.----------------------------------,

Despite the fact that many papers have been published on the spontaneous vesicle formation of catanionic surfactants, there are only several reports from the standpoints of the surface tension's and the solution surface's being equilibrium with the vesicle particles [28,37-40]. Here we review

first our recent work on a simple model of the molality versus mole fraction diagram of aggregate formation and the spontaneous vesicle formation of the decyltrimethylammonium bromide (DeT AB) + sodium decyl sulfate (SDeS) mixture [28] and then the work on the dodecylammonium chloride (DDACl) + sodium dodecyl sulfate (SDS) mixture ofFilipovire-Vincekovire et al. [38]. Furthermore, as described above in detail, double long-chain cationic surfactants, e.g., didodecyldimethylammonium bromide (DDAB), are known to spontaneously form vesicles by themselves. Therefore, it is expected that the mixture of a usual micelle-forming surfactant with (R1 R2)+x-may also spontaneously form vesicles within a certain mixing ratio. There are several papers from this point of view [22,24,25,41]. Next the surface tension study of Viseu et al. [25] will be introduced.