Iodine-doped polyvinylalcohol using positron annihilation spectroscopy

Iodine-doped polyvinylalcohol, doped up to 52 wt %, was studied using positron annihilation lifetime technique and Doppler broadening of annihilation radiation. Three component, free fit analysis was used for the lifetime spectra. It is found that $I_3$ drops sharply on initial iodine doping, whereas decrease in ${\tau }_3$ is small, indicating inhibition of positronium formation by the dopant. The S parameter, on iodine doping, initially shows a drastic increase due to the decrease in crystallinity of the doped sample. Differential scanning calorimetry (DSC) and x-ray diffraction curves confirm that doping results in decreased crystallinity of the sample. ${\tau }_3$ increases beyond 23 wt % doping level due to structural changes induced by formation of polyiodide complexes, which is confirmed by UV-Vis spectra, for moderately and highly doped samples. The drop in ${\tau }_3$ at higher levels of doping (>44 wt %) suggests chemical quenching of positronium, probably due to iodine aggregation. DSC confirms formation of iodine aggregates, as revealed by a large endotherm at $185°\mathrm{C},$ for doping levels beyond 47 wt %.