The result above is also an outcome of the Freeman's theory if one assumes d CO2 = d N2 . If the Eq. 3 were true, it would give us a useful insight on the limiting behavior of the polymer materials. For example, in the limiting case of infinite dilution, the solubility (S 0 ) is dominated by the gas condensability, usually associated with its critical temperature (T C ), and the sorption selectivity can then be expressed as: