Ionic Liquid-based Surfactants: A Step Forward
Ionic liquid-based surfactants are a group of ionic liquid derivatives capable of forming micellar aggregates when dissolved in water above a certain concentration, known as the critical micelle concentration (CMC). This new class of surfactants was initially obtained by incorporating long alkyl chain substituents within the charged cationic group of conventional monocationic IL structures. More recently, dicationic, tricationic, and functionalized IL-based surfactants have been described. IL-based surfactants present great tuneability as original ILs: simple modifications in their structures produce important variations in their micellar properties. Furthermore, micelles formed by IL-based surfactants exhibit lower CMC values than conventional cationic surfactants when comparing similar structures. It is important to characterize the micellization and interfacial behaviour of IL-based surfactants in order to apply them successfully in specific fields. Several techniques can be used for such characterization, such as surface tension, fluorescence and conductivity measurements. Due to their structural versatility and singular properties, IL-based surfactants have generated a great deal of interest, which is reflected in the increasing number of applications that have been reported in recent years. Among the main applications of IL-based surfactants, worthy of mention are biomedicine, catalysis, solvents, nanotechnology, and separation science fields.