Thermodynamics of phase separation in aqueous solutions of polymers

Abstract

Abstract A thermodynamic theory for small-molecule systems, developed in our previous work (Yu et al., 1992), is extended to describe the phase separation of aqueous polymer solutions by modifying the combinatorial term to correct the overly large combinatorial contribution. Our model is based on the physical picture of Hirchfelder (1937). The hydrogen bonds between unlike components are dealt with using a cross association model, the excess entropy introduced by mixing molecular species with Flory-Huggins theory and the intermolecular interaction with NRTL model. Although polymers are commonly mixtures with a molecular weight distribution of finite width, we treat them as single components. Theoretical predictions of phase equilibria from this model are in good agreement with experimental findings for the systems of PEG-water and PPG-water.