Investigation of Dynamic Behavior of Confined Ionic Liquid [BMIM]⁺[TCM]^- in Silica Material SBA-15 Using NMR

The molecular dynamics of 1-butyl-3-methyl imidazolium tricyanomethanide ionic liquid [BMIM]⁺[TCM]^- confined in SBA-15 mesoporous silica were examined using ¹H NMR spin-lattice (T₁) relaxation and diffusion measurements. An extensive temperature range (100 K-400 K) was considered in order to study both the liquid and glassy states. The hydrogen dynamics in the two states and the self-diffusion coefficients of the cation [BMIM]⁺ above the glass transition temperature were extracted from the experimental data. The results were then compared to the corresponding bulk substance. The effects of confinement on the dynamic properties of the ionic liquid clearly manifest themselves in both temperature regimes. In the high-temperature liquid state, the mobility of the confined cations reduces significantly compared to the bulk; interestingly, confinement drives the ionic liquid to the glassy state at a higher temperature T_g than the bulk ionic liquid, whereas an unusual T₁ temperature dependence is observed in the high-temperature regime, assigned to the interaction of the ionic liquid with the silica-OH species.