Vesicular Phase Behaviour in Ionic Surfactant Systems with Organic Counter-ions

Abstract

Abstract Phase diagrams at 298.2 K were determined for aqueous systems of alkylamines and alkanoic acids in equimolecular ratio, i.e. for alkylammonium alkanoates. The bilayer structural evolution for these ionic surfactants with organic counter-ions in water was studied using transmission electron microscopy (TEM), optical microscopy, small-angle X-ray scattering (SAXS) and rheological measurements. The formed vesicles are highly viscoelastic and have a yield stress value. In the pentylammonium nonanoate-water system at higher contents, the vesicles collapse to micelles, while in the hexylammonium nonanoate-water and in the pentylammonium decanoate systems, a transition to a fully expressed lamellar phase is observed. The results are discussed in terms of electrostatic interactions and membrane flexibility.