DERIVATION OF THE CONSISTENT OSMOTIC VIRIAL EQUATION AND ITS APPLICATION TO AQUEOUS POLY(ETHYLENE-GLYCOL)-DEXTRAN 2-PHASE SYSTEMS

Based on the osmotic virial equation by McMillan and Mayer, thermodyna mically consistent expressions for the Gibbs free energy of mixing and the chemical potentials of the solutes are derived. In this derivatio n the concentration dependence of the specific volume is accounted for explicitly. The omostic virial coefficients are determined from water -activity data in binary and ternary solutions of poly(ethylene glycol ) and dextran of various molecular weights. This consistent osmotic vi rial equation is then tested to predict the Liquid-liquid equilibria o f the ternary systems. On the basis of the parameters obtained solely from water activities the concentrations as well as the molecular-weig ht distributions of the polymers in the coexisting liquid phases of th e aqueous two-phase systems can be predicted in goad agreement with th e experimental data.