Heterogeneous Surface Charge Enhanced Micro-Mixer for Electrokinetic Flows

Enhancing species mixing in microfluidic applications is key to reducing analysis time and increasing device portability. Mixing in electroosmotic flows is usually diffusion-dominated requiring extended channel lengths and retention times. Recent numerical studies have indicated that the introduction of electrically charged surface heterogeneities may augment mixing efficiencies by creating localized regions of flow circulation. In this study, we experimentally visualize the effects of surface charge patterning and develop an optimized electrokinetic micromixer applicable to the low Reynolds number regime. Using the optimized micro-mixer, mixing efficiencies were improved between 22% and 68% for applied potentials ranging from 70–555 V/cm when compared with the homogeneous case. For 95% mixture, this equates to a potential decrease in required mixing channel length of up to 88% for flows with Pe´clet numbers between 190 and 1500.