Effect of nano-TiO2 on the polarization process of polyimide/TiO2 composites

Polyimide/TiO2 composite films have been successfully prepared by in-situ dispersive polymerization. The cross section surface morphology, film composition, electrical conductivity and dielectric properties of the composite films are characterized. The results show that inorganic TiO2 nanoparticles are well dispersed in the polymer matrices. We observed that polyimide/TiO2 composites exhibit lower relative permittivity at low TiO2 doping concentration (0–3%) compared to a pure polyimide; and exhibit higher relative permittivity at higher TiO2 doping concentrations (>5%); dielectric loss (loss tangent) is enhanced at frequencies <10 Hz and reduced at frequencies >104 Hz as TiO2 doping concentration increases. TiO2 nanoparticle doping brings space-charge polarization to composite matrices through enhanced charged carrier generation. At the same time, TiO2 nanoparticle doping sites act as pinning mechanism to reduce polymer chain motion in orientation polarization. The interplay of these two polarization processes determines the dielectric property changes that we observed on polyimide/TiO2 composites.