Aggregation behavior of dodecylsulfonate-based surface active ionic liquids in water

Halogen-free, low-cost alkylsulfonate-based surface active ionic liquid (SAIL), 1-butyl-3-methylimidazolium dodecylsulfonate ([C 4 mim][C 12 H 25 SO 3 ]) was easily synthesized through ion exchange reaction . Its self-aggregation behavior was systematically investigated by surface tension and electric conductivity measurements. [C 4 mim][C 12 H 25 SO 3 ] has rather lower cmc than the traditional ionic surfactant , sodium dodecylsulfonate (SDDS), while it has higher cmc than the anionic SAIL, 1-butyl-3-methylimidazolium dodecylsulfate ([C 4 mim][C 12 H 25 SO 4 ]), with the same hydrocarbon chain length. The negative ΔG m θ values, mainly result from more negative −   T ΔS m θ , which demonstrates that the micellization process is spontaneous and entropy-driven in the temperature range investigated. Furthermore, influence of four organic electrolytes, viz. tetraalkylammonium bromides ((CH 3 ) 4 NBr, (C 2 H 5 ) 4 NBr, (C 3 H 7 ) 4 NBr, and (C 4 H 9 ) 4 NBr), on the aggregation behavior of [C 4 mim][C 12 H 25 SO 3 ] in aqueous solution was studied. The results show that all the electrolytes investigated promote aggregates formation of [C 4 mim][C 12 H 25 SO 3 ]. In addition, to comprehend the discrepancy in the surface activity of alkylsulfate- and alkylsulfonate-based SAILs, theoretical calculations were performed to evaluate the electrostatic potential of the corresponding anion. Compared to [C 4 mim][C 12 H 25 SO 4 ], the inferior surface activity of [C 4 mim][C 12 H 25 SO 3 ] mainly originates from the less electronegativity of its anion. This work illustrates the self-assembly of the environmentally friendly alkylsulfonate-based SAILs and is expected to be useful in the applications of ionic liquids.