Impact of electron-beam irradiation on free-volume related microstructural properties of PVA:NaBr polymer composites

Sodium Bromide doped Poly(vinyl alcohol) (PVA:NaBr, 80:20) polymer composite films were prepared using a solution casting method. These films were subjected to 8 MeV electron beam radiation at a dose of up to 300 kGy in air at room temperature. The free volume related microstructural and electrical properties of these irradiated films were studied using various characterization methods, such as positron annihilation lifetime spectroscopy (PALS) and AC and DC conductivity measurement techniques. The variations in the positron lifetime data indicate that the free-volume related properties of the doped polymer are affected by irradiation. From the results, it is found that at lower doses, a cross-linking network provides hopping sites for Na⁺ ions, and at higher doses, the chain-scission process facilitates ionic transport through segmental motion. Thus, the free volume around the polymer chain leads to mobility of the ions as well as the polymer segments and hence contributes to the enhancement of conductivity