Phase behavior of new aqueous two-phase systems: 1-Butyl-3-methylimidazolium tetrafluoroborate + anionic surfactants + water

Abstract

The aqueous mixtures of an anionic surfactant (sodium dodecyl benzene sulfonate, SDBS) and an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate, [Bmim]BF₄) within a certain range of compositions can spontaneously separate into two immiscible aqueous phases (ATPS): one surfactant-rich and the other ionic liquid-rich. The phase diagrams of the ternary system of the SDBS/[Bmim]BF₄/water were drawn based on experimental data determined at 10.0, 20.0 and 30.0 °C, respectively. The borderlines of the different specific regions in the diagrams were determined using turbidity titration method. The narrow two-phase region aqueous were found to be close to the water - [Bmim]BF₄ side. The formation conditions, compositions, and physicochemical properties of the aqueous two phases have been studied. The effects of temperature, surfactant and ionic liquid content on the phase separation time and phase volume ratio of the ATPS were also investigated. This phase separation phenomenon was found to be likely due to the existence of micelle aggregates with quite large size obtained by Transmission Electron Microscopy (TEM) and Steady-state Fluorescence Quenching Measurements (SFQM) methods.