Viscosity, Interfacial Tension, Self-Diffusion Coefficient, Density, and Refractive Index of the Ionic Liquid 1-Ethyl-3-methylimidazolium Tetracyanoborate as a Function of Temperature at Atmospheric Pressure

Thermophysical properties of the ionic liquid (IL) [EMIM]­[B­(CN)4] (1-ethyl-3-methylimidazolium tetracyanoborate) were investigated both by conventional techniques and by surface light scattering (SLS) at atmospheric pressure. The density was measured between (283.15 and 363.15) K with a vibrating U-tube densimeter. An Abbe refractometer was used for the measurement of the refractive index in the range from (283.15 to 313.15) K. Self-diffusion coefficients for the cation and anion were measured by nuclear magnetic resonance (NMR) spectroscopy from (273.15 to 318.15) K. The interfacial tension was obtained from the pendant drop technique at 297.04 K. Based on this datum and the temperature dependence of density, the interfacial tension for all relevant temperatures was estimated via an appropriate prediction model. For the IL studied within the present work, the quantity directly accessible by SLS at low temperatures was the ratio of dynamic viscosity to interfacial tension. Combining the results from SLS with the density and interfacial tension data obtained from conventional methods, the dynamic viscosity could be determined from (283.15 to 303.15) K. For higher temperatures, SLS measurements combined with the results for density allowed the simultaneous determination of dynamic viscosity and interfacial tension from (313.15 to 363.15) K. Besides a comparison with literature data for [EMIM]­[B­(CN)4], the influence of variation of the anion in [EMIM]-based ILs on thermophysical properties is discussed. It could be shown that the thermophysical properties of [EMIM]­[B­(CN)4] are mainly affected by the distinct charge delocalization in the anion.