INTRODUCTION
Compared with traditional materials, nano materials have a set of special characteristics, such as surface effect, small size effect, quantum size effect, macroscopic quantum tunneling effect and dielectric confinement effect. Attracted by these outstanding characteristics, a large number of researchers in the field of dielectrics and electric insulation have attempted to add nano materials into polymers in order to improve dielectric and insulating characteristics of polymers. It has already been found that nano-sized fillers can improve some key properties of polymers to a certain extent [1].