Alternating current electrothermal actuation for microvalve function in capillary transport systems

In this article, we show a novel approach to control the flow of immiscible binary fluids through a parallel plate capillary. The top and bottom walls are asymmetrically patched with two different wettabilities. We adopt the alternating current electrothermal (ACET) mechanism to drive the fluids and the diffuse interface formalism to track the interfacial motion. Our observations reveal that interfacial motion and its dynamics can be effectively controlled by varying the chemical characteristics of the surface and tuning the electrical parameter. The wettability contrast and patch width strongly affect the acceleration-deceleration motion of the interface and interface pinning at specific locations. We delineated mechanisms for utilizing the electrothermal force effectively to control the flow speed and residence time of the interface at designated locations along the channel by altering the frequency of the electrical signal. The present study thus unveils a novel microvalving mechanism achieved via effective tuning of the interfacial electrochemistry, where active and passive control mechanisms can be utilized simultaneously to achieve control over the interfacial motion of the two-phase system.