Optical, Dielectric Properties and Energy Storage Efficiency of ZnO/Epoxy Nanocomposites

Abstract

ZnO/epoxy nanocomposites were prepared in five different contents (0.25–3.0 wt%). Optical, thermal and dielectric properties have been examined as a function of ZnO nanoparticles. The absorption optical spectra exhibit a broad intense peak assigned to the n–π* (HOMO–LUMO) transitions. Nanocomposite with 3.0 wt% ZnO sample completely blocks UV-light radiations in the region from 300 to 480 nm, which allowed that the prepared material to be used for UV-Shielding devices. The optical band gap is found to decrease with increasing filler ZnO concentrations. This might be due to increasing the density of defect states. Permittivity and electric modulus formalisms are used to analyze and interpret the experimental data. γ relaxation is observed in the low temperature region, which is attributed to the rearrangement of small parts of the polymeric chains. The α relaxation and the Maxwell–Wagner–Sillars (MWS) effect, attributed to the glass rubber transition of the polymeric matrix and the interfacial polarization phenomena respectively, are observed in the high temperature region. Using Havriliak–Negami approach, the temperature dependence of relaxation time for MWS and γ relaxations follows an Arrhenius behavior while the α relaxation time is well described by the Vogel–Fulcher–Tamann behavior. The activation energies of all relaxation modes were calculated and discussed. The energy density of the investigated samples is significantly enhanced. It is about 2 × 10−6 J/m3 for nanocomposite with 3.0 wt% ZnO at 20 °C. These results indicate that the effect of ZnO nanoparticles makes the proposed materials suitable candidates for energy storage applications.