Facile Strategy to Generate Charged Droplets with Desired Polarities

Water droplets are usually charged positively via either electrospray or contact electrification at the solid/liquid interface. Herein, we describe a facile twostep strategy to generate charged droplets with desired polarities. In particular, negatively charged droplets can be generated via electrostatic induction using a precharged superamphiphobic substrate as an electret. The interplay of repulsive and attractive interactions between like- and unlike-charged droplets or electret leads to rapid droplet transport and self-assembly of specific highly ordered arrays.