IL-in-oil microemulsions

Scheme 10.3 Schematic representation of IL-in-oil microemulsion with drug molecule in the core. Reproduced from Moniruzzaman et al. [105], J. Colloid Interface Sci. 2010,352,136, with permission from Elsevier Science.

Recently, we have shown that ILs with long-chain alkylsulfates, that is, Bmim octylsulfate, BmimOctSO [18], and Bmim dodecylsulfate, BmimDodSO [19], can completely take over the role of the surfactant in the microemulsion formation process. This means nonaqueous, halogen-free microemulsions are formed by mixing two ILs with one oil component. In these systems, EmimEtSO is the polar component, and BmimOctSO or BmimDodSO fulfills the requirements of the interfacial film component. Conductivity measurements established by Gao et al. [8] can be successfully applied to detect the transition between the oil-in-IL and the bicontinu-ous as well as the bicontinuous and the IL-in-oil microemulsion. Figure 12.6 shows the corresponding phase diagram in the presence of BmimOctSO. ... 

An IL-in-oil microemulsion [98] can be formulated by using an l-octyl-3-methylimidazolium chloride, [Cgmim][Cl], as IL-S and [C mim][PFJ as a substitute for traditional organic solvent. DLS was used to confirm the formation of [C mim] [PFJ-in-water microemulsions with an average size of 3 nm. 

Recent studies [104, 105] have formulated IL-in-oil microemulsions by using IL-S obtained from combination of single- and two-tail anions with imidazolium... 

While the studies mentioned previously involve water as one of the component, water-free IL-based microemulsions are also studied by many groups [54,56-68]. In the first report on formation of IL-in-oil microemulsions, Gao et al. [57] prepared [C mim][BFJ/TX-100/cyclohexane microemulsions and characterized them by... 

This section has two parts in the first, we discuss the developed new strategy to prepare and characterize IL-in-oil microemulsions in the second, we discuss the ways to adjust the structural parameters of microemulsions using different ILs as additives (polar phase). 

To further support the formation of IL-in-oil microemulsion, we have utilized the typical polarity probe betaine 30 ( . (30) probe) [84-86]. For large negative solvato-chromism, the /Sj.(30) probe has been widely used by many groups to determine the polarity of different systems [84-90]. The absorption spectra of .j.(30) probe are shown in Rgure 15.2a, which clearly shows that the absorption maximum (2 )... 

The study presented here describes the formation and characterization of different IL-in-oil microemulsions containing an anionic SAIL, [C mim][AOT]. This work opens up the possibility of creating a large number of IL-in-oil microemulsions, just by replacing the inorganic cation, Na of NaAOT, by any organic cation and using different IL as the polar core. It clearly provides different ways to tune the structure... 

Han and coworkers [13] further studied the phase behavior of toluene/TX-100/1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF ]) system. As shown in Figure 16.2, the single-phase microemulsion area covers about 75% of the phase diagram at 25 °C. A transition from IL-in-oil microemulsion (marked as A) via a bicontinuous region (marked as B) to an oil-in-IL microemulsion (marked as C) occurs with the increase of weight fraction of TX-lOO and [bmim][PFJ. 

Figure 16.2 Phase diagram of toluene/TX-100/[bmim] [PFJ (in weight fraction) at 25.0 °C. A, IL-in-oil microemulsion B, bicontinuous region C, oil-in-IL microemulsion and D, biphasic region. Reproduced from Li et al. [13] with permission from Elsevier.

Sarkar and coworkers [17] reported the formulation of a IL-in-oil microemulsion, where the polar core of the IL, l-ethyl-3-methylimidazolium n-butylsulfate ([C mim] [C SO ]), is stabilized by a mixture of two nonionic surfactants, polyoxyethylene sor-bitan monooleate (IVeenSO) and sorbitan laurate (Span20), in a biocompatible oil phase of isopropyl myristate (IPM). The pseudoternary phase diagram of the [C mim] [C SO ]/l veen80/Span20/IPM microemulsion system is shown in Figure 16.6. 

Figure 17.7 (a) Schematic of IL-in-oil microemulsions used as a pharmaceutical carrier, (b) Chemical structure of IL and (c) acyclovir. Reproduced from Moniruzzaman et al. [44] with permission from Elsevier B.V. 

Nonaqueous IL microemulsions were also used as catalysts to improve reaction efficiency. Gayet et al. established an IL-in-oil microemulsion system with benzylpyridinium bis(trifluoromethanesulfonyl)imide ([BnPyrJNTfj), TX-lOO, and toluene, in which the Matsuda-Heck reaction between methoxybenzene diazotate and 2,3-dihydrofuran took place [46]. The reaction yield in this IL-in-oil microemulsion was twice as high as that in neat ILs. The results provided a basis for designing a nonaqueous IL microemulsion microreactor and also showed that nonaqueous IL microemulsion might have good prospects of applications in biocatalysis and nanomaterial synthesis. 

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