APPLICATION OF A STATISTICAL GEOMETRICAL-THEORY TO AQUEOUS 2-PHASE SYSTEMS

In a recent publication, we presented a novel theory based on a statis tical geometric concepts which gave a simple analytical expression for the coexistence curves (binodals) of aqueous two-phase systems. In th e present paper, this theory (which we term the binodal model) has bee n applied, with considerable success, to polymer + polymer and polymer + salt aqueous two-phase systems. For polyethylene glycol (PEG) + Dex tran (Dex) aqueous two-phase systems, the binodal model gives satisfac tory agreement with experiment when the molar mass ratio of Dex to PEG greater than or equal to ca. 4. For PEG + salt aqueous two-phase syst ems, where the molar mass ratio of PEG to salt is almost invariably la rge, the binodal model works well. The model also explains the influen ce of both temperature and polymer molar mass on binodals and confirms the experimental observation found for some systems that under some c ircumstances the lower-molar-mass polymer can induce phase separation at lower concentrations than the polymer with the higher molar mass.