HIGH-SENSITIVITY OF POSITRON-ANNIHILATION LIFETIME TO TIME AND PRESSURE EFFECTS IN GAS-EXPOSED POLYMERS

Positron annihilation lifetime (PAL) experiments are performed in poly carbonate (PC) exposed to CO2 and He gases as a function of time and p ressure. In PC/CO2 systems, hole size and fraction reduced from PAL da ta increase as a function of CO2 pressure and exposure time. Significa nt hysteresis in positron lifetime data is observed during CO2 abasorp tion/desorption. In PC/He systems, no variation is observed. Hole size distribution in the CO2-exposed polymers is found to be significantly broader than in unexposed samples. ?he high sensitivity of PAL result s to CO2 exposure of PC is thought to relate to the microstructural ch anges in the polymer matrix, such as penetrant plasticization, gas hyd rostatic pressure effect, and molecular filling and creation of holes.