Flow-switching and mixing phenomena in electroosmotic flows of viscoelastic fluids

The present study uses numerical simulations and experiments to investigate the electroosmotic flows of viscoelastic fluids through a microchannel containing a cylindrical obstacle. As the electric field strength gradually increases, the flow dynamics within this microfluidic setup becomes chaotic and fluctuating. Notably, numerical simulations reveal a flow-switching phenomenon in viscoelastic fluids when the applied electric field strength exceeds a critical value, which is absent in simple Newtonian fluids under identical conditions. Corresponding experiments confirm these observations. Additionally, this study demonstrates the successful mixing of two viscoelastic fluids using the flow-switching phenomenon within the present microfluidic setup. To gain insight into the dynamics of coherent flow structures arising from the flow-switching phenomenon and their impact on the mixing process, data-driven dynamic mode decomposition (DMD) analysis is employed. Importantly, the DMD analysis uncovers the presence of upstream elastic instability, which is not discernible through traditional velocity or concentration field plots. Overall, this study aims to advance our understanding of the electrokinetic flow behavior of viscoelastic fluids in complex systems like porous media. Furthermore, it proposes a relatively simple and fabricable microfluidic technique for efficiently mixing viscoelastic fluids.