Ionic liquid dynamics measured with implanted-ion β-NMR

Ionic liquids (ILs) not only found in a wide range of potential applications, spanning energy storage to space travel, but the constituent ions have fascinating dynamics and structure. In this study, we use implanted-ion ⁸Li β-NMR to probe these dynamics in the IL 1-ethyl-3-methylimidazolium acetate. Sensitivity to nanosecond ⁸Li⁺ solvation dynamics is inferred from the motional narrowing of the resonance and the local maxima in the ⁸Li relaxation rate. We show that the activation energy and Vogel-Fulcher-Tammann temperature associated with the relaxation process agree with the dynamic viscosity. Near the melting point, the lineshape is broad and intense, and the form of the relaxation is non-exponential, reflective of heterogeneous dynamics. This demonstration establishes the feasibility of studing the local structure and dynamics of IL thin films and interfaces using β-NMR¹.

1. D. Fujimoto, et al., The dynamics of liquid 1-ethyl-3-methylimidazolium acetate measured with implanted-ion ⁸Li β-NMR, Chem. Mater. In press.