Phase separation dynamics in oil-polymer-salt-water three-liquid-phase system: Effect of phase-forming salt

Effect of phase-forming salts on the phase separation dynamics of the three-liquid-phase system, composed of tributyl phosphate (TBP) and PEG2000-salts aqueous two phases, was investigated. We found the species of salts exhibited almost no effect on the separation rate of oil top phase and polymer middle phase from salt aqueous bottom phase, however separation between oil top phase and polymer middle phase became slow with the increase of salting-out ability of the ions present in the slats. Theoretical analysis were provided why aggregation of dispersed oil drops in polymer phase and dispersed polymer drops in oil phase slowed down with increasing the salting-out ability. The effect of salts on the Van der Waals attraction potential energy among dispersed oil or polymer drops, and the hydrophobicity difference between oil and polymer phase play a crucial role. The present work promotes our understanding into the essence of phase-forming salts in three-liquid-phase separation processes.