Modeling gas solubility in glassy polymers

Solubility of gas or vapor components in glassy polymers is relevant in numerous processes and applications, such as the development of gas separation membranes or gas barrier materials for packaging, analysis of gas sensors, piping of gaseous streams and many more. Modeling tools for the prediction of gas solubility in glassy polymers would be indeed of great help to the evaluation of performances of different materials in above mentioned applications. It would allow for a much more efficient selection procedure with respect to the direct experimental analysis which, in turn, would be not attainable at all for the case of complex gaseous mixture with variable temperature, pressure and gas composition. In fact, different from the case of rubbery polymers, glassy polymers are not at equilibrium state and effect of above process parameters are much more complex and highly non-linear. A thermodynamically consistent approach (NET-GP) was introduced around twenty years ago [Doghieri, F; Sarti, GC (1996) “Nonequilibrium lattice fluids: A predictive model for the solubility in glassy polymers” MACROMOLECULES, vol.29 (24), pag.7885-7896] to extend the application of standard equilibrium thermodynamic expression for free energy and chemical potential of polymer/solute systems below the glass transition temperature. The approach proved to be successful in the representation of effect of temperature, pressure and gas composition in glassy polymers, provided the equilibrium volumetric behavior of the latter is known, together with mass density in actual non-equilibrium conditions. For each polymeric species, experimental data for two distinct gaseous species in a relatively wide pressure range will be selected to retrieve model parameters for the given polymer. The model procedure will be then used to attempt for the prediction of gas solubility for all other gases of interest, at different pressure, for the same polymeric species.