Influence of the temperature and type of macromolecule on phase diagrams of aqueous two-phase systems

Phase diagrams for aqueous two-phase systems formed by L64 + Na2SO3 + H2O, F68 + Na2SO3 + H2O, polyethylene glycol 10,000 g·mol–1 (PEG10k) + Na2SO3 + H2O and PEG 35,000 g·mol–1 (PEG35k) + Na2SO3 + H2O were determined experimentally at temperatures of 278.15, 288.15 and 298.15 K, at 0.09 MPa. The binodal curve is not significantly shifted with varying temperature, indicating a small change on the system enthalpy during the phase separation process, but an increase in the temperature promoted an increase in the slope of tie-line. The effectiveness of macromolecules in promoting phase separation occurs in the following order: PEG35k > PEG10k ≈ F68 > L64. An increase in molar mass requires lower concentrations to induce phase separation, due to the decrease of configurational entropy of the solution. When comparing macromolecules with similar molar masses, PEG10k required slightly lower concentrations than F68 to induce phase segregation. Although PEG10k has a higher molar mass, the structure of F68 contains hydrophobic groups (poly(propylene glycol)) that compensate for its lower molar mass, which generates similar phase segregation induction capabilities. Therefore, new aqueous two-phase systems have been characterized by extending the range of systems available for applications.