Imim-DEHP reverse micelles investigated with two molecular probes reveals how are the interfacial properties and the coordination behavior of the surfactant

Abstract

Aqueous reverse micelles (RMs) generated with the ionic liquid (IL)-surfactant 1-methylimidazolium bis-(2-ethylhexyl)phosphate (imim-DEHP) and the biocompatible solvents methyl laurate (ML) and isopropyl myristate (IPM) were studied through the use of two molecular probes: the IL 3,6-bis(dimethylamino) acridinium bis-(2-ethylhexyl) phosphate (AOBH-DEHP) and the complex N,N,N′,N′-tetramethylethylenediamine copper(II)acetylacetonate tetraphenylborate ([Cu(acac)(tmen)][B(C6H5)4]). The techniques used were absorption and emission spectroscopy. Specifically, we explore how the chemical nature of the surfactant alters RMs properties such as micropolarity, specific interactions, and restricted motion environment. Furthermore, we analyzed how the imim-DEHP assembly affects the coordination behavior of the surfactant. The results show that the interfacial properties of the imim-DEHP RMs are dominated by the chemical nature of the surfactant as a consequence of a strong interaction of the imim+ cation with water molecules. Because of this strong interaction imim+-water, the anion DEHP− has an enhanced capacity to coordinate ion Cu+2 in comparison when the surfactant is in a homogeneous medium. Also, our results demonstrate that the strength of the anion DEHP− as a ligand in imim-DEHP RMs can be modulated both through the choice of the external solvent and the water content. In summary, the obtained results are very interesting for the potential use of the imim-DEHP RMs as nanoreactors and in metals extraction.