Results for Ionic Liquids

Since this is just the beginning of investigations into the diffusion behavior and intermolecular forces in ionic liquid systems, further experimental work needs to be done both with pure ionic liquids and with systems of mixtures of ionic and organic liquids. 

Tyrrell and K.R. Harris, Diffusion in Liquids, Butterworths, London, 1984. 

Cussler, Diffusion - Mass Transfer in Fluid Systems, Cambridge University Press, Cambridge, 1984. 

Thermodynamics of irreversible processes, Dover Publications, Mineola (NY), 1990. 

The Mathematics of Diffusion, 2nd ed., Clarendon Press, Oxford, 1975. 

Self-diffusion coefficients were measured with the NMR spin-echo method and mutual diffusion coefficients with digital image holography, respectively. As can be seen from Fig. 4.3-3, the diffusion coefficients show the whole bandwidth of diffusion coefficient values from 10 m s on the methanol-rich side down to 10 m s on the [BMIMjlPFej-rich side. The concentration dependence of the diffusion coefficients on the methanol-rich side is extreme and shows that special care and attention should be paid in the dimensioning of chemical processes with ionic liquids. 

Typical values of self-diffusion coefficients and mutual diffusion coefficients in aqueous solutions and in molten salt systems such as (K,Ag)N03 are of the order 

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We should expect similar results for ionic liquid simulations, and that greater accuracy will come with improved treatment of inter- and intramolecular energetics. Second, the simulations have yielded a tremendous amount of quantitative and qualitative information, which has enabled us to understand molten salt systems much better than would have been possible using only experiment or theory. We know that the Coulombic forces lead to order over a much longer length scale than is present in simple liquids [112] and that these forces can lead to the appearance of small voids having lifetimes on the order ofps[112,113]. This is in contrast to normal molecular liquids, where the steeply repulsive part of the potential dominates fluid structure and leads to a more close-packed structure. 

In summary, various approaches were developed and validated for ionic liquids over the last years. It was shown that dispersion corrected KS-DFT approaches allow reliable results for ionic liquids. " Recently, a comparison of trajectories obtained from ab initio molecular dynamics simulations with and without a dispersion correction revealed that the dynamics of the system is more accurately described for the dispersion corrected one, ° which highlights the necessity of dispersion corrected approaches in ab initio molecular dynamics simulations. Polarisable force fields were developed which allow the investigation of various ionic liquids.Cheaper nonpolarisable force fields are also available for a broad range of ionic liquids. However, the latter force fields tend to show too... 

Results for ionic liquids containing the l-R,3-methylimidazole cation (R = ethyl, butyl, and hexyl) and some common anions such as chloride, trifluoroacetate,... 

The polarity of some l-alkyl-3-methylimidazolium ionic liquids has been determined using the solvatochromic dyes Nile Red and Reichardt s dye [16, 17], Measurements with Nile Red do not give absolute values of polarity but provide a useful scale to estimate the relative polarity of the ionic liquids. Similar measurements have been made using a number of other solvatochromic dyes (dansylamide, pyrene, pyrenecarboxyaldehyde, and bromonapthalene) for [BMIM][PF6], and gave results consistent with those obtained with Nile Red. Values for Ej obtained for ionic liquids generally fall between the values of 0.6 and 1.0, as shown in Table 4.3. 

Application may be found for ionic liquids of resonance-stabilized methanides which can easily be prepared from the alkali salts. The first synthetic step includes the formation of the nearly insoluble silver salts in water (AgX, X = methanide). Since the silver salts dissolve in 2N aqueous NH3, adding ethyl(methyl)imidazolium bromide (EMHBr") results in the formation of a water-soluble ethyl(methyl)imidazolium methanide (EMHX") which can be separated from the AgBr precipitate by filtration. ... 

The exploration of novel types of ILs has involved important and intensive work. For the battery use, higher concentration of Li+ in the electrolyte is required and for this purpose the lithium salt itself hopefully could be melted at room temperature. Fujinami et al. have designed a novel bulky anion and demonstrated that certain kinds of Li salts can become viscous fluids at ambient temperature with a conductivity of between 10 and 10 S cm [31]. This result is still far from practical application and the electrochemical window is still unknown, but the work has shown unique progress for ionic liquids. 

Fig. 4 Schematic representation of the different atom-atom interactions parameterized in the CLAP force field for ionic liquids. The two bar graphs summarize the validation of the force field results (red bars) against molar density, pm, and molar enthalpy of vaporization, AHn, data (green bars). The standard deviations between the simulated and experimental sets are 8p = 3% and SAH = 30% —...

More exhaustive and theoretically based studies are required to rationalize the different trends and care is recommended when comparing or using viscosity data for ionic liquids as differences among the results of several authors may be important since, as it is well known, the presence of small amounts of water or other impurities such as chloride seem to have a remarkable effect on the viscosity [76-81],... 

At 100 °C no product was ever observed. At 150 °C the imidazolium-based ionic liquids could be prepared. For ionic liquids bearing pyridinium cations a reaction temperature of 200 °C was required. The reactions could be scaled up to 50 g and no large excess of alkyl halide was needed. Deetlefs and Seddon studied the synthesis of pyrazolium, thiazolium, imidazolium, and pyridine-based ionic liquids [21]. Selected results are summarized in Table 7.1. The authors reported that the reactions are up to 72 times faster than when using conventional heating. They also found that if the microwave irradiation is prolonged, decomposition of the ionic liquid occurs. Imidazolium halide based ionic liquids could be prepared in 150,... 

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