Exploiting Stray Electric Fields in Maskless Electrochemical Machining for Spatially Programmable Superhydrophobic Tapered Microstructure Arrays.

The ability to program wettability on metal-based surfaces beyond static superhydrophobicity provides new opportunities for controlling liquid-solid interactions and designing multifunctional interfaces. However, achieving spatially programmable wettability on metal surfaces through efficient and scalable fabrication remains challenging. This study proposed a maskless electrochemical machining (ECM) strategy based on a through-hole array cathode to directly fabricate tapered microstructure arrays with tunable wettability on 304 stainless steel by intentionally utilizing stray electric fields. Three-dimensional Multiphysics simulations elucidate the stray electric fields induced nonuniform anodic dissolution mechanism responsible for tapered microstructures formation and reveal the role of cathode hole diameter in regulating tapered microstructures evolution and characteristic dimensions. By systematically varying cathode hole diameter and feed distance, a wettability design map correlating processing parameters with water contact angle was established. After fluorosilane modification, the optimized surface achieved a maximum water contact angle of 164°. Furthermore, spatially programmable wettability ranging from 148° to 162° was realized on a single surface solely by varying cathode hole diameter at a fixed feed distance of 0.8 mm. This work transforms the traditionally undesirable stray electric field in ECM into a controllable tool for programmable superhydrophobic interface fabrication and provides new insights into electric-field-driven microstructure engineering for wettability regulation.