AC-impedance and dielectric properties of hybrid polymer composites

The AC-impedance and dielectric properties of hybrid polymer composites made up of epoxy (diglycidyl ether of bisphenol-A) matrix filled with various zinc oxide concentrations (0, 4.9, 9.9, 14.9 and 19.9wt%) and reinforced with conductive carbon black nanoparticles (0.1wt%) have been investigated as a function of fillers concentrations, applied frequency in the range from 20kHz to1MHz and temperature in the range from 30? to 110?. The observed data were analyzed using the dielectric permittivity and electric modulus formalisms (i.e. the inverse quantity of complex permittivity). The dielectric constant of the composites increases with increasing temperature and filler concentrations, and this case can be explained by hopping and tunneling processes. The AC-conductivity is apparently enhanced with increasing frequency, temperature, zinc oxide and carbon black fillers. The observed increase in the AC conductivity was explained based on the concept of conductive paths and connections between the zinc oxide-particles and the conductive carbon black-nanoparticles. The activation energy has been estimated from fitting the AC conductivity-temperature data and it was found that it is decreased by the addition of the zinc oxide content in the epoxy matrix reinforced with carbon black, which means that the composites have better electrical conduction. The scanning electron microscopy images revealed that the dispersed zinc oxide-particles and carbon black-nanoparticles were randomly distributed within the epoxy matrix with some paths and surface contacts between the fillings. It was found that the addition of carbon black nanoparticles to epoxy/zinc oxide composites enhances the electrical conduction due to the electronic and impurity contributions.