Effective Manipulation of Water Droplets on Open Superhydrophobic Glass Surfaces by Using a Triboelectrically Charged Polytetrafluoroethylene Rod on the Back Side of These Surfaces

Effectively controlling the motion of water droplets on open surfaces is crucial in digital microfluidics. Therefore, this study develops a triboelectric method that involves using a polytetrafluoroethylene (PTFE) rod on the back side of a substrate for controlling the movement of water droplets on the opposite side of the substrate. Glass substrates with silica nanowires are prepared, and surface treatment is then performed to ensure superhydrophobicity. Results indicate that the triboelectric static electricity generated on a PTFE rod is sufficient for driving water droplets on the prepared substrates. The droplets can be controlled to move along specific trajectories over an extended period without any water being lost; the droplets’ speed and acceleration can exceed 100 mm s⁻¹ and 10 000 mm s⁻², respectively. Droplets with various volumes can be controlled using the aforementioned method, which enables the method to be effective even when droplets mix to produce larger droplets. Moreover, water droplets can be collected over long distances by leveraging electrostatic forces, and the proposed method is effective even in hexane solvents. Finally, Raman signal detection can be enhanced for trace molecules by mixing water droplets containing silver nanoparticles and rhodamine 6G molecules after rapidly oscillating them by using the proposed method.