Free-volume hole properties (free-volume size, fraction, and distribution) of polycarbonate (PC) exposed to CO 2 and N 2 gases are investigated using positron annihilation lifetime (PAL) spectroscopy. In PC/CO 2 systems, free-volume hole size and fraction significantly increase as a function of CO 2 pressure in the range 0−1000 psi. Hysteresis is observed during CO 2 sorption/desorption. In PC/N 2 systems, free-volume hole size and fraction reach maxima at a pressure of about 800 psi but no hysteresis is observed. Free-volume hole distribution in the CO 2 -exposed polymers is found to be significantly broader than in unexposed samples. The observed variation in free-volume properties of PC exposed to gas is discussed in terms of penetrant plasticization, gas hydrostatic pressure effect, and molecular filling and creation of holes in the polymer matrix.
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Hong et al. (1996) studied this question.
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