Dynamics and flow in a viscoelastic mixed surfactant system and interactions with colloidal zinc oxide nanoparticles

Viscoelastic surfactant solutions have become the focus of extensive research in modern science, partially due to extremely unusual and fascinating rheology. Although classic systems such as CTAB and CPyCl have been extensively studied, there are very few systematic studies that address the behavior of surfactant mixtures and even fewer in which particles and micelles are combined. In this work, the bulk viscoelastic properties and the local dynamics of a system of entangled rod-like micelles and colloidal ZnO nanoparticles has been systematically investigated using rheology and light scattering methods.; A series of rheology experiments have been performed in order to quantify the viscoelastic material parameters of the mixed surfactant system as a function of NaCl concentration. The results presented here indicate that the viscoelastic parameters change dramatically as a function of salt concentration, therefore rendering the study of the non-linear flow as a function of the viscoelastic parameters of the surfactant system possible. The results have been analyzed in terms of well-known theoretical models and the non-linear flow behavior seems to be strongly dependent on the breaking and recombination events that take place in the micellar network; something that is experimentally observed here for the first time.; A stable suspension of ZnO particles within this micellar network has been created and the effect of the addition of particles to the system has also been quantified through changes in the bulk rheology (viscoelastic parameters). Lastly, the dynamics of the suspended particles have been quantified using DWS and a microrheological approach, in order to provide further insight into the interactions between the particles and the micelles. With this work, we hope to have further advanced the understanding of non-linear flow behavior of viscoelastic surfactant systems, and also to provide formulators with insightful information that will aid in the development of efficient delivery systems for colloidal particles from surfactant solutions.