Two imidazolium-based ionic liquids, 1-ethyl-3-methyl imidazolium methylsufate (C(2)C(1)imC(1)SO(4)) and 1 ethyl -3-methyl imidazolium ethylsulfate (C(2)C(1)imC(2)SO(4)), 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. (C) 2016 Elsevier Ltd.