Comparative Effect of Gamma Irradiation on the Nano-Free Volume and Electrical Properties of PVA/PEG/Reduced Graphene Oxide Nanocomposites

Reduced graphene oxide (RGO) doped polyvinyl alcohol/ polyethylene glycol (PVA/PEG) films were prepared by solution casting technique and exposed to 100 gamma radiation. The structural modifications in the samples before and after irradiation were studied using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry DSC. The free volume holes V-f determined from the ortho-positronium (o-Ps) lifetime (tau(3)) measured by the positron annihilation spectroscopy (PALS) is found to decrease from (84.52 to 67.24 angstrom(3)) and from (85.67 to 78.21 angstrom(3)) for nonirradiated and irradiated samples respectively with increasing the nanoscale RGO filler content into the polymer matrix. The resulting decrease of the free volume holes size due to this incorporation could be explained by both the formation of hydrogen-bonding and crosslinking between RGO and PVA/PEG blend as confirmed by XRD and FTIR measurements. This also caused a decrease in the concentration of free volumes F-r for both nonirradiated and irradiated samples. The increased D.C. electrical conductivity with increasing RGO volume fraction (0-0.265) suggests a conductivity chain formation through the nanoparticle aggregation. The deduced Ln sigma is found to be positively correlated with the probability of free annihilation of positrons I-2 trapped at crystalline-amorphous interfaces. The D.C. conductivity results could be successfully fitted using the model suggested by Miyamoto and Shibayama. The critical free volumes for the charge carriers transport has been deduced to be 80.34 and 82.16 angstrom(3) for nonirradiated and irradiated samples respectively.