Microfluidic mixing enhancement using electrokinetic instability under electric field perturbations in a double T-shaped microchannel

Abstract

The electrokinetic instability (EKI) phenomenon occurs when microfluidic flows with an electrical conductivity gradient are driven by a high-intensity external electrical field. Although EKI limits the robust performance of complex electrokinetic bioanalytical systems, it can be actively exploited to achieve the rapid mixing of micro- and nanoliter volume solutions in microscale devices. This paper investigates the EKI phenomenon in a double T-shaped microchannel, in which two aqueous electrolyte solutions with a 3.5:1 conductivity ratio are driven electrokinetically into the mixing channel via the application of a DC electrical field. A stratified flow condition is formed when the intensity of the applied DC electrical field is below a certain threshold value. However, as the intensity is increased, a series of flow circulations forms at the interfaces of neighboring solutions flows, and then propagates in the downstream direction when the intensity of the electrical field is increased beyond a certain critical threshold value. Electrical field intensity perturbations aligned in the direction of the conductivity gradient are then added to the DC electrical field at the upper inlet of the double T-shaped microchannel near the main mixing channel. It is found that these perturbations can stir the microfluidic instability and the induced flow instability conditions can enhance the mixing efficiency.