Strong Flows of Viscoelastic Wormlike Micelle Solutions

The unique rheological properties of viscoelastic wormlike micelle solutions have led to their broad use as rheological modifiers in consumer products such as paints, detergents, pharmaceuticals, lubricants and emulsifiers. In addition, micelle solutions have also become increasingly important in a wide range of industrial and commercial applications including agrochemical spraying, inkjet printing, turbulent drag reduction and enhanced oil recovery. Until recently, our knowledge of the rheology and flow behavior of these fluids was limited to linear viscoelasticity measurements where wormlike micelle solutions have been shown to behave as ideal Maxwell fluids, and steady shear rheology measurements where wormlike micelles often demonstrate shear banding. In this review, we survey recent experimental and theoretical developments for nonlinear rheology of viscoelastic wormlike micelle solutions and the response of these complex fluids to strong flows. Specific emphasis will be placed on extensional rheology measurements and complex flows having strong extensional components. In many of these flows, viscoelastic wormlike micelle solutions behave in a manner very similar to polymer solutions. Wormlike micelle solutions demonstrate strain hardening of their extensional viscosity which can result in an increased resistance to complex flows such as the flow past a sphere or the flow through porous media. Additionally, the large extensional viscosity of these fluids has led to significant drag reduction in turbulent flows. However, wormlike micelles are self-assembled and as such are quite different than polymer solutions. Under large elastic stresses, wormlike micelles can break apart. This failure and the resulting morphological changes have been linked to a number of newly discovered elastic instabilities not present in polymer solutions. As this review will show, strong flows of wormlike micelle solutions hold a wealth of interesting flow phenomena much of which is yet to be explored.