Effect of Interphase on Dielectric Relaxation Mechanisms in Epoxy-Alumina Nanocomposite

The interphase formed between polymer and a nanoparticle plays a critical role in the dielectric properties of the nanocomposite material. The effect of interphase on dielectric relaxation mechanisms is analyzed in this work. Unfilled epoxy and epoxy-alumina nanocomposite samples with 0.l, 1 and 5 wt% filler loadings are prepared. SEM analysis is conducted to ensure dispersion of nanoparticles. Impedance and permittivity measurements are taken over the frequency range of 10 mHz-10 MHz. Equivalent circuit models are derived from impedance spectroscopy measurements for unfilled and nanofilled samples. A method based on genetic algorithm is used to optimize the equivalent circuit parameters. Initialization of parameters for the algorithm is selected based on the shape of Cole-Cole plot. The proposed equivalent circuit models based on relaxation time constants indicate the presence of polarization at the interphase region in nanocomposite. Variations in configuration and parameters of equivalent circuit for unfilled and filled epoxy are used to analyze the effect of interfacial polarization. Polarization at the interphase is differentiated from other relaxation mechanisms at 0.1 and 1 wt% based on equivalent circuit model. At 5 wt%, the optimized equivalent circuit configuration and corresponding relaxation time constants different from circuit models for other filler loadings is attributed to the presence of overlapping of interphases.