We published a paper with several collaborators (Sergey Verevkin and co-workers in Rostock, Ingo Krossing and co-workers in Freiburg and Roland Kalb at Proionic in Austria) showing that the highly scattered experimental data on enthalpy of vaporization for a series of alkylimidazolium NTf2 ionic liquids can be made to appear much less "scattered" if the data are properly analyzed when extrapolating to a reference temperature of 298K. Two simple methods for doing the temperature adjustment are proposed. We also find that, although our molecular simulations see evidence for aggregation of alkyl tails when chains are longer than C4, this does not result in any breaks in the linear dependence of vaporization enthalpy of chain length. Both the simulations and experiments predict that vaporization enthalpy follows a simple group additivity rule not so different from many common liquids.
The figure on the left shows the contributions to the enthalpy of vaporization for alkylimidazolium NTf2 ionic liquids from van der Waals interactions (circles), Coulombic interactions (squares) and intramolecular contributions (diamonds). The total enthalpy is shown as triangles.
For more information, see: Sergey P. Verevkin, Dzmitry H. Zaitsau, Vladimir N. Emel’yanenko, Andrei V. Yermalayeu, Christoph Schick, Hongjun Liu and Edward J. Maginn, Safak Bulut and Ingo Krossing, and Roland Kalb “Making Sense of Enthalpy of Vaporization Trends for Ionic Liquids: New Experimental and Simulation Data Show a Simple Linear Relationship and Help Reconcile Previous Data”, Journal of Physical Chemistry B, 2013, 117, 6473-6486. http://dx.doi.org/10.1021/jp311429r