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Thermal Expansion of the Free Volume in Poly(vinyl alcohol) Using Positron Annihilation Technique and Group Contribution Method

Positron annihilation lifetime (PAL) as a function of temperatures were measured to determine the thermal expansion coefficient () of the ortho-positronium (o-Ps) hole volume for poly(vinyl alcohol), PVA. On the other hand, the thermal expansion coefficient ( of the bulk volume of PVA has been calculated from measuring the bulk volume as a function of temperature. The group contribution method is used for the calculation of the fractional of the free volume in the glassy and the rubbery states. For the glassy and rubbery states, the ratio of the thermal expansion coefficient of the bulk volume to that of the total free volume is calculated. There is an agreement between these ratios in glassy and rubbery states and those outcomes acquired from the PAL and the substance volume information. This indicated that the o-Ps lifetime is a sign to the free volume in the sample which is also proportional to the total free volume.