The densities and viscosities for mixtures of 1-n-butyl-3-methylimidazolium tetrafluoroborate ionic liquid with acetonitrile, dichloromethane, 2-butanone and N,N-dimethylformamide have been determined at 298.15 K. From these measurements, it was found that viscosities of the mixtures can generally be described by an exponential equation. Their densities are linear functions of the mass fraction of the ionic liquid in the mixtures. These physical properties can be predicted as a function of the concentration of ionic liquid provided that the properties for pure components are known. The excess molar volume V E m and the excess logarithm viscosities (ln h) E were calculated and fitted to the Redlich-Kister polynomials. It is shown that the values of V E m are negative but those of (ln h) E are positive. Surprisingly, the minimum in V E m and the maximum in (ln h) E are observed at about the same mole fraction of the ionic liquid, x ≈ 0.3. The results are discussed in terms of the ion-dipole interactions between the cations of the ionic liquid and the organic solutes.

Densities, conductivities, and polarity indexes of pyrene for aqueous solutions of a series of ionic liquids [C(n)mim]Br (n = 4, 6, 8, 10, 12) and [C4mim][BF4] have been determined at 298.15 K as a function of ionic liquid concentrations. It was shown that possible aggregation appeared for the ionic liquids in aqueous solutions except for [C4mim]Br. The critical aggregation concentration (CAC) of the ionic liquids, the ionization degree of aggregates (beta), the standard Gibbs energy of aggregation (Delta G(m)(o)), the limiting molar conductivity (Lambda(m)(o)), and the standard partial molar volume (V(m)(o)) for the ionic liquids were derived from the experimental data. The dependence of the CAC, Delta G(m)(o), Lambda(m)(o), and V(m)(o) on the length of the alkyl chain of the cations was examined. It was further suggested from volumetric data that a micelle was formed for [C8mim]Br, [C10mim]Br, and [C12mim]Br in aqueous solutions. Their apparent molar volumes at the critical micelle concentration (V Phi,CMC), apparent molar volumes in the micelle phase (V(Phi)(mic)), and the change of their apparent molar volume upon micellization (Delta V Phi,m) were calculated by application of the pseudophase model of micellization. In addition, the average aggregation number of [C(n)mim]Br (n = 8, 10, 12) has been determined by the steady-state fluorescence quenching technique, and predicted from a simple geometrical mode. It is found that the experimental values are in good agreement with the predicted ones.

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Liquid−liquid equilibrium data have been determined for imidazolium ionic liquid ([C4mim]Cl, [C6mim]Cl, [C4mim]Br, [C6mim]Br, [C8mim]Br, [C10mim]Br) + salt (KOH, K2HPO4, K2CO3, K3PO4) aqueous biphasic systems at T = 298.15 K, and in part at T = (308.15 to 318.15) K. Factors affecting the binodal curves such as nature of ionic liquids and salts and temperature are also studied. The binodal curves are fitted to a three-parameter equation, and the tie-lines were described by the Othmer−Tobias and Bancroft equations. It is found that an increase in temperature caused no significant expansion of the two-phase area. However, the binodal curves became more close to the origin with an increase in alkyl chain length of the ionic liquids (ILs), and the ionic liquids with the Br- anion are easier to form two phases compared to those with the Cl- anion. These data are expected to be useful for the development and design of the extraction process using ILs based on aqueous biphasic systems.