NMR Diffusion Measurements as a Simple Method to Examine Solvent–Solvent and Solvent–Solute Interactions in Mixtures of the Ionic Liquid [Bmim][N(SO2CF3)2] and Acetonitrile

The self-diffusion coefficients of each component in mixtures of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Bmim][N(SO2CF3)2]) and acetonitrile were determined. The results suggest that the hydrodynamic boundary conditions changing from 'stick' to 'slip' as the solvent composition transitions from 'ionic liquid dissolved in acetonitrile' (χIL 0.4). At higher χIL the acetonitrile species are affected by 'cage' and 'jump' events, as the acetonitrile molecules reside nearer to the charged centre on the ions than in the 'non-polar' regions. The self-diffusion coefficients of hexan-1-amine, dipropylamine, 1-hexanol and dipropylether in mixtures of [Bmim][N(SO2CF3)2] and acetonitrile were determined. In general the nitrogen-containing solutes were found to diffuse slower than the oxygen-containing solutes; this indicates that there are greater ionic liquid - N interactions than ionic liquid - O interactions. This work demonstrates that the self-diffusion coefficients of species can provide valuable information about solvent - solvent and solvent - solute interactions in mixtures containing an ionic liquid.