Ionic conductivity and free volume related microstructural properties of LiClO4/PVA/NaAlg polymer composites: Positron annihilation spectroscopic studies

Poly(vinyl alcohol) (PVA)/sodium alginate (NaAlg) polymer composites were prepared by doping with lithium perchlorate salt (LiClO4) using solution casting method. The miscibility, crystallinity, conductivity, thermal behavior, mechanical strength and free volume properties have been examined. The FTIR results reveal that the dopant (Li+) ions interact strongly with polymer chains through hydrogen bonding. X-ray diffraction patterns show a variation in the degree of crystallinity with increase in LiClO4 concentration. The dc conductivity increases with addition of LiClO4 salt concentration at room temperature and is attributed to increase in the number of mobile charge carriers (Li+ and ClO4−) and degree of dissociation of salt in the composites. The variations in the mechanical properties are observed upon doping. The differential scanning calorimetric (DSC) study shows a single glass transition temperature (Tg) and reveals the compatibility and variation in the decomposition temperature (Td). Thermogravimetric analyses (TGA) shows a decrease in the decomposition temperature with addition of lithium salt concentration. The positron annihilation lifetime spectroscopy (PALS) and Doppler broadening measurements were carried out for all the samples in terms of positron annihilation and positronium formation. The S-parameter shows a similar behavior as that of the o-Ps lifetime and o-Ps intensity. The correlation between carrier concentration and ionic conductivity with Ps formation was observed in this particular system. The conductivity versus temperature plot was found to follow an Arrhenius nature.