PRESSURE-DEPENDENCE OF FREE-VOLUME HOLE PROPERTIES IN AN EPOXY POLYMER

Positron annihilation spectroscopy has been applied to study free-volume properties in an amine-cured epoxy as a function of quasi-isotropic pressure in the range 0-15 kbar. The orthopositronium lifetimes are found to decrease largely as a function of the increase of pressure while the corresponding intensities decrease slightly. The positron lifetime-pressure variation is found to be similar to that of orthopositronium. This pressure variation provides evidence that both the positronium atom and the positron are localized at free-volume holes in polymers. The pressure variations are found to be significantly different from that previously measured under uniaxial pressure. The properties of free volume, mean hole size, fractional free-volume hole content, and free-volume compressibility in the epoxy polymer are obtained from the lifetime results.