Spontaneous formation of zwitterionic vesicles: chemical structure - vesicle formation relationships

New double-chain zwitterionic surfactants were shown to undergo spontaneous dispersion as vesicles in water by means of simple dilution of the lamellar phase. The molecular parameters of relevance were investigated in a systematic study of the structure of the lamellar phase and of the ability of spontaneous formation of vesicles in a series of homologous zwitterionic surfactants. Thus, the double-chain zwitterionic surfactants which occupies a small interfacial area per molecule in spite of the large size of their hydrophilic headgroup can form spontaneous vesicles. In this case, the bending modulus (k) over bar of the surfactant film is strongly negative and the short-range repulsive interactions between hydrophilic groups protruding from the surfactant films into water allow a large swelling of the lamellar phase, and are the origin of the colloidal stability of the vesicles dispersion.