IL-based nonaqueous microemulsions

ILs are different from the conventional water solvent, as they consist of cations and anions, and thus, the structure and properties of IL-based nonaqueous microemulsions are unlike those of aqueous microemulsions. In this chapter, we outline recent advances in IL-based nonaqueous microemulsions, with a focus on the structure and properties of these systems. 

Zheng et al. reported a [bmim]BFyTX-100/toluene microemulsion system that was similar to the IL-based nonaqueous microemulsions mentioned earlier [10]. Cyclic voltammetry experiments were successfully introduced to verify the identification of microregions, in addition to conductivity measurements. 

Nonionic surfactants such as TX-lOO, polyoxyethylene sorbitan monooleate (Tween-80), or anionic sodium bis(2-ethyUiexyl) sulfosuccinate (AOT) are generally regarded as essential components in the formulation of microemulsions. Nevertheless, very recently, Xu et al. made remarkable progress in the development of novel IL-based nonaqueous microemulsions by producing a siufactant-free IL-based nonaqueous microemulsion for the first time [13]. The microemulsion consisted of [bmim]BF, ethanol, and toluene, without the involvement of any traditional surfactants. The phase behavior of the [bmim]BFyethanol/toluene system was similar to... 

As described previously, most IL-based nonaqueous microemulsions consist of a hydrophilic IL, a surfactant, and a nonpolar solvent. Although these microemulsions have been successfully constructed and applied to different fields, the problem of volatility of the environmentally unfriendly organic solvents cannot be avoided. One strategy, to replace both the internal (dispersed) and external (continuous) phases with two immiscible ILs, is theoretically possible, but it may not be easy to find two immiscible ILs because all the ILs are organic salts. 

IL-based nonaqueous microemulsion can also be used for preparation of silicon materials with different morphologies. By optimizing catalytic conditions, Zhao et al. synthesized two different morphologies of silica products using nonaqueous IL microemulsion ([bmim]BF -nTX-100-Hbenzene system) droplets as templates [45]. 

The applications of ILs are broadening with the advent of IL-based microemulsions. The IL-based nonaqueous microemulsions, particularly the IL/O ternary systems, have been considerably studied and subsequently used in industries. This class of mieroemulsion systems offers several advantages over the corresponding water-in-oil systems, due to the tunable size of the polar droplets, their wide range of temperature stability, and the ease of preparation for specific tasks. 

Compared to the many different types of ILs that have developed so far, a limited variety of those ILs are nsed in nonaqueous microemnlsions, and most of them are imidazohnm-based ILs. Among others, l-butyl-3-methyhmidazohum tetrafluorob-orate ([bmimJBF has been extensively used in many mieroemulsion studies since the pioneering work on IL-based microemulsions by Han et al. [5] probably, it is one of the most classical ILs to date. As a result, studies on [bmim]BF -based nonaqueous microemulsions are better characterized than those on other IL-based microemulsions. 

Zheng et al. investigated how organic solvents (cyclohexane, p-xylene, toluene, and benzene) worked in the formation of [bmimjBF -based oil-in-IL nonaqueous microemulsion systems [12]. The added molecular solvents provided a nonpolar environment that resulted in the aggregation of the hydrophobic tails of the surfactant TX-lOO, so that the molecular solvents formed droplets dispersed in the continuous [bmim]BF phase. Results of 2D H-NMR confirmed that the solvophobic interaction between the molecular solvents and the hydrophobic tails of TX-lOO was the driving force in the formation of those oil-in-IL microemulsions. 

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