Phase separation of aqueous mixtures of poly(ethylene oxide) and dextran

The phase behavior of aqueous mixtures of poly(ethylene oxide) (PEO) and dextran is studied as a function of the polymer concentration, the PEO molar mass, and temperature. The molar mass distributions of the two polymers in the coexisting phases are measured. From the temperature dependence we conclude that the phase separation between PEO and dextran is partially caused by sterical interactions. From the equilibrium phase volumes of the phase-separated mixture and the shape of the temperature-composition phase diagram of PEO and dextran, we conclude that also a decrease of the solvent quality of water for PEO at increasing temperatures is involved. It is suggested that the characteristics of the PEO-water interaction can affect the degree of fractionation. This suggestion is based on the observation that the degree of fractionation is not a simple exponential function of the molar mass. The phase behavior of the mixture PEO/dextran is compared to the previously studied phase behavior of the aqueous mixture of gelatin and dextran.