Predicting Gas Solubility in Glassy Polymers through Nonequilibrium EOS

The non-equilibrium thermodynamic approach to describing properties of glassy polymers, earlier applied in the so-called NELF model using Lattice Fluid Theory, is generalized to the use of arbitrary equations of state. Application to Statistical Associating Fluid Theory (SAFT) is discussed in detail and use of this approach to predict opr correlate gas solubility in glassy polymers is presented for the case of low-pressure sorption. Prediction procedures rely on volumetric data for the pure polymer and gaseous species, while for data correlation a temperature independent binary interaction coefficient is used as an adjustable parameter. Results from model calculations are compared with literature data for gas solubility in polycarbonate and polysulfone. Analysis of solubility coefficient variations above and below the glass transition temperature indicates thet the non-equilibrium approach is the proper procedure to extend an EoS description of thermodynamic properties to the glassy state.