Influence of the anion on the surface tension of 1-ethyl-3-methylimidazolium-based ionic liquids

The air–liquid interfacial tensions of eight ionic liquids, from (298 to 343) K, are presented in this work. The studied ionic liquids are formed by the fixed 1-ethyl-3-methylimidazolium cation combined with the anions acetate, dicyanamide, dimethylphosphate, methylphosphonate, methanesulfonate, thiocyanate, tosylate, and trifluoromethanesulfonate. The selected ionic liquids allowed a comprehensive study through the influence of the anion nature on the surface tension and on their surface ordering. A slight dependence of the surface tension with the ionic liquid molar volume was identified. The surface thermodynamic functions are mainly controlled by the anion which constitutes a given ionic liquid. The hypothetical critical temperatures of all ionic liquids were estimated by means of the Eötvos and Guggenheim correlations and are presented.

► Novel surface tension data for ionic liquids are presented.
► The effect of the anion on the surface tension is evaluated.
► A correlation between the surface tension and the molar volume is presented.
► The surface thermodynamic properties are presented.
► The hypothetical critical temperatures are shown.