especially at high temperature and low frequency. The grafted SiO₂ fillers are helpful to build better interfaces between fillers and resin matrix and to accelerate the cross-linking reaction, but meanwhile introduce new branched segments to the resin matrix.