Programmable surface-charge-modulated wettability for controllable droplet manipulation

Abstract

Droplet manipulation on open surfaces plays a key role in numerous applications. The enhancement in controllability, flexibility, and simplicity of droplet manipulation is sustainably demanded and developed. Herein, we create a unique droplet manipulation method by modulating wettability based on surface charges. With contactless charge deposition on tilting dielectric surfaces with the corona discharge generated by needle-plate electrodes, droplet sliding can be actuated in real time. Droplets show wettability enhancement after eliminating charge deposition, in which contact angle decreases reach up to ∼20°. The presented surface-charge-modulated wettability results in fast-speed (∼14 mm/s) and high-volume-range (10–80 μL) droplet manipulation. Experiments and theoretical analysis reveal the underlying mechanism of droplet actuation is surface charge gradients, which induce asymmetric electrostatic forces. Controlling charge distributions on dielectric surfaces with plate-electrode patterns, programmable, and reconfigurable droplet sliding along complex pathways can be achieved. Moreover, a droplet sliding value for controlling stepwise chemical reactions is demonstrated by moving plate electrodes.