Synthesis of trisiloxane-tailed surface active ionic liquids and their aggregation behavior in aqueous solution

The aggregation behavior of two trisiloxane-tailed surface active ionic liquids (ILs), 1-methyl-3- trisiloxaneimidazolium chloride ([Si(3)Mim]Cl) and trisiloxanepyridinium chloride ([Si(3)Py]Cl), in aqueous solution was investigated by the measurement of surface tension, electrical conductivity, transmission electron microscopy (TEM), dynamic light scattering (DLS), and X-ray diffraction (XRD). The surface tension measurement showed the critical aggregation concentration (cac) of [Si(3)Mim]Cl and [Si(3)Py]Cl is 15.5 and 24.8 mmol l−1 respectively, and the corresponding surface tension at cac (γcac) is 23.8 and 23.0 mN m−1, respectively. The phenomenon was mainly ascribed to the branched trisiloxane hydrophobic moieties and these results demonstrated that the surface activity of these trisiloxane-tailed ILs was somewhat superior to that of conventional ILs. The vesicular-like structure of the aggregates was observed by TEM while DLS provided the diameter distribution of these aggregates. In addition, a probable two-layered arrangement of molecules in aggregates for the two ILs in aqueous solution was proposed based upon the results of XRD studies. This investigation may contribute to expand understanding of trisiloxane-tailed ILs. Furthermore, high thermal stability of such compounds may improve their potential applications in the fields of colloids and interfaces science.