Micelle Formation of Long-Chain Imidazolium Ionic Liquids in Aqueous Solution Measured by Isothermal Titration Microcalorimetry

Self-association of three long-chain imidazolium ionic liquids (ILs), [C(12)mim]Br, [C(14)mim]Br, and [C(16)mim]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 oil the critical micelle concentration (CMC) were examined. Thermodynamic parameters. Delta(mic)G, Delta H-mic, and Delta S-mic, 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 (Delta(mic)G, Delta H-mic, and Delta S-mic) were determined based on the isothermal titration microcalorimetry results. These CMC values are approximately equal to file CMCs obtained by surface tension measurement.