Transport of helium in polycarbonate membranes

The transport of helium in membranes of poly(bisphenol A carbonate-co-4,4′-(3,3,5-trimethylcyclohexylidene)diphenyl carbonate) (PBCDC) is reported. The experimental values of the diffusion and permeability coefficients, under the upstream pressure of 176 cmHg, are (10.9±0.7)×10−6 cm2 s−1 and 61.4±0.5 barrers, respectively, at 30°C. Both coefficients obey Arrhenius behavior with activation energies of 1.9 and 3.0 kcal mol−1, respectively. The dynamics of helium in the membranes was simulated using the transition state approach (TSA). Very good agreement between the theoretical and experimental values of the diffusion coefficient was found. However, the simulated solubility coefficient is nearly one order of magnitude higher than the experimental value.