Ionic liquid based microemulsions: A review

Over the past few years an increasing number of studies dealt with microemulsions, in which either the aqueous phase, the oil phase, the surfactant or even two of these components constitute of an ionic liquid. Many examples demonstrated that water and oil are not necessarily the required polar and non-polar components that contribute to the formation of microemulsions but can be replaced by targeted ionic liquids. Moreover, in many cases ionic liquids are used as amphiphiles that assist in the formation of microemulsions in aqueous or non-aqueous media due to their unique surface activity. In the present review, we highlight the properties of three types of ionic liquid based microemulsions, namely non-aqueous ionic liquid microemulsions, aqueous ionic liquid microemulsions and ionic liquid/oil/water microemulsions. Various characterization techniques applied for the confirmation of their formation and the detailed elucidation of their properties are discussed herein. Additionally, we present a comprehensive summary of the recent applications of ionic liquid based microemulsions in different fields, such as synthesis, (bio-)catalysis, polymerization, (nano-)material preparation, drug delivery and separations. (C) 2019 Published by Elsevier B.V.