Phase and self-assembly transition induced by glycerol–borax interaction in an aqueous surfactant two-phase system†

We report that the phase and self-assembly transition in an aqueous surfactant two-phase (ASTP) system can be induced by a small amount of glycerol. The ASTP was formed from a cationic Gemini surfactant, C12C6C12(Et), and an anionic surfactant, sodium laureate (SL), in a borax solution. Upon addition of 0.3–2 vol% glycerol to the system, the ASTP system underwent a striking phase transition: three phases at 0.3–0.5% glycerol, a single birefringent phase at 0.7–1.2% glycerol, then again two phases, with the upper one like ice-cream. FF-TEM, CSLM and polarized microscopy revealed that the lamellae in the original upper phase were transformed into multilamellar vesicles. This phase and the microstructure transition were attributed to neutralization of sodium laureate to lauric acid by the formation of protons from the reaction of borax with glycerol. The variation of the charge density on the bilayer assemblies and the formation of LA were confirmed by fluorescence quenching and ATR-IR experiments. Our results demonstrate that a small amount of glycerol can be used to tailor the phases and microstructures in surfactant systems containing pH-sensitive components.