Microstructures and rheological dynamics of viscoelastic solutions in a catanionic surfactant system

Microstructural transitions and rheological properties of viscoelastic solutions formed in a catanionic surfactant system were studied using a combination of rheology and dynamic light scattering. Viscoelastic solutions formed in a catanionic surfactant system of dodecyltriethylammonium bromide (DTEAB)/sodium dodecylsulfate (SDS) at the molar ratio of 27/73 were systematically studied using a combination of rheology and dynamic light scattering (DLS). Wormlike micelles began to form above the total surfactant concentration ( C total) of 120 mM by the growth of small cylindrical micelles. Subsequently the system was found to exhibit linear viscoelasticity with characteristic of a Maxwell fluid in the intermediate concentration range of 170–210 mM, which arose from a 3D entangled network of wormlike micelles. At higher surfactant concentrations, a transition from linear micelles to branched structures probably took place. Finally and significantly, the effect of the surfactant headgroup on the rheological property of catanionic surfactant mixtures was discussed.