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Density and speed-of-sound data for 1-propyl-3-methylimidazolium bromide ([C 3 mim][Br]) + acetonitrile (MeCN), [C 3 mim][Br] + dimethylformamide (DMF), and [C 3 mim][Br] + dimethylsulfoxide (DMSO) binary mixtures in the dilute concentration region are reported at T = (288.15 to 308.15) K. From these data, apparent molar volume, isentropic compressibility, excess molar volume, and isentropic compressibility deviation values have been calculated. Negative deviations from the ideal behavior of both molar volume and isentropic compressibility have been observed for all systems investigated in this study. It has been found that deviations from ideal behavior for the [C 3 mim][Br] + MeCN system are larger than those for the [C 3 mim][Br] + DMF system which, in turn, are larger than those for the [C 3 mim][Br] + DMSO system. The results have been interpreted in terms of ion-dipole interactions and structural factors of the ionic liquid and investigated organic solvents.

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The vapor-liquid equilibria properties of sodium n-heptyl sulfonate (C 7 SO 3 Na) in pure water and in aqueous poly(ethylene glycol) (PEG) solutions were determined at different temperatures below and above the critical micelle concentration (CMC). Vapor-liquid equilibrium data such as water activity, vapor pressure, osmotic coefficient, activity coefficient and Gibbs free energies were obtained through isopiestic method. The concentration dependence of all investigated thermodynamic properties exhibit a change in slope at the concentration in which micelles are formed. It was found that the vapor pressure depression for a ternary aqueous C 7 SO 3 Na + PEG system is more than the sum of those for the corresponding binary solutions and, at higher temperatures, the higher concentration of PEG is in equilibrium with a certain concentration of surfactant.