Effect of ZnO Nanoparticles on the Dielectric/Electrical and Thermal Properties of Epoxy-Based Nanocomposites

The dielectric and thermal response of epoxy resin (ER) based nanocomposites filled with semi-conductive zinc–oxide (ZnO) nanoparticles, were studied in the present work. Dielectric Relaxation Spectroscopy (DRS) technique was used, in the frequency range of 10^–1–10⁷ Hz and temperature range of 30–160 °C, for the investigation of the effect of ZnO nanoparticles on the dynamics of the molecular mobility of ER/ZnO system. On the other hand Differential Scanning Calorimetry (DSC) and Thermogravimetric/Differential Thermal Analysis (TGA/DTA) techniques have been used in order to examine the effect of ZnO nanoinclusions upon the molecular mobility, in relation to the thermal stability of the studied system. Four distinct relaxation mechanisms have been recorded in the spectra of all the systems under study. They were attributed to conductivity relaxation, interfacial polarization (IP), glass to rubber transition of the polymer matrix (α-relaxation) and re-orientation of polar side groups of the main polymer chain (β-relaxation). Dielectric and thermal response could be interpreted by the simultaneous action of two opposite effects: (a) the addition of ZnO nanoparticles leads to a decreasing of the cross-linking density of the epoxy matrix which has as a result an increase of the fractional free volume and of the corresponding molecular mobility, and (b) the strong interactions between filler and epoxy matrix results to a reduction of the mobility of a fraction of the polymer chains at the interfaces of the constituents.