A new theoretical model – The ionic molar surface Gibbs free energy and its application.

Three novel ether-functionalized ionic liquids (ILs) 1-ethyl-3-(2-methoxyethyl)-imidazolium acetate, [C 2 2O1IM][OAc], 1-ethyl-3-(2-methoxyethyl)-imidazolium thiocyanate, [C 2 2O1IM][SCN], 1-ethyl-3-(2-methoxyethyl)-imidazolium trifluoromethanesulfonate, [C 2 2O1IM][TfO], and two ILs 1-ethyl-3-(2-methoxyethyl)-imidazolium dicyanamide, [C 2 2O1IM][DCA], 1-ethyl-3-(2-methoxyethyl)-imidazolium bis(trifluoromethylsulfonyl)imide, [C 2 2O1IM][NTF 2 ] were prepared and characterized. Their density and surface tension were measured at T = (298.15–338.15) K. As a new theoretical model, the ionic molar surface Gibbs free energy, g i , was put forward. The ionic molar surface Gibbs free energy, g − , for [BF 4 ] − , which was as reference ion, was obtained in terms of the extrathermodynamic assumptions so that the ionic molar surface Gibbs free energy, g + , of the corresponding cations, [C n mim] + (n = 2–6), were determined. In terms of the g + values of [C n mim] + (n = 2–6), the g − values of 12 kinds of anions were determined and then the average g + value of [C 2 2O1IM] + (9.52 ± 0.21 kJ·mol −1 ) was gotten. By using the values of these g i , the predicted values of molar surface Gibbs free energy, g est , and surface tension, γ est , for [C 2 2O1IM][X] (X = OAC, SCN, DCA, TfO, NTF 2 ) and other 45 ionic liquids were estimated. In comparison, the predicted values correlated quite well with their matching experimental values. [ABSTRACT FROM AUTHOR]