Influence of Water on Carbon Dioxide and Room Temperature Ionic Liquid Dynamics: Supported Ionic Liquid Membrane vs the Bulk Liquid.

The influence of water on the dynamics of a room temperature ionic liquid (RTIL), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimNTf), and CO in the RTIL was studied in the bulk liquid and a supported ionic liquid membrane (SILM) using two-dimensional infrared (IR) and IR polarization selective pump-probe spectroscopies. In the water-saturated bulk EmimNTf, the complete orientational randomization and structural spectral diffusion (SSD) of CO became faster than in the dry EmimNTf. In the poly(ether sulfone) SILM, only the longer time components of the SSD became faster in the water-saturated RTIL; the complete orientational randomization remained similar to the dry RTIL in the SILM. The implication is that the presence of water in EmimNTf contained in the SILM facilitates the fluctuation of globally modified RTIL structure in the pores, but the local RTIL environments are relatively unaffected.