Aggregation Behaviours of Surface-Active Ionic Liquids 1-Alkyl-3-methylimidazolium Bis(2-ethylhexyl)sulfosuccinate

The systematic investigation of the aggregation behaviours of newly synthesised surface-active ionic liquids 1-alkyl-3-methylimidazolium bis(2-ethylhexyl)sulfosuccinate ([C(n)mim][AOT], n = 2, 3, 5, 6, 7) by various techniques is reported. The critical aggregation concentrations (CACs) and the standard Gibbs free energies of aggregation (Delta G(m)(0)) were determined from measurements on conductivity, fluorescence, and surface tension, which suggested a stronger self-assembly ability in the bulk solution for [C(n)mim][AOT] surfactants with longer alkyl chain cations. An interesting structure transition driven by the penetration of the imidazolium cation into the aggregate when n > 4 was found by analysis of the variations of the values of CAC, Delta G(m)(0), the degree of counter ion binding (beta), and the micropolarity (I-1/I-3) immediately after the CAC with changing alkyl chain length of the imidazolium cation, which was further confirmed by H-1 NMR measurements.