The DODAB–AOT–water system: vesicle formation and interactions with salts or synthetic polyelectrolytes

Soft Matter Pub Date: 2013-07-31 DOI: 10.1039/C3SM51624E

Abstract

The phase behavior of the dioctyldimethylammonium bromide (DODAB)–sodium bis(2-ethylhexyl)sulfosuccinate (AOT)–water system was determined. Studies dealt with dilute concentration regimes, at an overall surfactant concentration lower than 30.0 mmol kg?1, and in the cationic rich side. The system was investigated by combining visual inspection with optical microscopy, fluorescence microscopy, dynamic light scattering, small-angle X-ray scattering, and electrophoretic mobility. At high [DODAB]/[AOT] mole ratios, stable and unilamellar catanionic vesicles are observed in a narrow region of the phase diagram. Vesicles are characterized by nearly constant hydrodynamic diameters, in the 300–400 nm size range, and positive ζ-potentials (about 40–50 mV). A further increase of AOT content induces the onset of a biphasic region, where vesicles are in equilibrium with a lamellar phase. In the above concentration regimes, addition of sodium bromide destabilizes vesicles and favors the formation of a lamellar phase. Under the same conditions, conversely, a synthetic polyelectrolyte, sodium polyacrylate, does not alter the phase behavior. It induces the growth of particle size and decreases the ζ-potential. The complexes formed by catanionic vesicles and sodium polyacrylate aggregate and form clusters, and readily re-dissolve when more polymer is added.

Graphical abstract: The DODAB–AOT–water system: vesicle formation and interactions with salts or synthetic polyelectrolytes
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