Study of sorption in poly(vinyl alcohol) using the positron annihilation technique

The vacancy states of fresh and annealed poly(vinyl alcohol) polymers sorbi ng CO2 gas at various pressures have been investigated by the position anni hilation lifetime (PAL) technique. The change of the bulk volume and the am ount of sorbed CO2 gas were measured simultaneously to compare the free vol ume fraction with the size of the ortho-positronium holes. The PAL data ind icate that the size of the ortho-positronium hole increases with the progre ss of the sorption while the sorption and the bulk volume data show that th e free volume fraction becomes constant. Also, it supports the existence of local plasticization and the improvement of the dual mechanism model of so rption of gas.