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Ion association of the ionic liquid [bmim][Cl] in acetonitrile and in water was studied by dielectric spectroscopy for salt concentrations c r 1. Only contact ion pairs were detected in both solvents. Standard-state enthalpy, entropy and heat capacity changes of ion association were derived, as well as the activation enthalpy of charge transport and the limiting conductivity of the cation, l). These data, in conjunction with effective solvation numbers obtained from the dielectric spectra, suggest that the solvation of [bmim] + is much weaker in water than in acetonitrile.

A systematic investigation of influence of the length of the side alkyl chain and the counter ions on the thermodynamic of the micellization process at imidazolium based surface active ionic liquids (SAILs) in aqueous solution was carried out by isothermal titration calorimetry (ITC) in a broad temperature range. The effect of alkyl chain length on the micellization process in water has been investigated on 1decyl-3-methylimidazolium ([C 10 mim]Cl) 1-dodecyl-3-methylimidazolium ([C 12 mim]Cl), 1tetradecyl-3-methylimidazolium ([C 14 mim]Cl) and 1-hexadecyl-3-methylimidazolium ([C 16 mim]Cl) chlorides, whereas the influence of counterion was studied at the micellization of 1-dodecyl-3-methylimidazolium chloride ([C 12 mim]Cl), bromide ([C 12 mim]Br), iodide ([C 12 mim]I), acetate ([C 12 mim]OAc), methanesulfonate ([C 12 mim]OMs), toluensulfonate (([C 12 mim]OTs), trifluromethane sulfonate ([C 12 mim]OTf), trifluoro acetate (([C 12 mim]TFA) and salicylate ([C 12 mim]Sal) in water.

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Molar conductivities, Λ, of dilute solutions of the ionic liquids (ILs) 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF4]), 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), 1-hexyl-3-methylimidazolium tetrafluoroborate ([hmim][BF4]), and 1-hexyl-3-methylimidazolium bis-(trifluoromethanesulfonyl)amide ([hmim][NTf2]) in acetonitrile (AN) were determined as a function of temperature in the range 273.15-313.15 K. The data were analyzed with Barthel’s lcCM model to obtain limiting molar conductivities, Λ(∞)(T), and association constants, K(A)°(T) of these electrolytes. The temperature dependence of these parameters, as well as the extracted limiting cation conductivities, λ(i)(∞), were discussed. Additionally, dielectric spectra for [hmim][NTf2] + AN were analyzed in terms of ion association and ion solvation and compared with the inference from conductivity. It appears that in dilute solutions the imidazolium ring of the cations is solvated by ∼6 AN molecules that are slowed by a factor of ∼8-10 compared to the bulk-solvent dynamics. Ion association of imidazolium ILs to contact ion pairs is only moderate, similar to common 1:1 electrolytes in this solvent.

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