title: Effect of equimolar salt to decyltrimethylammonium decyl sulfate on vesicle formation and surface adsorption.
abstract: The aqueous solution of mixture of sodium decyl sulfate (SDeS) and decyltrimethylammonium bromide (DeTAB) has been found to form equilibrium multilamellar vesicles (MLV) spontaneously. We measured the surface tension of the aqueous solution of 1:1 mixture of SDeS and DeTAB as a function of temperature T at various molalities m under atmospheric pressure. The surface density, the entropy of adsorption and the entropy of vesicle formation are evaluated and compared with those of the decyltrimethylammonium decyl sulfate (DeTADeS) aqueous solution system to investigate the role of small counterions in the mechanism of equilibrium vesicle formation. The saturated surface density Gamma (H,C ) vs T curve of the SDeS/DeTAB system sits below that of the DeTADeS system. Therefore, sodium and bromide ions are negatively adsorbed and nevertheless, they neutralize the electric charge of the decyl sulfate ion DeS(-) and the decyltrimethylammonium ion DeTA(+) to some extent to weaken the electrostatic attraction between the polar head groups in the adsorbed film. The net surfactant concentration required for vesicle formation was larger in the SDeS/DeTAB system. Hence, the electrostatic attraction between the polar head groups of the surfactant ions which is one of the major driving forces for vesicle formation is weakened by the presence of the counterions Na(+) and Br(-). Small but distinct changes in the surface density and the entropies of MLV formation of the SDeS/DeTAB system from those of the DeTADeS system were also found.
authors.affiliation: Department of Biological Science and Technology, Faculty of Engineering, University of Tokushima, Minamijosanjima, Tokushima 770-8506, Japan. villeneuve@chem.saitama-u.ac.jp
authors.forename: Masumi
authors.initials: M
authors.lastname: Villeneuve
authors.forename: Shoji
authors.initials: S
authors.lastname: Kaneshina
authors.forename: Makoto
authors.initials: M
authors.lastname: Aratono
mesh_terms: D000327:Adsorption; D000644:Quaternary Ammonium Compounds / Q000737:chemistry* / Q000493:pharmacokinetics*; D013501:Surface-Active Agents / Q000737:chemistry* / Q000493:pharmacokinetics*; D013696:Temperature
chemical_list: D000644:Quaternary Ammonium Compounds; D013501:Surface-Active Agents; C013912:decyltrimethylammonium