Adsorption, association and precipitation in hexadecyltrimethylammonium bromide/sodium dodecyl sulfate mixtures

• Published in: Colloid and polymer science Vol. 277; no. 2-3; pp. 153 - 163
• Main Authors: TOMASIC, V, STEFANIC, I, FILIPOVIC-VINCEKOVIC, N
• Format: Journal Article
• Language: English
• Published: Berlin Springer 03.03.1999; Springer Nature B.V
• Subjects: Adsorption; Chemistry; Crystal structure; Electrostatics; Exact sciences and technology; Gas-liquid interface and liquid-liquid interface; General and physical chemistry; Precipitation; Sodium; Sulfates; Surface chemistry; Surface physical chemistry; Surface-active agents: properties; Surfactants; Vesicles; Quaternary ammonium compound; Gas liquid interface; Anionic surfactant; Monolayer; Precipitation; Association; Adsorption; Electrostatic interaction; Cationic surfactant; Sodium compound; Experimental study; Lauryl sulfate
• ISSN: 0303-402X; 1435-1536
• DOI: 10.1007/s003960050380

The phase equilibria of surfactant aqueous mixtures, hexadecyltrimethylammonium bromide and sodium dodecyl sulfate, have been studied by polarizing microscopy, quasielastic light scattering, conductivity, potentiometric, electrophoretic, and surface tension measurements. Adsorption at the air/solution interface, association and precipitation in bulk solution strongly depended on the molar ratio and the concentration of surfactants. Catanionic vesicles coexisted with crystalline catanionic salts in a broad concentration range. The relative proportions of crystallites and vesicles varied according to the concentration and the molar ratio of the surfactants. The solid crystalline phase was progressively converted to catanionic vesicles with increasing surfactant molar ratio. At the highest excess of one of the surfactants transition from catanionic vesicles to mixed micelles occurred. The formation and stability of different phases are discussed in terms of surfactant molecular packing constraints and electrostatic interactions in the headgroup region. Surfactant tail-length asymmetry and the change of electrostatic interactions in the headgroup region from attractive to repulsive are governing factors for the transition from planar to curved bilayers.[PUBLICATION ABSTRACT]