The Cloud Point Behaviors and the Liquid–Liquid Equilibrium of L31—Inorganic Sodium Salt Aqueous Two-Phase Systems

Abstract

The cloud point (CP) of triblock-copolymer L31 aqueous solution was determined with salting-out salts (Na₂SO₄/Na₂CO₃/NaF/NaCl/NaBr). The results show that all these salts can decrease the CP of L31 aqueous solution and form aqueous two-phase system (ATPS). With increasing concentrations of Na₂SO₄ and Na₂CO₃, an obvious phase inversion could be observed and phase inversion points were found. This was mainly due to the change in density, the salt-rich phase shifted from the top phase to the bottom phase. Meanwhile, the liquid-liquid equilibrium (LLE) data for L31-Na₂SO₄/Na₂CO₃/NaF/NaCl/NaBr ATPSs were measured at 288.15 K. The salt ability to decrease the CP and to induce the phase separation is as follows: Na₂SO₄ > Na₂CO₃, NaF > NaCl > NaBr. Finally, the order of anions that reduced the CP and caused phase separation was obtained as follows: SO₄²⁻ >CO₃²⁻, F⁻ > Cl⁻ > Br⁻.

Graphical Abstract

Keywords:

• L31
• inorganic sodium salt
• the cloud point
• the liquid-liquid equilibrium
• phase inversion

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [Nos. 31470434, 21576124 and 21676124], China Postdoctoral Science Foundation [No. 2017M610308], and Postdoctoral Science Foundation of Jiangsu Province [No. 1701107B].