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

LÉPORI, CRISTIAN M. O.; CORREA, N. MARIANO; SILBER, JUANA J.; VACA CHÁVEZ, FABIÁN; FALCONE, R. DARÍO

SOFT MATTER

ROYAL SOC CHEMISTRY

Año: 2019 vol. 15 p. 947 - 955

1744-683X

The behavior of the interfacial water entrapped in reverse micelles (RMs) that were formed by the ionicliquid-like surfactant 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (bmim-AOT) wasinvestigated with the use of UV-Vis absorption spectroscopy and nuclear magnetic resonance (NMR)relaxometry. The solvatochromism of two molecular probes, namely, 1-methyl-8-oxyquinoliniumbetaine (QB) and N,N,N0 ,N0-tetramethylethylenediamine copper(II)acetylacetonate tetraphenylborate([Cu(acac)(tmen)][B(C6H5)4]), was investigated. As a comparison, the analog RMs formed by sodium1,4-bis-2-ethylhexylsulfosuccinate (Na-AOT) were also explored. By varying the water content inside theRMs 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 thesolvatochromic behavior of ([Cu(acac)(tmen)][B(C6H5)4]), we found that the interface in bmim-AOT RMsshows a smaller electron donating capacity than that in Na-AOT RMs. QB revealed that the interfacialregion is a weaker hydrogen bond donor and less polar than the corresponding Na-AOT RMs. NMRexperiments showed that the molecular motion of water in bmim-AOT RMs is less restricted than thatof the water molecules confined in Na-AOT RMs. In summary, the results show how the nature of thebmim+ cation affects the interaction between the entrapped water and the RM interface, greatlymodifying the interfacial water structure in comparison with the results known for Na-AOT.