2005 Volume 54 Issue 3 Pages 125-134
The phase behavior of mixed solutions of (11-ferrocenyl)undecyltrimethyl-ammonium bromide (FTMA+), a redox-active cationic surfactant, and sodium dodecylbenzenesulfonate (SDBS), an anionic surfactant, was investigated in detail, and the mechanisms of spontaneous vesicle formation and the control of reversible formation of vesicles through the redox reaction of FTMA+ in the mixed system were also examined. Differential interference optical microscopic observations, particle size measurements, and trapping efficiency measurements revealed that various types of aggregates including mixed micelles, vesicles, and liquid crystals are formed in the system depending on the mixing ratio of FTMA+ and SDBS. Ultracentrifugal measurements showed that the composition of bimolecular membranes composed of FTMA+ and SDBS differs from the initial surfactant mixing ratio and changes depending on the initial mixing ratio. Surface tension measurements indicated an important contribution of the formation of a pseudo-double chain-type complex through the electrostatic interaction between FTMA+ and SDBS to spontaneous vesicle formation. In addition, the existence of a benzyl group in the anionic surfactant was suggested to be important for the pseudo-double chain-type surfactant to take the orientation favorable to vesicle formation.