The transport and conductivity properties of the ionic liquid EMIMTCM

The ionic liquid 1-ethyl-3-methylimidazolium tricyanomethanide (EMIMTCM) is a very interesting, yet so far poorly studied, ionic liquid which has a low viscosity, high conductivity, and acceptable electrochemical stability for use as an electrolyte. In this study the self-diffusion coefficients, spin-lattice relaxation times, and spin-spin relaxation times of EMIMTCM were measured over the temperature range 263 to 343 K. To gain insight into the origin of the physical properties of EMIMTCM, the temperature dependence of the measured cation diffusion coefficient was compared with two structurally related EMIM-based ionic liquids which differed only in the choice of anion: 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)amide (EMIMFSA) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulphonyl)amine (EMIMTFSA). The experimentally determined diffusion coefficient, conductivity, and viscosity values were analysed using the Stokes-Einstein-Sutherland, Stokes-Einstein-Debye and Vogel-Fulcher-Tamman equations, respectively. The correlation time (τcation) of the cations were calculated from the relaxation data using the Bloembergen-Purcell-Pound equation. The overall isotropic molecular reorientational correlation time, τc, and translational correlation time, τD, of the cations were calculated from the viscosity and translational diffusion coefficients, respectively. The results of this study provide information on reorientational and translational motions of EMIMTCM and the correlation times were found to be in the following order τD > τc > τcation and EMIMTCM diffused faster than EMIMTFSA and EMIMFSA, due to the smaller size of the TCM anion and its lower viscosity.