Surface tension of 1-alkyl-3-methylimidazolium based ionic liquids with trifluoromethanesulfonate and tetrafluoroborate anion

• Published in: Fluid phase equilibria Vol. 303; no. 2; pp. 184 - 190
• Main Authors: Součková, Monika, Klomfar, Jaroslav, Pátek, Jaroslav
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 25.04.2011; Elsevier
• Subjects: Anions; Cations; Chains; Chemistry; Data points; Entropy; Exact sciences and technology; General and physical chemistry; Interfacial tension; Ionic liquid; Ionic liquids; Solutions; Surface tension; Tetrafluoroborate; Trifluoromethanesulfonate; Tetrafluoroborate; Trifluoromethanesulfonate; Surface tension; Ionic liquid; Surface properties
• ISSN: 0378-3812; 1879-0224
• DOI: 10.1016/j.fluid.2011.01.027

► Experimental data on temperature dependence of air–liquid interfacial tension at 1b. ► Five imidazolium trifluoromethanesulfonate and tetrafluoroborate ionic liquids. ► The surface tension of the ionic liquids decreases with the cation alkyl chain length. ► The surface entropy of ionic liquids increases with the cation alkyl chain length. ► The surface tension of the ionic liquids increases with decreasing anion size. The amount of available accurate experimental data on the surface tension of ionic liquids is still limited; in many cases the data are rare or even absent. In the present study, air–liquid interfacial tension data were determined experimentally for five 1-Cn-3-methylimidazolium based ionic liquids (n=2, 4, and 6), three with trifluoromethanesulfonate and two with tetrafluoroborate anion, at atmospheric pressure in the temperature range from 268 to 356K. The resultant surface tension data are average values of the measurements repeated many times at each set point temperature. The accuracy of the results, was confirmed by employing the Wilhelmy plate and the du Noüy ring methods in parallel, using the Krüss K100MK2 tensiometer. For the Wilhelmy plate data the combined standard uncertainty is estimated to be about 0.05mNm−1. The data obtained by du Noüy method show about up to seven times greater scatter than those obtained by the Wilhelmy plate method. To the 50 up to now published surface tension values for the five studied ionic liquids the present study adds further 175 data points. In contrast to that of n-alkanes, the surface tension of 1-alkyl-3-methylimidazolium based ionic liquids decreases and their surface entropy increases with the cation alkyl chain length.