Combination of a protic ionic liquid-like surfactant and biocompatible solvents to generate environmentally friendly anionic reverse micelles

Abstract

In the present work we have formulated environmentally friendly anionic reverse micelles (RMs) by the combination of a protic ionic liquid-like surfactant with biocompatible nonpolar solvents. Thus, the protic ionic liquid, 1-methylimidazolium bis-(2-ethylhexyl)phosphate (imim–DEHP), water and isopropyl myristate (IPM) or methyl laurate (ML) were used as the surfactant and polar and nonpolar solvents, respectively. The ability of imim–DEHP to create RMs in both nonpolar solvents (IPM and ML) was evaluated by different techniques such as dynamic (DLS) and static (SLS) light scattering and FT-IR. The results obtained were compared with those of a system formed from sodium 1,4-bis-2-ethylhexylsulfosuccinate (Na-AOT) in the same biocompatible solvents in order to elucidate how the surfactant chemical structure affected the organized media generated. Our results show that imim–DEHP forms RMs in both nonpolar solvents but these systems are different (maximum amount of water dispersed and sizes) from the one formed using Na-AOT in the same external solvents. Strong water–surfactant interactions in imim–DEHP RMs produce changes in sizes and interfacial properties in greater magnitude than in Na-AOT RMs. Additionally, an opposite dependence on the water content and the type of external solvent was detected. Thus, the chemical structure of the protic surfactant dominates the interfacial behavior at low water content and, consequently, the external solvent does not seem to have any influence on them. In summary, we consider that our work introduces imim–DEHP as a very promising surfactant for future applications for nanoreactors and in nanotechnology.