Surface Tension Measurements for Four 1-Alkyl-3-methylimidazolium-Based Ionic Liquids with Hexafluorophosphate Anion

Abstract

Air−liquid interfacial surface tension measurements were performed on four 1-alkyl-3-methylimidazolium-based ([Cnmim], n = 3, 4, 6, 8) ionic liquids at 15 temperatures from (287 to 353) K at atmospheric pressure. To validate the accuracy of the results, the Wilhelmy plate method and the du Noüy ring method were employed in parallel using the Krűss K100MK2 tensiometer. At each temperature, from 33 to 55 Wilhelmy plate and from 10 to 30 du Noüy ring individual readings were taken in most cases. The surface tension average values at particular temperatures are presented with estimated overall standard uncertainty of 0.05 mN·m−1. An empirical surface tension−temperature equation has been developed describing the temperature dependence of each ionic liquid surface tension. To the 69 up-to-now published surface tension values of the above-mentioned four ionic liquids, the present study adds an additional 102 data points representing means calculated from about 3000 individual surface tension readings that altogether have been taken.