Positron Annihilation Study of Polymer Membrane Materials

Abstract

Free volume effects are important for positronium formation, pick-off annihilation and chemical reactions. In order to turn positron annihilation lifetime (PAL) measurements into effective tool for quantitative investigations of molecular solids, polymers for example, the relation between the intensity of the long-lived positronium component of lifetime distribution of positron annihilation and concentration of defects (elementary free volumes EFV) has to be derived. This enables not only calculations of the effective size of elementary free volumes but also estimations of the specific free volume. Meanwhile, the studies of EFV in polymer systems are of great interest, because effective sizes and concentrations of EFV determine many transport, mechanical and other properties of polymers. We demonstrate here an approach to the studies of these problems on example of big group of glassy polymers distinguished by a wide range of gas permeability P (1-10⁴ Barrer) and selectivity. They are used therefore as good gas-separating membrane materials.