Interfacial properties modulated by the water confinement in Reverse Micelles created by the Ionic Liquid-like surfactant bmim-AOT.

LEPORI, CRISTIAN M. O.; CORREA, N. MARIANO MARIANO; SILBER, JUANA J.; VACA CHAVEZ, FABIAN; FALCONE, R. DARIO

SOFT MATTER

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2019 vol. 15 p. 947 - 955

1744-683X

The behavior of the interfacial water entrapped in reverse micelles (RMs) formed by the ionic liquid-like surfactant 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (bmim-AOT) was investigated by using UV-Vis absorption spectroscopy and nuclear magnetic resonance (NMR) relaxometry. The solvatochromism of two molecular probes: 1-methyl-8-oxyquinolinium betaine (QB) and N,N,N?,N?-tetramethylethylenediamine copper (II) acetylacetonate tetraphenylborate, ([Cu(acac)(tmen)][B(C6H5)4]) was followed. As a comparison, the analog RMs formed by sodium 1,4-bis-2-ethylhexylsulfosuccinate (Na-AOT) was also explored. By varying the water content inside the RMs and consequently the different magnitude in the water-surfactant interactions at the interface, interesting facts are 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 present smaller electron donor capacity than those in Na-AOT RMs. QB reveals that the interfacial region is less hydrogen bond donor and less polar than the corresponding for Na-AOT RMs. The NMR experiments show that the molecular motion of water in bmim-AOT RMs is less restricted than those water molecules confined in Na-AOT RMs. In summary, the results show how the nature of the bmim+ cation impact on 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.