Positron annihilation spectroscopy and mechanical properties studies for epoxy matrices reinforced with different nanoparticles

In this study, polymeric nanocomposites was composed of an epoxy polymer matrix reinforced with metal oxides Alumina (Al2O3), Silica (SiO2), and Carbon black (C) nanoparticles. Three different weight concentrations (0.5 wt%, 1.5 wt% and 3 wt%) of each nanofiller were dispersed in epoxy resin with sonication. Hardness and tensile properties for different contents were investigated. The effect of alumina, silica, and carbon nanoparticles on the nano-scale free volume properties of epoxy matrices was studied using positron annihilation lifetime spectroscopy (PALS). The S parameter was also measured for all samples as a function of the weight fractions of nanofiller. The behavior of the S parameter was analyzed in terms of positron annihilation and positronium formation. Dispersion and distribution of nanoparticles in epoxy was studied by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). The results showed that the minor addition of nanoparticles to epoxy resin increases the hardness. In addition, for 3 wt% the tensile strength was reduced for all composites over neat epoxy. Furthermore, the PLAS results indicated that the mechanical properties such as hardness, tensile strength and tensile modulus have a significant dependence on free volume. Attempts were made to correlate the available free volume with mechanical properties, which leads to general belief that any process reduces the free volume increases of both hardness and tensile strength.