Iodine-doped polyvinylalcohol using positron annihilation spectroscopy

Iodine-doped polyvinylalcohol, doped up to 52 wt %, was studied using posit ron annihilation lifetime technique and Doppler broadening of annihilation radiation. Three component, free fit analysis was used for the lifetime spe ctra. 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 drasti c increase due to the decrease in crystallinity of the doped sample. Differ ential 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 o f polyiodide complexes, which is confirmed by UV-Vis spectra, for moderatel y and highly doped samples. The drop in tau(3) at higher levels of doping ( >44 wt %) suggests chemical quenching of positronium, probably due to iodin e aggregation. DSC confirms formation of iodine aggregates, as revealed by a large endotherm at 185 degrees C, for doping levels beyond 47 wt %. [S016 3-1829(99)08321-6].