Properties of Ionic Liquid‐Based Microemulsions

Ionic liquids are a new class of promising solvents that can be used in the formulation of microemulsions. They can be mainly used in three different ways: (i) as disperse medium by replacing water, (ii) as continuous medium by replacing alkane solvents, and (iii) as a surfactant in those situations where the ionic liquid self-aggregates. For cases (i) and (ii), the ionic liquid prototypes are imidazolium ones ([C4mim][BF4] and [C4mim][PF6]) as substitutes of water and oil, respectively. Nonionic surfactants (TX-100, Brij, and Tween) are the most frequently used. Recently, cationic surfactants have been used, and in this case, the anion exchange between the surfactant and the ionic liquids should be taken into consideration. The interaction between the oxyethylene groups of the nonionic surfactants and the imidazolium cation is responsible for its penetration at the interface of the microemulsion. Ionic liquids with both hydrophobic and hydrophilic domains can aggregate in a similar way to conventional surfactants. A third ionic liquid microemulsion category is formed by this kind of surfactants.