Physico-chemical features of solvent media in the phases of aqueous polymer two-phase systems

Solvent polarity and pH in the coexisting aqueous phases of aqueous dextran–poly(ethylene glycol) and dextran–Ficoll two‐phase systems of varied polymer concentrations were examined using the solvatochromic technique and potentiometric measurements, respectively. The relative solvent polarity of the phases, as measured by the solvatochromic technique, is suggested as a measure of the hydration power of water in the phases of aqueous polymer systems. Partitioning of a series of sulphonephthalein dyes in aqueous dextran–poly(ethylene glycol) and dextran–Ficoll two‐phase systems of fixed polymer composition containing 0.01 mol/L universal buffer, pH 7.15, was studied. The results obtained are discussed together with those reported earlier on the physico‐chemical features of aqueous media in the coexisting phases of the systems. It is suggested that the two phases of aqueous polymer systems should be viewed as two immiscible water‐like solvents. The implications of the suggestion for the theoretical treatment of aqueous polymer two‐phase systems are discussed.