In situ vesicle formation by a kinetic reaction in aqueous mixtures of single-tailed catanionic surfactants

Is the vesicle phase the spontaneous formation and the thermodynamically stable state? We answer the question by developing extremely dilute cationic and anionic (catanionic) aqueous mixtures of single-tailed surfactants in situ by designing a chemical reaction without shear forces. It is demonstrated that vesicles do spontaneously form in extremely dilute catanionic surfactant systems if one of the components is produced by a chemical reaction and not by mixing of the components which avoids the influence of shear-stress forces as previously described. The results in extremely dilute solutions are compared to those of our previous results in concentrated solutions, which clearly demonstrate that the final state (vesicle phase) at lower concentration is history independent at equilibrium. It is concluded that catanionic surfactant vesicle formation is produced spontaneously in extremely dilute solutions (water-rich), and the resultant vesicle phase is a thermodynamically stable state. In concentrated solutions, however, vesicle formation is not produced spontaneously, which means the shearing forces might be responsible for the formation of vesicles as a result of the external input of energy.