CO2-induced micelle to vesicle transition in zwitterionic–anionic surfactant systems

Abstract

Study of micelle to vesicle transition (MVT) is of great importance from both theoretical and practical points of view. In this work, we studied the effect of compressed CO₂ on the aggregation behavior of zwitterionic–anionic (DSB (dodecyl sulfonatebetaine)–AOT(sodium bis(2-ethylhexyl) sulfosuccinate)) mixed surfactants in aqueous solution by means of direct observation, turbidity, steady-state fluorescence, fluorescence quantum yield, and entrapment quantity of vesicles. Interestingly, all the methods show that compressed CO₂ can induce MVT in this zwitterionic–anionic surfactant system. The CO₂-induced MVT is reversible and the degree of MVT can be easily tuned by controlling the operation pressure. Further studies show that the pH decrease and dissolution of gas molecules in the surfactant film co-contribute to the MVT, and a possible mechanism for the CO₂-induced MVT was proposed based on the experimental results.