A NEW EXCLUDED-VOLUME THEORY AND ITS APPLICATION TO THE COEXISTENCE CURVES OF AQUEOUS POLYMER 2-PHASE SYSTEMS

A theoretical description of the coexistence curves of binary and some ternary systems has been developed using methods of statistical geome try. It is based on the concept that macroscopically any molecular spe cies in a solution is distributed at random and that every system comp osition on the binodal is a geometrically saturated solution of each s olute in the presence of the other. The link between the model and the rmodynamics is also established. The model has been applied to aqueous polydisperse polymer two-phase systems, and it is shown that when the molecular weights of the two phase-forming components are rather disp arate, only one parameter, the effective excluded volume, is needed to reproduce experimental coexistence curves for polyethylene glycol-Dex tran-water systems. The current model has been compared with some othe r approaches (lattice solution theories, treatments based on the Setsc henow equation) and the deficiencies of the Setschenow equation and th e current model have been commented on.