Surface Tensions of Bis(trifluoromethylsulfonyl)imide Anion-Based Ionic Liquids

Experimental measurements of the surface tension of six imidazolium-, pyridinium-, pyrrolidinium-, and phosphonium-based ionic liquids (ILs) with NTf2 as the common anion and their dependence with the temperatures of (293 to 353) K at atmospheric pressure are presented. The set of selected ILs was chosen to investigate the influence of the length and position of the cation alkyl chain and the cation family on the surface tension of the ILs based on the NTf2 anion. The surface thermodynamic functions such as surface entropy and enthalpy were derived from the temperature dependence of the surface tension, and their values indicate the importance of the surface ordering in ILs. The use of the Guggenheim and Eötvos correlations for the estimation of the critical temperatures of ILs is discussed, and a quantitative structure-property relationship (QSPR) correlation, previously extended for ILs, is here extended for the studied cations.