Influence of interface on the electrical properties of polyimide/TiO₂ composite films

Polyimide/TiO2(PI/TiO2) composite films were fabricated by in-situ polymerization and are reported in this paper. The effect of interface (PI-TiO2) on dielectric and breakdown properties was investigated via conductivity, photo-stimulated discharge (PSD), permittivity, thermo-gravimetric analysis (TGA) and breakdown characteristic. The results show that interface between PI and TiO2in composites contains deep charge traps with density proportional to TiO2doping concentration. Interface enhances space-charge polarization to increase conductivity and loss tangent at low frequency. The pinning influence of interface on PI molecular chain motion is reflected in the downtrend of permittivity (0%-4% nano-TiO2doping concentration) and increasing decomposition temperature (TPI3%7%). When exposed to corona ageing, the PI matrix rather than interface or nano-TiO2is initially damaged, and the remaining mixture of interface and nano-TiO2are accumulated gradually on the PI/TiO2surface forming a “protective” layer which slowing down further PI/TiO2erosion in corona ageing.