Ortho-positronium annihilation parameters in polyvinyl alcohol films with various degrees of polymerization, saponification and crystallinity

摘要

Positron annihilation lifetime (PAL) spectroscopy has been applied to polyvinyl alcohol (PVA) films prepared with commercially available PVA or from polyvinyl acetate (PVAc). The variation of lifetimes of ortho-positronium (o-Ps) formed in the films was investigated as a function of the degrees of polymerization. saponification, or crystallinity. For the fully saponificated samples, no dependence was found to exist on the degrees of polymerization or of crystallinity. For the partially saponificated samples, however. the dependence of the o-Ps lifetime on the degree of saponification was clearly observed, and this is explained by both the formation of hydrogen bonds among the polymer chains and the existence of acetyl group strongly inhibiting the hydrogen-bond formation due to steric hindrance. [References: 12]