Solvation and aggregation of N,N′-dialkylimidazolium ionic liquids: A multinuclear NMR spectroscopy and molecular dynamics simulation study

The solvation and aggregation of the ionic liquid (IL) 1-n-butyl-3- methylimidazolium chloride ([C₄mim]Cl) in water and dimethylsulfoxide (DMSO) were examined by analysis of ¹H and ^35/37Cl chemical shift perturbations and molecular dynamics (MD) simulations. Evidence of aggregation of the IL n-butyl chains in aqueous environments at IL concentrations of 75-80 wt% was observed both in the NMR experiments and in the MD simulations. The studies also show that [C₄mim]Cl behaves as a typical electrolyte in water, with both ions completely solvated at low concentrations. On the other hand, the data reveal that the interactions between the [C₄mim]⁺ and Cl^- ions strengthen as the DMSO content of the solutions increases, and IL-rich clusters persist in this solvent even at concentrations below 10 wt%. These results provide an experimentally supported atomistic explanation of the effects that these two solvents have on some of the macroscopic properties of [C₄mim]Cl. The implications that these findings could have on the design of IL-based solvent systems are briefly discussed.