Micelle formation of Tween 20 nonionic surfactant in imidazolium ionic liquids

Abstract

Abstract Aggregation behavior of polyoxyethylene (POE)-type nonionic surfactant Tween 20 in imidazolium ionic liquids with varying chain length and different anions, such as tetrafluoroborate, hexafluorophosphate, bis(trifluoromethanesulfonyl)imide, and trifluoromethanesulfonate, was investigated by means of surface tension, conductivity and dynamic light scattering measurements. The role of the chain length, anion size as well as interactions between ions forming ionic liquid, were discussed in terms of an ability to support micelle formation. The ability of ionic liquids to induce and control self-aggregation of amphiphilic molecules by introducing a mixture of ionic liquids with different anions was also presented. Thermodynamic parameters of Tween 20 micellization in 1-ethyl-3-methylimidazolium trifluoromethanesulfonate were estimated using the dependence of critical micelle concentration on temperature. The normalized conductivity data were analyzed basing on the effective-medium approximation theories and used for determination of the number of ionic liquid cations associated with oxyethylene units of Tween 20. The results reflect an influence of cation volume as well as strength of ionic liquid cation and anion interactions, on its solvation and incorporation of ionic liquid molecules in the structure of the micelle.