SPONTANEOUS VESICLE FORMATION FROM AQUEOUS-SOLUTIONS OF DIDODECYLDIMETHYLAMMONIUM BROMIDE AND SODIUM DODECYL-SULFATE MIXTURES

Spontaneous vesicle formation in the aqueous mixture of didodecyldimet hylammonium bromide (DDAB) and sodium dodecyl sulfate (SDS) has been i nvestigated with differential interference microscopy, transmission el ectron microscopy, glucose trapping experiments, zeta potential measur ements, and surface tension measurements. The micrographs of the DDAB- SDS mixtures confirm the spontaneous formation of polydispersed vesicl es including ''giant vesicle'' with a diameter less 40 mu m. The captu red volume of the DDAB-SDS mixtures is 2.2 L/mol at the SDS mole fract ion (X(SDS)) of 0.64 and decreases with increasing X(SDS). Vesicle for mation in DDAB-SDS mixtures will occur in the X(SDS) range of 0.64-0.7 5, below the total surfactant concentration of 2.2 wt %. Surface tensi on measurements for the mixtures exhibit very low values, 23 mN/m, ind icating the ion-pairing of DDAB and SDS, a pseudo-zwitterionic surfact ant. This surfactant favors the morphology of a vesicle. The mechanism of vesicle self-formation is the penetration of SDS into the DDAB mol ecules.;In addition, spontaneous vesicles are also formed in the mixtu re of DDAB and sodium decyl sulfate.