Dynamic and Structural Properties of Room Temperature Ionic Liquids Near Silica and Carbon Surfaces

The dynamics and structural properties of a room temperature ionic liquid (RTIL) 1-Butyl-3-Methyl-Imidazolium(trifluoromethanesulfonimide) ([C₄mim][Tf₂N]) confined in silica and carbon mesopores were investigated by molecular dynamics (MD) simulations and nuclear magnetic resonance (NMR) experiments. Different interfacial microstructures of confined [C₄mim][Tf₂N] were observed and the temperature-dependent diffusion coefficients of [C₄mim][Tf₂N] confined in silica or carbon mesopore exhibit divergent behavior. The effects of loading fraction on the magnitude of the diffusion coefficient in the silica pore are investigated and is found to display weaker temperature dependence as loading fraction decreases. The diffusion coefficients of mesoporous carbon-confined [C₄mim][Tf₂N] are relatively insensitive to the loading faction and exhibit temperature dependence that is similar to the bulk temperature dependence at all loading levels.  The unique surface heterogeneity, dissimilar interfacial microstructures, and interaction potential profile of RTILs near silica and carbon walls are shown to govern the differences exhibited in RTILs confined in mesoporous silica and carbon.