Polyelectrolyte solutions in Taylor-Couette flows

Taylor-Couette (TC) flow is ideal for studying the flow behavior of complex solutions due to the wide variety of available hydrodynamic flow states. For non-Newtonian solutions, the presence of polymers in solution changes the solution rheology, which in turn modifies accessible flow states. While significant prior work exists on the effects of elasticity and shear thinning of polymer solutions on TC flow, the effects of changes in polymer chain conformation on these properties and the resultant changes in the TC flow states have not been extensively studied. Here, we have explored the effects of changing polymer chain conformation of polyelectrolyte solutions on laminar and turbulent TC flow by using a quasi-static ramp protocol to vary the inner cylinder rotation rates. The ionic strength of the cationic polyacrylamide (CPAM) solution was varied to modify the equilibrium polymer equilibrium conformation and solution rheological properties. In general, as the increasing solution ionic strength increases polymer chain flexibility and decreases elasticity and degree of shear thinning, there is a shift toward more Newtonian-like flow behavior. Additionally, the effects of co- and counter-rotation of the cylinders on the stability of flow states were observed as a function of solution ionic strength, and phase diagrams of the resulting flow states were mapped as a function of the inner and outer cylinder Reynolds numbers. It was found that co-rotation of the cylinders stabilizes some of the polymer-influenced flow states, while counter-rotation destabilizes flow states.