Application of a statistical geometrical theory to aqueous two-phase systems

Abstract

In a recent publication, we presented a novel theory based on a statistical geometric concepts which gave a simple analytical expression for the coexistence curves (binodals) of aqueous two-phase systems. In the present paper, this theory (which we term the binodal model) has been applied, with considerable success, to polymer + polymer and polymer + salt aqueous two-phase systems. For polyethylene glycol (PEG) + Dextran (Dex) aqueous two-phase systems, the binodal model gives satisfactory agreement with experiment when the molar mass ratio of Dex to PEG ⩾ ca. 4. For PEG + salt aqueous two-phase systems, where the molar mass ratio of PEG to salt is almost invariably large, the binodal model works well. The model also explains the influence of both temperature and polymer molar mass on binodals and confirms the experimental observation found for some systems that under some circumstances the lower-molar-mass polymer can induce phase separation at lower concentrations than the polymer with the higher molar mass.