Electrochemical On-Site Switching of the Directional Liquid Transport on a Conical Fiber

Directional liquid transport (DLT), especially that proceeding on a conical fiber (DLT-CF), is an important mass-transfer process widely used both by natural organisms and in practical applications. However, on-site switching of the DLT-CF remains a challenge due to the nontunable driving force imparted by the structural gradient, which greatly limits its application. Here, unprecedently, a facile electrochemical strategy is developed for reaching the on-site switchable DLT-CF, featuring in situ control and fast response. Depending on the poised electric potential, the droplet can either move directionally or be pinned at any position for a tunable duration time, exhibiting completely different moving characteristics from the traditional DLT-CF with no control. It is proposed that the surface hysteresis resistance, closely related to both the surface hydrogen-bonding network and the droplet topology on the fiber, can be largely altered electrochemically. The tunable hysteresis resistance works synergistically with the conical-structure-induced Laplace pressure to on-site tune the forces acting on the droplet, leading to various controllable DLTs-CF, including those with tunable distance and direction, array manipulation, and assembly line processing of droplets. The strategy is applicable for versatile liquids, offering a general approach for controllable liquid transport in fibrous systems.