Aqueous two-phase systems containing imidazolium ionic liquids and a Tween surfactant

Highlights: • Short chain imidazolium ionic liquids suitably salt out aqueous surfactants solutions. • Immiscibility region was defined by the cloud point method at different temperatures. • Different empirical equations turned out to correlate binodal and tie-line data. - Abstract: Two imidazolium-based ionic liquids, 1-ethyl-3-methyl imidazolium methylsufate (C₂C₁imC₁SO₄) and 1-ethyl-3-methyl imidazolium ethylsulfate (C₂C₁imC₂SO₄), were tested as contenders for phase segregation in aqueous solutions of a non-ionic surfactant belonging to Tween family (Tween 20). Several empirical equations were used to correlate the binodal results which were previously obtained by means of the cloud point method at temperatures ranging from T = (298.15–333.15) K. The tie-lines have been determined by means of density and refractive indices measurement, and the Othmer-Tobias model was used to elucidate the thermodynamic consistence of these experimental values.