Aggregation Behavior of Mixed-Counterion Double-Chained Surfactants
MINNESOTA UNIV MINNEAPOLIS
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The aggregation behavior of dilute solutions of the ditetradecyldimethylammonium surfactant cation with mixtures of bromide and acetate counterions was studied using video enhanced microscopy, cryo- transmission electron microscopy, and time resolved fluorescence quenching. Large liposomal aggregates of the bromide surfactant are gradually transformed into micellar aggregates by the addition of the acetate surfactant. Stable, equilibrium, unilamellar vesicles predominate at intermediate concentrations 40-60 Br-, while small, spherical micelles coexist with, and gradually replace, vesicles as the bromide content is further reduced. Similar behavior is seen with long chain-short chain phospholipid mixtures. These results are analyzed in terms of free energy minimization and bilayer asymmetry arguments.