Triboelectric “Electrostatic Tweezers” for Manipulating Droplets on Lubricated Slippery Surfaces Prepared by Femtosecond Laser Processing

“Electrostatic tweezer” is a promising tool for droplet manipulation, but it faces many limitations in manipulating droplet on superhydrophobic surfaces. Here, we achieve noncontact and multifunctional droplet manipulation on Nepenthes-inspired lubricated slippery surfaces based on triboelectric electrostatic tweezers (TETs). The TET manipulation of droplets on a slippery surface shows many advantages over the electrostatic droplet manipulation on a superhydrophobic surface. The electrostatic field induces the redistribution of the charges inside the neutral droplet, which makes the triboelectric charged rod drive the droplet to move forward under the electrostatic force. Positively or negatively charged droplets can also be moved by TET based on electrostatic attraction and repulsion. TET enables manipulate droplets under diverse conditions, such as anti-gravity climb, the motion of suspended droplets, corrosive liquids, low-surface-tension liquids (e.g., ethanol with a surface tension of 22.3 mN/m), different droplet volumes (from 100 nL to 0.5 mL), passing through narrow slits, sliding over damaged areas, on various solid substrates, and even droplets in an enclosed system. Various droplet-related applications, such as motion guidance, motion switching, droplet-based microreactions, surface cleaning, surface defogging, liquid sorting, and cell labeling can be easily achieved with TET.