Aggregation Behavior of Several Ionic Liquids in Molecular Solvents of Low Polarity--Indication of a Bimodal Distribution.

The structure and dynamics of ion pairing and aggregation is studied by concentration- and temperature-dependent measurements of (1) H and (19) F self-diffusion coefficients, viscosity, and conductivity for the following five solutions: 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([Cn mim][NTf2], n=2, 4, 6) in dichloromethane (CH2Cl2), and [C6 mim][NTf2] in tetrahydrofuran (THF) and chlorobenzene (C6 H5 Cl). The temperature dependence of these properties at constant IL concentrations follows the Arrhenius law for all five solutions. The IL-concentration dependence of the respective activation energies obtained from the Arrhenius analysis is nonlinear in the case of conductivity, but indicates linear relationships for viscosity and self-diffusion.