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The sorption of organic vapors of different chemical nature, molecular weight and polarity in glassy Matrimid 5218 polyimide films is measured and modeled in the entire activity range up to saturated vapor conditions. Experimental isotherms show several different peculiarities according to the nature of the solute component, consistent with the glassy character of the polymeric matrix. These features range from high vapor solubility coefficient at infinite dilution to swelling and plasticization of the polymer matrix depending on temperature and solute affinity. The various behaviors are then discussed by means of a thermodynamic model for properties of glassy polymeric phases. Indeed, the Non-Equilibrium Lattice Fluid (NELF) model is used to interpret the Vapor-Liquid-Equilibrium below Tg, while the corresponding equilibrium Lattice Fluid model was considered to the same purpose for the case of plasticization conditions in the system. This representation is able to describe consistently all different observed features and allows for a predictive procedure to reproduce solubility isotherms over a wide activity range.

International audience; Considerable interest had been focused during 1950-1980 on the pure gas isothermal sorption diffusion modeling in glassy polymers. In particular, the theory of dual-mode sorption has been developed during this period. It postulates that two concurrent sorption modes occur in the microheterogeneous medium. On the basis of this theory, rather complete and successful models have been roposed. In this paper, a short review of dual-mode-sorption models is first given. By considering a general expression of the sorption mode, the conventional models (partial immobilization model and immobilization model) become one limit-behavior model: the time-lag upper-bound model. Another limit-behavior model, the time-lag lower-bound model called the dual-diffusion model, is particularly investigated and compared to conventional models in this paper. It is shown that the steady-state permeability is independent of the molecule exchange rate, while the time-lag prediction depends on it. Furthermore, the time-lag lower-bound model provides, in general, a better agreement with experiments. In this respect, the dual-diffusion model is considered as a simple and efficient dual-mode-sorption theory approach.

An analysis of the empirical correlations that relate the solubility coefficient of gases at infinite dilution in glassy polymers to penetrant properties has been performed, by considering gas sorption as a succession of three steps: condensation of the penetrant, dissolution in the equilibrium polymeric phase, and departure of the system from equilibrium. The infinite dilution solubility coefficient is obtained from the contributions of the three steps, the first two of which involve standard equilibrium thermodynamics, while the latter requires nonequilibrium considerations and is described by using the nonequilibrium lattice fluid (NELF) model. The various terms have been evaluated for several gases in polycarbonate, polysulfone, poly(phenylene oxide), and poly(methyl methacrylate). It has been found that the largest term in the expression of solubility is due to condensation, which explains the observed correlation between solubility and critical temperature, while the out of equilibrium contribution to solubility, which generally gives numerical values lower than the condensation term, is in turn more strongly correlated to the penetrant critical volume.