Micellar transitions in the aqueous solutions of a surfactant-like ionic liquid: 1-butyl-3-methylimidazolium octylsulfate

• Published in: Physical chemistry chemical physics : PCCP Vol. 12; no. 37; pp. 11728 - 11735
• Main Authors: Singh, Tejwant, Drechsler, Markus, Müeller, Axel H. E, Mukhopadhyay, I, Kumar, Arvind
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 01.01.2010
• Subjects: Alkanesulfonic Acids - chemistry; Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Imidazoles - chemistry; Ionic Liquids - chemistry; Micelles; Micelles. Thin films; Water - chemistry; Conductivity; Mixed micelle; Micelle; NMR spectrometry; Surfactant; Physical properties; Ionic liquid; Aggregation; Transmission electron microscopy; Electrolyte; Alkyl; Counter ion; Aqueous solution; Aggregate; Structure
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c003855p

We have observed dual transitions in various physical properties while investigating the surfactant-like behavior of the ionic liquid (IL) 1-butyl-3-methylimidazolium octylsulfate [C 4 mim][C 8 SO 4 ] in aqueous media. Interestingly, in conductivity measurements, it was found that the second transition, which is comparatively weak in pure water, can be modulated and tuned to the desired concentration without affecting the first transition by the addition of a suitable electrolyte. Using an array of techniques, such as conductivity, ultrasonics, TEM, cryo-TEM, DLS, 1 H NMR and 2D 1 H- 1 H NOESY, it has been revealed that the first transition corresponds to the anionic aggregation with imidazolium cations adsorbed as counterions, and the second transition corresponds to the restructuring of the initially formed aggregates in a way that the alkyl chain of the imidazolium cation is incorporated towards the micellar core, leading to a unique mixed micelle-type structure in a single IL system. Dual micellar transitions in aqueous solutions of the surfactant-like ionic liquid 1-butyl-3-methylimidazolium octylsulfate [C 4 mim][C 8 SO 4 ] have been observed and characterized.