Dielectric Properties of Composites of Polypropylene with Zno-TiO2 Core-Shell Nanoparticles

Composites of polypropylene with different weight percentages of ZnO-TiO₂ core-shell nanoparticles were prepared by the combination of solution and mixture melting methods. Dielectric properties of polypropylene composite films were studied at frequencies ranging from 50 Hz to 5 MHz at four different temperatures (313, 333, 353, and 373 K). It is observed that the dielectric constant reduces quickly in the low-frequency range followed by a near frequency independent behavior above 1 KHz. The dielectric properties of composites at low frequency can be explained by interfacial polarization or Maxwell-Wagner-Sillars effect. It is also observed that the dielectric constant reaches the maximum value at 3 wt% of ZnO-TiO₂, which is the percolation threshold of nanocomposite. As the weight percentage of ZnO-TiO₂ increases beyond the percolation threshold up to 7%, the dielectric constant of the nanocomposites decreases. The dielectric loss of the composites follows the similar trend with frequency as the dielectric constant. A sharp increase in the dielectric loss of the nanocomposite observed near the percolation threshold is due to leakage current produced by the formation of conductive network by ZnO-TiO₂ core-shell nanoparticles. Further, peaks in the loss tangent observed for the nanocomposite systems indicating the appearance of a relaxation process. These relaxations peaks were shifted to higher frequencies as the particle content increased, since relaxation processes were influenced by the interfacial polarization effect which generated electric charge accumulation around the ZnO-TiO₂ core-shell nanoparticles.