Self-Assembled CTAB Nanostructures in Aqueous/Ionic Liquid Systems: Effects of Hydrogen Bonding

Aggregation behavior of a conventional cationic surfactant, n-hexadecyl-trimethylammonium bromide (CTAB), in three imidazolium-based ionic liquids, N-butyl imidazolium chloride (N-BImCl), 1-butyl-3-methyl imidazolium chloride (BMImCl) and 1-hexyl-3-methyl imidazolium bromide (HMImBr)/water systems was investigated by tensiometry, fluorescence, H-1 NMR spectroscopy and dynamic light scattering (DLS). Different physicochemical properties such as the critical micelle concentration (CMC), interfacial properties, aggregate size, and polydispersity were determined. Just like in aqueous medium, micelles formed and CMC values were found to be larger in ionic aqueous/liquids (IL) than in water. The results revealed that the surface activity is much lower in aqueous/IL than in water. The types of anion and alkyl substitutions on the imidazolium ring were shown to be affecting the aggregation behavior. The variation of chemical shifts in the presence of surfactant revealed that the hydrogen bonding is an important factor in defining the solvent properties of ionic liquids since the structure of their hydrogen bond network which depends on their molecular structure has a prominent influence on solubility and the CMC of surfactants. It is demonstrated that HMImBr can be incorporated in CTAB micelles and form mixed micelles, but N-BImCl behaves partly as a solvent toward alerting the physicochemical properties of CTAB.