Liquid–Liquid Equilibrium Data of Ternary Mixture of Polymer, Sodium Thiosulfate, and Water: Effect of Type and Molar Mass of Macromolecule

Experimental liquid–liquid equilibrium data were obtained for aqueous two-phase systems (ATPS) formed by macromolecule (L64, F68, poly(ethylene glycol) 10,000 (PEG10k) or 35,000 (PEG35k) g·mol–1) + sodium thiosulfate + water at temperatures of 278.15, 288.15, and 298.15 K, and 0.09 MPa. The temperature effect had no statistically significant effect on the position of solubility curves; therefore, this process is entropically driven. Lower concentrations of F68 are required for phase segregation compared to L64, indicating a greater effect of molar mass than of copolymer hydrophobicity on binodal curve position. For this same reason, PEG35k has a larger biphasic region than PEG10k. When comparing polymer types, the two macromolecules used to perform this comparison have close molar masses (8400 and 10,000 g·mol–1). F68 induces phase segregation at slightly lower concentrations than PEG10k; therefore, this behavior is due to the hydrophobic groups present in the copolymer. The experimental data were mathematically fitted with Merchuk's model for the binodal curves since the values of obtained absolute average deviations show that the models provided excellent performance for regression of the experimental data.