Onion-Like Structure of Viscoelastic Surfactant Solution Flow Induced by 4-Blade Paddle Impeller in a Vessel

Abstract

Aqueous solutions of some kinds of surfactants and counterions are known as viscoelastic fluids. The rheological properties and fluidity of the solutions are significantly affected by the surfactant and counterion concentrations. Thus, the solution is a potential solvent for industrial applications because a drastic change in the fluidity can be realized only through the addition of counterions. In this study, we focused on the characteristics of the fluid flow of viscoelastic surfactant solutions in a mixing vessel. It was found that in the vicinity of the impeller the fluid was actively mixed and contained a large number of laminated fluid lumps, forming onion-like structure. When the elastic force becomes comparable to the viscous force, the micellar network of the surfactant was deformed. Additionally, if the elastic force was not much smaller than the inertia force, the impeller region was covered by a network-deformed fluid and an onion-like structure was then formed. Moreover, a stable onion-like structure was obtained when the impeller rotated as slowly as possible or when the elastic force of the solution was more significant than the viscous one.