Deciphering viscosity‐driven mechanisms governing chaotic flow dynamics and mixing efficiency in micromixers

Abstract Understanding how viscosity modulates chaotic dynamics in microfluidic systems has remained elusive, despite its importance for high‐viscosity mixing. This study investigates viscosity‐dependent chaos and mixing in an oscillating feedback micromixer (OFM) through experiments and simulations. Systematic Reynolds‐number correlations reveal that feedback intensity, vorticity, deformation, vortex distortion, and helicity all follow unified inertia‐dominated scaling laws, indicating a common chaotic evolution mechanism linked with viscosity. Attractor reconstruction and Lyapunov analysis demonstrate the viscosity tolerance of the chaotic state, showing only a moderate attenuation of chaotic intensity once chaos is established. Within the chaotic regime, multiscale mixing metrics (mixing efficiency and norm, micromixing time) show consistent Reynolds‐number‐dependent scaling‐law behavior, with mixing efficiency and micromixing time sharing an exponent of about 0.25. These results establish a unified viscosity‐mediated Reynolds linkage among secondary flows, chaotic advection, and multiscale mixing, clarifying that viscosity primarily shifts the transition threshold while inertially intensified chaos governs mixing performance.