Thermodynamics and phase separation phenomenon of polyoxyethylene sorbitan monolaurate in micellar solutions containing inorganic salts

Abstract

Abstract The phase separation behavior of polyoxyethylene sorbitan monolaurate (1.000 mmol/L) was investigated in aqueous micellar solution containing inorganic salt, especially the high concentration of different cationic chlorides including NaCl, KCl, MgCl2, CaCl2, BaCl2 and AlCl3. The continuous decrease in the cloud point (CP) was observed on adding the univalent cationic chlorides (NaCl and KCl). While the addition of multivalent cationic chlorides initially depress the phase separation and then promote the solvation of surfactant in water phase. The relationship between the reciprocal of CP and the concentration of inorganic salt is found to well linearize in the range of a certain concentration of inorganic salt. The dependence of related constant terms in the obtained equations on the nature of inorganic ions was theoretically discussed. The ionic charge vs. atom radium ratio was also used to probe the difference in the effect of different cations on the phase separation. In the framework of phase separation model, the obtained thermodynamic parameters indicate that the process of phase separation is non-spontaneous and the entropy makes an overwhelming contribution.