화학공학소재연구정보센터
Journal of Physical Chemistry B, Vol.115, No.31, 9662-9670, 2011
Effect of SO2 on the Transport Properties of an Imidazolium Ionic Liquid and Its Lithium Solution
Transport coefficients have been measured as a function of the concentration of sulfur dioxide, SO2, dissolved in 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)-imide, [BMMI][Tf2N], as well as in its lithium salt solution, Li[Tf2N]. The SO2 reduces viscosity and density and increases conductivity and diffusion coefficients in both the neat [BMMI] [Tf2N] and the [BMMI][Tf2N]-Li[Tf2N] solution. The conductivity enhancement is not assigned to a simple viscosity effect; the weakening of ionic interactions upon SO2 addition also plays a role. Microscopic details of the SO2 effect were unraveled using Raman spectroscopy and molecular dynamics (MD) simulations. The Raman spectra suggest that the Li+-[Tf2N] interaction is barely affected by SO2, and the SO2-[Tf2N] interaction is weaker than previously observed in an investigation of an ionic liquid containing the bromide anion. Transport coefficients calculated by MD simulations show the same trend as the experimental data with respect to SO2 content. The MD simulations provide structural information on SO2 molecules around [Tf2N], in particular the interaction of the sulfur atom of SO2 with oxygen and fluorine atoms of the anion. The SO2-[BMMI] interaction is also important because the [BMMI] cations with above-average mobility have a larger number of nearest-neighbor SO2 molecules.