Electromigration-triggered programmable droplet spreading-Yongmei Zheng

Controlled spreading of droplet on solid surface bursts out of strong applications from micro-fluidic sensors to artificial intelligence settings. Recently, to extend its application range, reversible spreading has been realized by introducing external stimulate to change the direction of wetting gradient. Here, we propose a new strategy for temporospatial control of droplet spreading (along or against the wetting gradient) by mediating current intensity (not current direction as previous reported) via the electromigration of oxygen adatom. The results indicate that, during the electromigration process, two gradients, i.e., wetting gradient and temperature gradient, are formed and the battle between these two gradients leads to the formation of an equilibrium position. No matter where droplet is dripped, it will spread toward this equilibrium position. More importantly, the equilibrium position could be easily adjusted by current intensity and predicted via our theoretical model, i.e., the spreading behaviour of droplet could be programed via current intensity. We envision this new strategy of programmable spreading of droplet could be valuable in practical applications involving fluidic transport, such as microreactor.