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

Abstract

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 orthopositronium (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.

Microstructural evaluation of poly(vinyl alcohol)‐based hydrogels obtained by freezing‐thawing technique: Thermal analysis and positron annihilation

“…Cowie et al20 have shown the effect of hydrogen bonding on the free volume in polymer blends based in poly( N ‐vinylpyrrolidone) and poly(vinyl acetate‐ co ‐vinyl alcohol), revealing an increase of the free volume with the increase of hydrogen bonding, specially caused due to hydroxyl and carbonyl groups. Muramatsu et al21 have founded that for fully saponificated PVA samples, regardless of degree of polymerization, τ 3 was found to be independent on the degree of crystallinity. We suggest that the hydrogen bonding is the driving force for the crystalline disorder in PVA/PES hydrogels, mainly caused due carbonyl and sulfonated groups of PES and the hydroxyl groups of PVA.…”

Novel quaternized polyvinyl alcohol/quaternized chitosan nano-composite as an effective hydroxide-conducting electrolyte

“…The crystallinity was estimated to be 9.8% for the cross-linked Q- [49,51,52]. The lifetime and intensity data depend on the degrees of hydrolysis, crystallinity, cross-linking density, and degree of polymerization [53]. The mean free-volume radius in the pristine Q-PVA was calculated to be 3.08 Å, and for the Q-PVA/5% Q-chitosan, the value was 2.73 Å.…”

Structural Insight into Chitosan Supports Functionalized with Nanoparticles

“…Using a low-energy positron beam, free volume size and free volume concentration can be measured from the Ps lifetime and intensity data [13,14]. Usually, the third lifetime component (τ 3 ) is associated with the means radius of the free volume sites, and the intensity I 3 is related to the concentration of the free volume sites.…”