Density and viscosity data for four 1-ethyl-3-methylimidazolium-based ionic liquids combined with alkyl sulfate, [C n SO 4 ] À with n = 1, 4, 6, and 8, and hydrogen sulfate, [HSO 4 ] À , anions were measured at atmospheric pressure in the temperature range 283 < T/K < 363. Isobaric thermal expansion coefficients were calculated from the density results. This work studies the effect of increasing the alkyl chain length of the sulfate-based anion on the density, viscosity, and related properties of this family of ionic liquids. The effective volumes of the distinct anions used were calculated from the measured density values, simply by subtracting the effective volume of the cation already available from literature to the molar volume of the ionic liquid. We also evaluated the predictive ability of group contribution methods for density and viscosity. Since large deviations between the predictions and the experimental data occurred for both density and viscosity, new group contribution parameters were proposed. The results clearly show that [HSO 4 ] À cannot be considered part of the [C n SO 4 ] À family. ' INTRODUCTIONIonic liquid (IL) research has boomed due to attractive properties common to several families of ILs, such as wide liquid range, nonflammability, and negligible vapor pressure at ambient conditions. 1À4 The potential development of reliable and economical process designs for industrial applications of ILs depends on the thorough knowledge of their most relevant thermophysical properties such as density, 5À7 viscosity, 8 and heat capacity. 9 Although the literature in this area has grown enormously in the past few years, every day new ILs are being synthesized. A careful analysis of the literature shows that the basic properties have only been measured for a limited number of ILs. The IL Thermo database contains no information regarding the density and viscosity data for the ILs used in this work, namely, [C 2 mim][C n SO 4 ] with n = 1, 4, 6, and 8 and [C 2 mim] [HSO 4 ]. However, for the more common [C 2 mim] [C 2 SO 4 ] several studies have been published.Generally, IL density varies between 0.85 g 3 cm À3 and 1.6 g 3 cm À3 , depending on the choice of both cation and anion; it then decreases as the alkyl side chain grows in a systematic way. 10 The viscosity of room temperature IL ranges from 10 cP to 10 5 cP, which is up to 3 orders of magnitude higher than that of conventional organic solvents. Such high viscosities are known to severely hinder possible industrial applications. Impurities such as water are important, since they dramatically reduce the IL viscosity. 11 Commonly, the increase of the alkyl chain length of the [C n mim] + cation increases the viscosity due to an increase in the van der Waals interaction domains. 8 Although considerable data exist relating to the influence of increasing the alkyl side chain in alkyl-imidazolium based ILs, few systematic studies have appeared on the same effect in the anion. In fact, there are few anions where this effect can be evaluated. One such ...

Density and viscosity data of the N-alkyl-N,N-dimethyl-N-(2-hydroxyethyl)ammonium bis(trifluoromethylsulfonyl)imide ionic liquids homologous series [N(1 1 n 2(OH))][Ntf(2)] with n=1, 2, 3, 4 and 5 have been measured at atmospheric pressure in the 283

The liquid-liquid equilibria of mixtures of cholinum-based ionic liquids (N-alkyl-N,N-dimethylhydroxyethylammonium bis(trifluoromethane)sulfonylimide, [N(11n2OH)][Ntf(2)], n = 1, 2, 3, 4, and 5) plus water or 1-octanol were investigated at atmospheric pressure over the entire composition range. The experiments were conducted between 265 and 385 K using the cloud-point method. The systems exhibit phase diagrams consistent with the existence of upper critical solution temperatures. The solubility of [N(1 1 n 2OH)][Ntf(2)] in water is lower for cations with longer alkyl side chains (larger n values). The corresponding trend in the octanol mixtures is reversed. The ([N(1 1 1 2OH)][Ntf(2)] + water + octanol) ternary system shows triple liquid-liquid immiscibility at room temperature and atmospheric pressure. A combined analytic/synthetic method was used to estimate the corresponding phase diagram under those conditions. Auxiliary molecular dynamics simulation data were used to interpret the experimental results at a molecular level.

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The aim of this work is to understand the details of the interactions of ionic liquids with carbon nanomaterials (graphene and nanotubes) using polyaromatic compounds as model solutes. We have combined the measurements of thermodynamic quantities of solvation with molecular dynamics simulations to provide a microscopic view. The solubility of five polycyclic aromatic hydrocarbons (naphthalene, anthracene, phenanthrene, pyrene and coronene) was determined in seven ionic liquids ([CCim][C(CN)], [CCpyrr][Ntf], [CCim][Ntf], [CCim][C(CN)], [CCim][Ntf], [CCpyrr][N(CN)] and [CCim][N(CN)]) at 298 K. The enthalpies of the dissolution of naphthalene, anthracene and pyrene were measured in four of the ionic liquids. Free energies were estimated from those measurements in order to analyse the entropic or enthalpic contributions to the dissolution process. Molecular dynamics simulations provided solvation free energies that were compared to experimental and structural information. Spatial distributions of solvent ions around the solutes when combined with IR measurements elucidate the structure of solvation environments. Interactions between the imidazolium rings of cations and the π system of the solutes have been identified. However, ionic liquids with pyrrolidinium cations appeared as better solvents due to favourable enthalpic contributions compared to imidazolium cations. Long alkyl side chains on cations lead to higher solubility and lower enthalpy of dissolution by creating a "softer" solvation environment. Considering the effect of anions, small and planar anions lead to higher solubilities and lower enthalpies of dissolution of polyaromatic hydrocarbons. These findings provide the design principles based on molecular interactions and the structure of solvation environments to choose or formulate ionic liquids in view of their affinity for carbon nanomaterials.