Influence of interface on the electrical properties of polyimide/TiO ₂ 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 TiO₂ in composites contains deep charge traps with density proportional to TiO2 doping 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-TiO₂ doping concentration) and increasing decomposition temperature (T_PI< T_3%<T_7%). When exposed to corona ageing, the PI matrix rather than interface or nano-TiO₂ is initially damaged, and the remaining mixture of interface and nano-TiO₂ are accumulated gradually on the PI/TiO₂ surface forming a "protective" layer which slowing down further PI/TiO₂ erosion in corona ageing.