Effect of nano-TiO₂ on the polarization process of polyimide/TiO₂composites

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.