(553g) Nonaqueous Microemulsions Containing Ionic Liquid and Polar Organic Solvent As the Polar Phase

Microemulsions are isotropic and thermodynamic stable mixtures of two immiscible solvents stabilized by surfactants. The majority of microemulsions studies use water as the polar component. However, attempts have been made to prepare and study nonaqueous microemulsions. Recently, using ionic liquids (ILs) instead of water to prepare nonaqueous microemulsions is an active subject. In current studies, the ILs mostly used are room-temperature ILs, or ILs with relatively small viscosity. Considering of the generally high viscosity of IL, and some even solids at room temperature, the broader use of ILs to form nonaqueous microemulsions are limited. In our research, in order to overcome this problem, polar solvent was used to dissolve or dilute ILs and then form microemulsions containing IL and polar solvent as the polar phase.

In this work, the IL 1-butyl-3-methylimidazolium chloride (bmimCl) was selected as a model IL. The polar solvent formamide (FA) was used to dissolve bmimCl, and the solution was used to form nonaqueous microemulsions in cyclohexane by the aid of surfactant TX-100. The phase behavior of this system at 25 ± 0.1 °C was studied. Electrical conductivity measurement was used to identify the microstructures of the nonaqueous microemulsions. Based on the phase diagram, the reverse microemulsions containing bmimCl-FA as the polar internal phase were investigated by the dynamic light scattering (DLS) and UV-Vis spectroscopy. DLS studies confirmed the formation of reverse microemulsions of bmimCl−FA in cyclohexane. The polarity of the polar domains in these reverse microemulsions was investigated by UV-Vis spectroscopy using methyl orange (MO) and methylene blue (MB) as absorption probes. UV-Vis studies using CoCl₂ as probe also indicated that the nonaqueous reverse microemulsions can dissolve metal salt. These nonaqueous reverse microemulsions with the solution of IL and polar organic solvent as the polar phase may have advantages in tuning the properties of the polar microenvironment by altering the IL or polar solvent.