Biocompatible Solvents and Ionic Liquid-Based Surfactants as Sustainable Components to Formulate Environmentally Friendly Organized Systems

In this review, we deal with the formation and application of biocompatible water-in-oil microemulsions commonly known as reverse micelles (RMs). These RMs are extremely important to facilitate the dissolution of hydrophilic and hydrophobic compounds for biocompatibility in applications in drug delivery, food science, and nanomedicine. The combination of two wisely chosen types of compounds such as biocompatible non-polar solvents and ionic liquids (ILs) with amphiphilic character (surface-active ionic liquids, SAILs) can be used to generate organized systems that perfectly align with the Green Chemistry concepts. Thus, we describe the current state of SAILs (protic and aprotic) to prepare RMs using non-polar but safe solvents such as esters derived from fatty acids, among others. Moreover, the use of the biocompatible solvents as the external phase in RMs and microemulsions/nanoemulsions with the other commonly used biocompatible surfactants is detailed showing the diversity of preparations and important applications. As shown by multiple examples, the properties of the RMs can be modified by changes in the type of surfactant and/or external solvents but a key fact to note is that all these modifications generate novel systems with dissimilar properties. These interesting properties cannot be anticipated or extrapolated, and deep analysis is always required. Finally, the works presented provide valuable information about the use of biocompatible RMs, making them a green and promising alternative toward efficient and sustainable chemistry.

Phase Behavior and Solubilization of Microemulsions Containing C16mimBr with Different Oil-Water Ratios

The effects of oil-water ratios (α) on the composition of the balanced interfacial layer and the optimum solubilization of microemulsions C16mimBr/butan-1-ol/oil (octane, decane, dodecane)/5% NaCl solution were investigated. As α increases, the alcohol solubility in water and oil phases (Sa) in the microemulsions also tends to increase. The reason is the relatively high solubility of the alcohol in the oil phase compared to the solubility in water. When α increases, the number of surfactant ( n s s ${\rm{n}}_{\rm{s}}^{\rm{s}}$ ) and co-surfactant ( n a s ${\rm{n}}_{\rm{a}}^{\rm{s}}$ ) molecules required to balance the interface layer and the proportion of alcohol in the interfacial layer (AS) increase but the solubilization capacity (SP*) decreases. When the total mass of water and oil is unchanged, the solubilization capacity of the microemulsion systems is lower the higher the relative content of oil is. The effects of different oils, salinity and temperature on the composition of the balanced interfacial layer and the solubilization of microemulsions were also investigated.