Influence of nanopores on molecular polarizability and polarization currents in epoxy nanocomposites

Epoxy resin based nanocomposites with silica (SiO₂), alumina (Al₂O₃) and zinc oxide (ZnO) as nano fillers were fabricated to investigate the relationship between the polarization and depolarization current. The polarization and depolarization current, charge carrier mobility, absorption current and nano size free volume cavities of nano dielectric epoxy composites and their interrelation are discussed. It is observed that the current magnitude increases in the three nanocomposites with loading of nano SiO₂, Al₂O₃ and ZnO and the peak width of each composite is greater than that of pure epoxy. Free volume studies are carried out using positron annihilation lifetime spectroscopy (PALS). From the results it is observed that molecular polarizability decreases and charge carrier mobility increases with the incorporation of SiO₂, Al₂O₃ and ZnO loading. This trend is typical in Al₂O₃, whereas in case of SiO₂ the molecular polarizability is unaffected and with ZnO, molecular polarizability and charge carrier mobility decrease above 10 wt% filler. The Al₂O₃ nanofillers are structurally different as compared to SiO₂ and ZnO fillers. It is observed that Al₂O₃ has more influence on polarizability of the composite.