In-situ and ex-situ TiO₂-based dielectric polymer nanocomposites

One of the main challenges in understanding the dielectric behavior of nanocomposites is achieving true nanoscale dispersion. In this paper, we introduce in-situ sol-gel synthesis of nanoparticles in the polymer solution as an effective way to overcome dispersion challenges. We compare nanocomposites prepared using commercially available nanoparticles to those prepared using in-situ and ex-situ synthesis of nanoparticles in our laboratory. As-received TiO₂ particles increased the dielectric permittivity of PVDF by 10% at 1kHz but showed strong aggregation and poor dispersion in PVDF. However, in-situ TiO₂/PVDF showed uniform individual dispersion and 96% increase in dielectric permittivity. Nevertheless, the in-situ composite suffered from high dielectric loss, which is likely due to chemical residues left over from the sol-gel process. In order to address this high dielectric loss, TiO₂ particles were synthesized in an ex-situ technique, rinsed and dried to remove the impurities and finally ultrasonicated using a high power probe sonication for 1.5 hr. The ex-situ sample showed 48% increase in dielectric permittivity and reasonably low dielectric loss. There was still some extent of aggregation in the ex-situ sample, which will be addressed using ultra fast centrifugation techniques. The results of our study shed some light on the role of dispersion quality and processing techniques in affecting the final dielectric behavior of TiO₂-based polymer nanocomposites.