Active micro-mixers utilizing a gradient zeta potential induced by inclined buried shielding electrodes

This study presents a new active micro-mixer which enhances the mixing efficiency by means of a gradient distribution of the surface zeta potential generated by applying a control voltage to an arrangement of inclined buried shielding electrodes. A theoretical model is developed to predict the distribution of the zeta potential and the thickness of the transition layer. The validity of this model is confirmed experimentally. Numerical simulations are performed to characterize the fluid flow patterns and to optimize the design of the micro-mixer. It is shown that optimizing the arrangement of the inclined shielding electrodes leads to a significant enhancement in the mixing performance of the active micro-mixer. The numerical results indicate that a localized flow circulation is generated when the control voltage is applied to the inclined shielding electrodes. The shape of this circulation is dependent on the distribution of the gradient zeta potential, which is determined in turn by the arrangement of the electrodes. The effect of the number of electrode pairs and the layout of the shielding electrodes on the mixing performance of the micro-mixer is explored both numerically and experimentally. It is revealed that the inclined electrode layouts with five electrode pairs provide the highest mixing efficiency of almost 93%. The active micro-mixer developed in this study represents a crucial advancement in microfluidic systems.