Temperature-dependent conductivity, viscosity, and density of four ionic liquids (ILs), 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([EMIM][NTf2]), and 1-ethyl-3-methylimidazolium dicyanamide ([EMIM][DCA]), were measured with high precision from +80 °C down to −35 °C, if possible. Fitting parameters for the Vogel−Fulcher−Tammann (VFT) equation were obtained for conductivity and viscosity data, and obtained data were analyzed with the help of the fractional Walden rule and the Walden plot. Excellent linear behavior is observed for all ILs; however, the average slope is not unity as expected for the ideal Walden rule, but 0.92 ± 0.02. The so-called ideal KCl line that is used to compare ILs within the Walden plot is discussed, as literature data for aqueous KCl solutions show that its assumed ideality has to be modified.
Temperature-dependent conductivity and viscosity data of over ten new fluoroborate-based ionic liquids (ILs) were measured in a temperature range spanning about 100 K. Data are presented and evaluated according to the fractional Walden rule and Angell’s fragility concept. All ILs show excellent linear relationships for their Walden plots with similar slopes in the range from about 0.90 to about 0.94. It was found empirically that the slopes of the Walden plots reflect the ratio of the corresponding Arrhenius activation energies for the ILs’ temperature-dependent viscosities and molar conductivities. Further analysis of viscosity data of ILs leads to the conclusion that all investigated ILs, including some more common ones, can be classified as highly fragile, very weak liquids, reaching even the limiting value estimated by Vilgis.
We demonstrate here that microemulsions with an IL as the continuous phase can be formed so that they are stable over a wide temperature range and have intermediary properties between flexible and stiff microemulsions. Three components (1-ethyl-3-methylimidazolium ethylsulfate ([emim][etSO(4)]), limonene, and octylphenol ethoxylate (Triton X 100, abbreviated as TX-100)) were used. This ternary system has been characterized from ambient temperature down to -10 °C by means of conductivity, viscosity, and small-angle X-ray scattering (SAXS) measurements. The SAXS data exhibit a characteristic single, broad scattering peak in conjunction with a typical q(-4) decay at large q values. The SAXS data have also been interpreted in terms of a dimensionless dilution plot, demonstrating that microstructures are neither isolated droplets nor a random flexible film structure but resemble molten liquid crystals (i.e., they are formed from locally cylindrical or planar structures). This semirigidity is attributed to a good match between the surfactant and the ionic liquid; this holds in a temperature range well below 0 °C.
Abstract:We report on studies of an inorganic electrolyte: LiAlCl 4 in liquid sulfur dioxide. Concentrated solutions show a very high conductivity when compared with typical electrolytes for lithium ion batteries that are based on organic solvents. Our investigations include conductivity measurements and measurements of transference numbers via nuclear magnetic resonance (NMR) and by a classical direct method, Hittorf's method. For the use of Hittorf's method, it is necessary to measure the concentration of the electrolyte in a selected cell compartment before and after electrochemical polarization very precisely. This task was finally performed by potentiometric titration after hydrolysis of the salt. The Haven ratio was determined to estimate the association behavior of this very concentrated electrolyte solution. The measured unusually high transference number of the lithium cation of the studied most concentrated solution, a molten solvate LiAlCl 4 × 1.6SO 2 , makes this electrolyte a promising alternative for lithium ion cells with high power ability.
OPEN ACCESSEnergies 2013, 6 4449
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