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

► Experimental data on temperature dependence of air-liquid interfacial tension at 1 b. ► 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.