Rheology and Dynamic Adsorption of Polymer-Surfactant Complexes

The rheological properties of polymer-surfactant mixtures play a significant role in applications ranging from enhanced oil recovery, pharmaceutical and biological fluids, cosmetics, food, and coating. Addition of an ionic surfactant to an aqueous solution of neutral polymer like polyethylene oxide is known to result in a shear rheological response with non-monotonic concentration dependent variation, attributed to association complexes formed by hydrophobic interactions between surfactant monomers and polymers chains, as well as charge effects. Furthermore, the formation of association complexes changes both dynamic and equilibrium surface tension. However, due to a lack of suitable techniques, extensional rheology response of polymer-surfactant mixtures has not been characterized in adequate detail, even though most processing flows, especially those involving drop formation or liquid transfer are influenced by extensional rheology and pinch-off dynamics. In this study, we examine how pinch-off dynamics and the extensional rheological response of polymer solutions are modified by the addition of ionic surfactants. We utilize dripping-onto-substrate rheometry protocols and show that shear and extensional rheology response display contrasting concentration-dependent variation.