Reversible phase transition between salt-free catanionic vesicles and high-salinity catanionic vesicles

Abstract

Reversible phase transition between salt-free cationic and anionic (catanionic) tetradecyltrimethylammonium laurate (TTAL) birefringent L_α-phase solution with uni- and multilamellar vesicles and high-salinity catanionic vesicles was studied. With increasing concentration of NaBr, the salt-free catanionic birefringent Lα-phase formed by cationic tetradecyltrimethylammonium hydroxide (TTAOH) mixing with lauric acid in equimolar ammounts in aqueous solution was transferred into a two-phase precipitate–L₁-phase, and finally a birefringent L_α-phase again at much higher salt concentration. The uni- and multilamellar vesicles of birefringent L_α-phases without salt and with much higher salts were determined by freeze-fracture transmission electron microscopy (FF-TEM) images. The precipitates being the top phase at the two-phase region were also determined by means of FF-TEM images, which consist of densely packed multilamellar vesicles. The phase transition from salt-free catanionic birefringent L_α-phase to the one with much higher salinity is reversible, which could be achieved by removing the salts through dialysis. Salt-free catanionic birefringent L_α-phase with uni- and multilamellar vesicles, via the densely packed multilamellar vesicles of precipitates that have a lower density than water to another birefringent L_α-phase at high-salinity, and also the reversible process should improve our understanding of self-assembled structures of surfactants in completely different solvents such as in pure water and ionic liquid media, which may make a significant impact on surfactant sciences.