Both ionic liquids and water are typical green solvents. In this work, the phase behavior of the ternary system consisting of ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6), TX-100, and water was determined at 25.0 degrees C. The water-in-bmimPF6, bicontinuous, and bmimPF6-in-water microregions of the microemulsions were identified by cyclic voltammetry method using potassium ferrocyanide K4Fe(CN)6 as the electroactive probe. Dynamic light scattering (DLS) and the UV-vis method were used to characterize the microemulsions. It was demonstrated that the hydrodynamic diameter (Dh) of the bmimPF6-in-water microemulsions is nearly independent of the water content but increases with increasing bmimPF6 content due to the swelling of the micelles by the ionic liquid. The UV-vis further confirmed the existence of water domains in the water-in-bmimPF6 microemulsions, and the salt potassium ferricyanide K3Fe(CN)6 could be dissolved in the water domains.

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Self-association of three long-chain imidazolium ionic liquids (ILs), [C12mim]Br, [C14mim]Br, and [C16mim]Br, in aqueous solution was studied by surface tension measurements over a temperature range from (278.15 to 328.15) K. Effects of temperature and hydrocarbon chain length of the three long-chain ILs on the critical micelle concentration (CMC) were examined. Thermodynamic parameters, Δmic G, Δmic H, and Δmic S, of micellization were determined by applying a mass-action model equation. Isothermal titration microcalorimetry was used to obtain the enthalpy change upon micellization of the three long-chain ILs at 298.15 K. Moreover, the CMCs and the thermodynamic parameters (Δmic G, Δmic H, and Δmic S) were determined based on the isothermal titration microcalorimetry results. These CMC values are approximately equal to the CMCs obtained by surface tension measurement.