Yong Zhang published a paper entitled "The Effect of C2 Substitution on Melting Points and Liquid Phase Dynamics of Imidazolium-Based Ionic Liquids: Insights from Molecular Dynamics Simulations”, in Physical Chemistry Chemical Physics, 2012, 14(35), 12157-12164. In it, he provided detailed evidence that entropic effects play a big role in determining the melting point and viscosity trends observed when the C2 carbon of imidazolium-based ionic liquids is methylated.
The origin of higher melting points of C2 methylated alkyl-imidazolium PF6 ionic liquids is mainly entropic.
Andrew Paluch, Cameron Vitter and Jindal Shah published a paper entitled “A Comparison of the Solvation Thermodynamics of Amino Acid Analogues in Water, 1-Octanol and 1-n-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide Ionic Liquids by Molecular Simulation”, in Journal of Chemical Physics, 2012, 137, 184505. They developed a "hydrophobicity scale" and showed how expanded ensemble simulations can be used to quantitatively estimate the solvation thermodynamics of amino acid analogues in various solvents, including ionic liquids.
A comparison of the dimensionless molar entropy of transfer between solvent A and water, and lnK* computed at 328 K via molecular simulation. Solvent A corresponds to either 1-octanol, [emim]+ [Tf2 N]− , [bmim]+ [Tf2 N]− , [omim]+ [Tf2 N]− , or p-octanol, as indicated by the leg- end.