Cloudy behavior and equilibrium phase behavior of triblock copolymer L64+salt + water two-phase systems

The cloud point (CP) values of aqueous solutions of the triblock copolymer L64 were determined in the absence and presence of five salting-out salts (K2SO4, Na2SO4, (NH4)(2)SO4, K2CO3, K2HPO4) at different concentrations. All the five salts could decrease the CP values and form aqueous two phase systems (ATPSs) with L64. A notable phase inversion phenomenon occurred with the increasing salt concentrations and the phase inversion points were found. The salt-rich phase transferred from the top phase to the bottom phase because of the change of density. Liquid-liquid equilibrium (LLE) data of these ATPSs were measured at 45 degrees C, respectively. The consistency of the tie-lines was verified by using the empirical equations from the Othmer-Tobias and Bancroft correlation. The effects on the cloudy behavior and phase separation depended on the salting-out ability. The results showed that the salting-out ability of the cations followed the order: Na+ > K+ > NH4+; the anions followed the order: HPO42- > SO42- > CO32-. It could be concluded that using the Gibbs free energy of hydration of the ions (A.GHyd) to estimate salting-out ability was not suitable for all of the ATPSs. (C) 2015 Elsevier B.V. All rights reserved.