Interfacial tension of polyethylene glycol/potassium phosphate aqueous two-phase systems

The interfacial tension of Polyethylene glycol (PEG)/potassium phosphate two-phase systems was measured by the rotating drop method. The interfacial tension was as low as 0.001 dyne/cm and increased with increases in the total concentrations of both PEG and potassium phosphate in two-phase systems. The increase in the interfacial tension was a function of the concentration differences of PEG and potassium phosphate between the top and the bottom phases which was confirmed by the tie line analysis. The interfacial tension was affected also by the molecular weight of PEG. At low PEG molecular weights, the increase in the molecular weight greatly increased the interfacial tension, but at high molecular weights, the interfacial tension varied less with the molecular weight.