Adsorption, association and precipitation in hexadecyltrimethylammonium bromide/sodium dodecyl sulfate mixtures |
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Authors: | V Tomašić I Štefanić N Filipović-Vinceković |
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Institution: | (1) Department of Physical Chemistry Ruďer Bošković Institute P.O. Box 1016, HR-10001 Zagreb Croatia e-mail: filipovic@rudjer.irb.hr, |
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Abstract: | 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.
Received: 9 June 1998 Accepted: 18 August 1998 |
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Keywords: | Catanionic surfactant hexadecyltrimethylammonium bromide mixed micelles mixed monolayer sodium dodecyl sulfate vesicles |
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