Time dependent physicochemical changes of SDS-CTAB interacted self assembled vesicles: Ostwald ripening effect

Abstract

It is found that oppositely charged surfactants SDS (sodium dodecyl sulfate) and CTAB (cetyltrimethylammonium bromide) at low concentrations (< critical micelle concentration or CMC) interact, and form self-assemblies (vesicles) in aqueous medium. Physicochemical characterization of the assemblies has been studied and reported. It has been found that the characteristic properties of these assemblies change with time. Investigations on the time dependent changes of such vesicles have been monitored over a period of three months. The properties studied were, turbidity, surface tension, conductance, size and shape, ζ-potential, fluorescence anisotropy and quenching of photosensitive dyes in them, thermodynamics of formation as well as toxicity. The surfactants (well below their CMCs) were mixed in different proportions making the final concentration of all at 0.6 mM. They were kept at temperature 303 K, and examined at different times (on the day of mixing, and subsequently after 10, 30, 60, and 90 days). It is known that by the phenomenon of Ostwald Ripening (OR) process, morphological changes in colloidal solution takes place; larger particles grow in size with time at the expense of smaller particles.We studied the OR effect on the physicochemical properties of the growing SDS-CTAB interacted vesicles in aqueous medium. Results and their documentations are herein presented. Such an elaborate study of vesicles with reference to OR process as per our knowledge was not done in the past.