A comparison of analytic thermodynamic models for gas solubility, volume dilation and heat of sorption in glassy polymeric materials

Gas sorption in polymeric materials results in gravimetric, volumetric and energetic changes. The ability to control these changes, through proper material selection, is critical in gas separation and barrier applications. We examine two analytic models for gas sorption that explicitly account for each of these changes: the elastic solid theory (ES) and the non-equilibrium lattice fluid theory (NELF). Model correlations and predictions are compared for carbon dioxide sorption in polycarbonate and tetramethyl polycarbonate. The ES model provides good correlation of sorption data using values for the carbon dioxide partial molar volume that are in good agreement with experimental data. By assigning an appropriate heat of vaporization to the carbon dioxide reference state, the model also provides good correlation of heat of sorption data. The NELF model provides good correlation of sorption data given the carbon dioxide partial molar volume data. Predicted enthalpy changes are in good agreement with the experiment but the effects of conditioning and molecular modification are not captured well. Both models are not capable of a priori predictions.