engleski

Phase Behavior in Mixture of Cationic and Anionic Surfactants

The phase equilibria of catanionic surfactant aqueous mixtures, hexadecyltrimethylammonium bromide and sodium dodecyl sulfate have been studied by combined polarizing microscopy, light scattering, conductivity, potentiometric, electrophoretic, and surface tension measurements. The phase behavior, formation of variety of microstructures and the properties of the air/solution interface strongly depended on the molar ratio and actual concentration of surfactants. Lamellar catanionic surfactant salt was formed from equimolar mixtures of the reactants. Stable polydispersed vesicles coexisted with crystalline catanionic salt and transformed to the mixed micelles as mixtures shifted from the equimolar range. The amount of catanionic salt was reduced and the amount of vesicles increased as the surfactants molar ratio increase. The formation and stability of different phases are discussed in terms of surfactant molecular packing constraints and electrostatic effects.

adsorption; association; catanionic surfactants

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