Directional Droplet Transport and Fog Removal on Textured Surfaces Using Liquid Dielectrophoresis

This paper reports a droplet super-spreading and directional transport device using anisotropic ratchet conveyors (ARCs) and liquid dielectrophoresis (L-DEP). The ARC is created by patterning micro-sized hydrophilic curved rungs on a hydrophobic background. Micropatterning processes on the hydrophobic thin film have been successfully implemented by adopting a Parylene C stencil mask. The application of ARCs to transport the droplet using orthogonal vibrations to create self-cleaning surfaces was reported at the Hilton Head Workshop in 2018. The method presented in this paper utilizes interdigitated electrodes (IDE) to exert an L-DEP force on the droplet. By modulating the L-DEP force with an electromagnetic relay, the droplet can be directionally transported on the ARC-patterned surface independently of the droplet self-resonance frequency. The system works with a broad range of droplet volumes between $2~\mu \text{L}$ and $20~\mu \text{L}$ . The droplet can be transported with the presence of a moisture layer on the surface, which is superior to systems that move the droplet by relying on the solid-liquid interfacial tension difference like, e,g., in an electrowetting-on-dielectric (EWOD) system, since the moisture could block the solid-liquid interface and degrade the system ability to transport the droplet. This design also enables droplet manipulation in an open space configuration without a top cover plate, leading to a broad range of applications including self-cleaning surfaces and fog removal. [2020-0077]