Smart droplet bouncing on dielectric surfaces under uniform electric fields

Abstract

The electric field is considered an effective stimulus to control droplet bounce or adhesion on demand on solid surfaces, which is important for various applications, including water harvesting and oil/water separation. However, it remains challenging to switch droplet bouncing/adhering on electrode surfaces smartly. Herein, we present a smart control method for droplet bouncing on dielectric surfaces by coupling charge transfer with contact electrification and a uniform electric field. Subject to electric fields, water droplets carrying the like charges in the insulating silicone oil present electric field-direction-dependent impact behaviors, bifurcating into bouncing and adhesion on hydrophobic and hydrophilic surfaces. Furthermore, oppositely charged water droplets with contact electrification led to contrary bouncing behaviors on hydrophobic and hydrophilic surfaces. The transfer charges and electric forces in the experiments are especially quantitively analyzed. By constructing dielectric pairs with hydrophobic and hydrophilic surfaces, reciprocating bouncing or selective adhesion can be modulated via switching electric field directions. This route of separately charging droplets and building electric fields facilitates droplet manipulation techniques and applications.