Maxwell-Wagner-Sillars interfacial polarization in dielectric spectra of composite materials: Scaling laws and applications

Abstract

An experimental and theoretical investigation of the scaling laws governing the phenomenon of Maxwell-Wagner-Sillars interfacial polarization in composite materials in dependence on morphology, volume fraction, orientation of fillers, form factor and the presence of interphases is presented in the current study. By considering the complex dielectric function of the matrix and of the fillers, the dielectric spectra are calculated in the frequency range from 10⁷ Hz to 10^-2 Hz and compared to dielectric measurements by Broadband Dielectric Spectroscopy, carried out in the frequency range from 10⁷ Hz to 0.5Hz and between -90^oC and 150^oC. The characteristic frequencies of the global dielectric response are reported to strongly vary with the conductivity value of the conductive phase, while a much weaker dependence is observed upon varying the volume fraction, the form factor and the orientation of fillers. The value of permittivity at low frequency does not change with the conductivity value, whereas a significant variation is observed in dependence on the composite morphology, form factor, orientation of fillers and presence of interfaces with different gradients of properties. Two possible applications of our analysis are reported: (i) measuring the conductivity of materials without employing a direct electrical contact between the electrodes and the sample and (ii) discriminating different phenomena of electrical polarization in complex materials by analyzing the scaling laws. Our study delivers thus a useful and necessary analysis of the dielectric behavior of composite materials, where interfacial polarization effects play a major role.