Electrode-Free Three-Dimensional Droplet Manipulation on Open Superhydrophobic Surfaces via Triboelectric Charging

Abstract

Open-surface microfluidics provides direct access to liquids and offers unique advantages for chemical and biological processing, yet most existing platforms remain limited to individual manipulation functions or planar droplet transport. Here, we present an electrode-free programmable open-surface liquid-handling platform that integrates two-dimensional droplet transport with reliable airborne inter-substrate transfer through coordinated triboelectric electrostatic control. Localized charge printing on superhydrophobic glass creates programmable docking sites, while independently charged polytetrafluoroethylene (PTFE) controllers provide the electrostatic forces required for droplet capture, lifting, transport, and release, without embedded electrodes or continuous power supplies during operation. Integrated liquid-handling workflows were demonstrated using precipitation and colorimetric reactions, in which reacted droplets were picked up, transferred between independent substrates, and repositioned without visible liquid residue. Charge characterization, force analysis, and Maxwell stress tensor simulations show that switching of the electrostatic force balance governs transitions among mobile, captured, transported, and positioned droplet states. This work provides a general framework for programmable open-surface liquid handling through coordinated triboelectric electrostatic control.