IL/O microemulsions

Figure 17.3 A schematic representation of water molecules in two different microenvironments. (a) IL/0 microemulsion without IL pools (b) IL/O microemulsion with an IL pool. Reproduced from Gao et al. [14] with permission from Wiley.

DLS was used to obtain the hydrodynamic diameter of dispersed droplets in the microemulsion [38], To investigate the effect of alkyl chain length of IL on the physicochemical properties of microemulsions, ternary microemulsion systems of [C2mim][C SO ]/TX-100/cyclohexane (n of C SO 4-6) were investigated by DLS at 298 K. DLS measurements showed that the hydrodynamic diameter of IL/O microemulsion increased linearly with the increasing molar ratio of water to the total surfactant and the hydrodynamic diameter also increased with alkyl chain length of the IL, as shown in Figure 18.5 [42]. 

In the IL/O microemulsion, a constant polarity of the IL pool was observed after adding small amounts of water to the microemulsion [43], suggesting that the water... 

The formation of IL/O microemulsions in mixtures of [bmim][BFJ (IL) and cyclohexane, stabilized by the nonionic surfactant, TX-lOO has been proved [30]. Three-component mixtures could form IL/O microemulsions of well-defined droplet size determined by fixing the water content (mole ratio of IL to TX-lOO) [30,48,49]. An upper critical point (T) was observed in the mixture [([bmim][BFJ/ TX-lOO)-I-cyclohexane] with fixed water content (mole ratio of [bmim][BFJ to TX-lOO) [50]. The mixture separated into two microemulsion phases of different composition but with the same composition below as occurred in other systems [48]. The microemulsion system, [bmim][BF ]/TX-100 +cyclohexane, could be regarded as a pseudobinary mixture of [bmim][BF ]/TX-100 IL droplets dispersed in the cyclohexane continuous phase. Therefore, the phase behavior could be depicted in a two-dimensional diagram with concentration of droplets along the abscissa and temperature along the ordinate. A coexistence curve of temperature (T) against a concentration variable, such as volume fraction ( ), could then be drawn in the same way as it was done for pseudobinary mixtures in AOT/water/decane micro-emulsions [48]. 

Figure 18.15 Schematic representation of ionic hqnid-in-oil (IL/O) microemulsions containing drug molecules. Reproduced from Moniruzzaman et al. [45] with permission from Academic Press Inc. Elsevier Science.

The growing interest on IL/O microemulsions is evident from the publication of many reviews in the last few years [9, 95-100]. Although the structural properties and applications were discussed extensively in these articles, the dynamical behavior of these novel systems was meagerly reviewed. In this chapter, we review some aspects of these microemulsions, with an emphasis on structural characteristics and solvation dynamics of the confined IL pool. 

The confinement and microviscosity of the IL pool in IL/O microemulsions can have profound effects on its molecnlar dynamics. Time-resolved anisotropy measurements provide useful information on dynamics by monitoring the rotational relaxation of an excited dye molecule, such as coumarin-based fluorophores. Time-resolved fluorescence anisotropy can be calcnlated using Equation 19.1 ... 

Sustainable and controlled syntheses of polymers and polyelectrolyte membranes have been carried out in IL/O microemulsions, where the corresponding monomeric organic compounds constitute the oil phase. For example, Yan and coworkers used MMA/[Cj2mim][Cl]/[bmim][BFJ microemulsion to carry out atom transfer radical polymerization (ATRP) reaction to generate polymethyl methacrylate (PMMA) [133]. When this reaction was carried out in conventional microemulsions, large quantity of surfactants was needed to stabilize these systems, which rendered the... 

A good example was brought by Moniruzzaman et al. which have used ionic liquid-in-oil (IL/o) microemulsions to enhance the topical and transdermal delivery of acyclovir (ACV). The microemulsion was composed by a blend of nonionic surfactants, namely polyoxyethylene sorbitan monooleate (Tween-80) and sorbitan laurate (Span-20), isopropyl myristate (IPM) as an oil phase, and IL [Cimim](CH30)2P02 (dimethylimidazolium dimethylphosphate) as a pseudophase. The solubility of ACV on the microemulsion system significatively increased in the presence of IL, which act as a drug reservoir during the process of delivery. Moreover the transdermal delivery was only achieved when the IL was present in the microemulsion mixture. 

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