title: Spontaneous vesicle formation of mixtures of double-chain cationic surfactants with a different counterion.
abstract: Aggregate formation of a didodecyldimethylammonium bromide (DDAB) and didodecyldimethylammonium chloride (DDAC) mixture in aqueous solution was investigated. The concentration vs composition diagram of aggregate formation was constructed by analyzing the surface tension, turbidity, and electrical conductivity data. The cryogenic transmission electron microscopy was applied to several representative points in the diagram and provided information of the morphology of aggregates. The sequence of monomer (m) - m + small aggregate (A) - m + A + vesicle (V) - m + V was concluded with increasing total concentration of surfactants at all mixing ratios. The compositions of counterions in A and V were estimated on the basis of thermodynamic consideration and examined from the viewpoint of asymmetry of constituents and uneven distribution between outer and inner monolayers of a vesicle bilayer. Vesicle surfaces were suggested to abound in chloride ions compared to bulk solution, which is opposite to spherical micelle surfaces.
authors.affiliation: Department of Chemistry, Faculty of Sciences, Kyushu University, Fukuoka, Japan. aratono@chem.kyushu-univ.jp
authors.forename: Makoto
authors.initials: M
authors.lastname: Aratono
authors.forename: Azusa
authors.initials: A
authors.lastname: Mori
authors.forename: Ikuyo
authors.initials: I
authors.lastname: Koga
authors.forename: Makiko
authors.initials: M
authors.lastname: Shigehisa
authors.forename: Nami
authors.initials: N
authors.lastname: Onimaru
authors.forename: Koji
authors.initials: K
authors.lastname: Tsuchiya
authors.forename: Takanori
authors.initials: T
authors.lastname: Takiue
authors.forename: Hiroki
authors.initials: H
authors.lastname: Matsubara