Extension of the Wilson model to multicomponent polymer solutions: applications to polymer-polymer aqueous two-phase systems

The Wilson model for non-electrolytes has been extended for the representation of the excess Gibbs energy of multicomponent polymer solutions. The excess Gibbs energy of a polymer solution is expressed as a sum of contributions of a combinatorial and a residual excess Gibbs energy term. The contribution of the combinatorial excess Gibbs energy is represented by the Flory-Huggins expression. A new expression based on the local composition concept, which is a modified Wilson model, has been developed to account for the contribution of the residual excess Gibbs energy. The model has been applied to several polymer-polymer aqueous two-phase systems. The results show that the model is reliable both for correlation and prediction of the liquid-liquid equilibrium phase diagrams of aqueous two-phase systems at different polymer molecular weights.