Thermodynamics of aqueous solutions of poly(propylene glycol) + sodium phosphate salts at different temperatures

It has long been recognized that the mixture of aqueous solutions of some incompatible polymers or of some polymers and electrolytes forms a stable two-phase liquid system, where the only solvent is water. Aqueous two-phase systems of this nature can be useful for the separation and purification of biomaterials where the employment of a non-polar solvent/aqueous phase system would lead to degradation of biological activity [1,2]. Thermodynamic properties of aqueous polymer-salt systems are necessary for a fundamental understanding of the phase-forming ability and also for the development of theoretical models for the prediction of the partitioning behaviour of the two-phase system. In this work, precise density, sound velocity, viscosity, phase diagram and liquid-liquid equilibrium (LLE) measurements have been carried out on polypropylene glycol (PPG) in aqueous solutions of sodium dihydrogen phosphate, di-sodium hydrogen phosphate and tri-sodium phosphate over a range of temperatures at atmospheric pressure.