Rheology mediates transition of vortex evolution patterns in microcavity flow of polymer solutions

Abstract

Vortex instability in cavity flow is a fundamental component of microfluidic applications such as flow mixing, nanoparticle synthesis, and cell/particle manipulation. In contrast to Newtonian fluids, non-Newtonian fluids exhibit significantly different flow behaviors due to their non-linear flow dynamics. This study experimentally investigates the flow dynamics of polymer solutions with distinct rheological properties through a microcavity and quantifies the influence of the rheological degree on the evolution dynamics of vortices. We find three typical vortex evolution patterns in the cavity flow of polymer solutions and show that the rheological degree mediates the transitions among these patterns. The vortex evolution in the cavity flow of all polymer solutions tested in this study shifts from a basic increasing logistic function to one of three typical patterns as the polymer concentration increases. It is clarified that the pattern transition is related to the elasticity number and shear-thinning index of the fluids, and the phase difference between identical patterns is due to differences in the viscosity and elasticity of the fluids. These results extend our understanding of the vortex dynamics of complex fluids in cavity flow and provide theoretical guidance for enhancing the working efficiency of cavity-structured microfluidic applications using polymer solutions. The results of this study may also inspire developments in the flow regulation of drug delivery in blood through the vascular system.