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Interfacial properties modulated by the water confinement in reverse micelles created by the ionic liquid-like surfactant bmim-AOT

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Abstract

The behavior of the interfacial water entrapped in reverse micelles (RMs) that were formed by the ionic liquid-like surfactant 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (bmim-AOT) was investigated with the use of UV-Vis absorption spectroscopy and nuclear magnetic resonance (NMR) relaxometry. The solvatochromism of two molecular probes, namely, 1-methyl-8-oxyquinolinium betaine (QB) and N,N,N′,N′-tetramethylethylenediamine copper(II)acetylacetonate tetraphenylborate ([Cu(acac)(tmen)][B(C6H5)4]), was investigated. As a comparison, the analog RMs formed by sodium 1,4-bis-2-ethylhexylsulfosuccinate (Na-AOT) were also explored. By varying the water content inside the RMs and consequently the different magnitude of the water–surfactant interactions at the interface, interesting properties were observed by comparing bmim-AOT and Na-AOT RMs. From the solvatochromic behavior of ([Cu(acac)(tmen)][B(C6H5)4]), we found that the interface in bmim-AOT RMs shows a smaller electron donating capacity than that in Na-AOT RMs. QB revealed that the interfacial region is a weaker hydrogen bond donor and less polar than the corresponding Na-AOT RMs. NMR experiments showed that the molecular motion of water in bmim-AOT RMs is less restricted than that of the water molecules confined in Na-AOT RMs. In summary, the results show how the nature of the bmim+ cation affects the interaction between the entrapped water and the RM interface, greatly modifying the interfacial water structure in comparison with the results known for Na-AOT.

Graphical abstract: Interfacial properties modulated by the water confinement in reverse micelles created by the ionic liquid-like surfactant bmim-AOT

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Publication details

The article was received on 30 Oct 2018, accepted on 27 Dec 2018 and first published on 27 Dec 2018


Article type: Paper
DOI: 10.1039/C8SM02217H
Citation: Soft Matter, 2019, Advance Article
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    Interfacial properties modulated by the water confinement in reverse micelles created by the ionic liquid-like surfactant bmim-AOT

    C. M. O. Lépori, N. M. Correa, J. J. Silber, F. Vaca Chávez and R. D. Falcone, Soft Matter, 2019, Advance Article , DOI: 10.1039/C8SM02217H

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