Structure-property relationships in ILs: A study of the alkyl chain length dependence in vaporisation enthalpies of pyridinium based ionic liquids

The enthalpies of vaporization for the series of pyridinium-based ionic liquids with bis(trifluoromethylsulfonyl)imide anion [C _n Py][NTf₂] (n = 2, 3, 4, 5, and 6) have been determined with the quartz crystal microbalance technique combined with the Langmuir evaporation. The linear dependence of vaporization enthalpies on the chain length has been revealed. New approach based on volumetric, surface tension, and speed of sound measurements has been developed for estimation of heat capacity differences between gas and liquid phase, which were required for adjustment of measured vaporization enthalpies to the reference temperature 298 K.