Salvinia-Effect-Inspired Magneto-Responsive Superhydrophobic Surfaces with Cluster-Distributed Microcilia Array.

Inspired by the "Salvinia effect", a novel method for fabricating a magneto-responsive superhydrophobic surface coated with a cluster-distributed cilia array (CC-MRSS) was reported. This surface features a magnetically self-assembled nonuniform microcilia array and demonstrates exceptional microdroplet hydrophobicity, magnetic-responsive wettability, and corrosion resistance. The fabrication process involved mixing polydimethylsiloxane (PDMS) and carbonyl iron powders (CIPs), followed by dividing the mixture into two parts. The first part was poured into a 3D-printed female mold to form an elastic substrate with a hemispherical array. The second part was sprayed onto the substrate by using the air spray method. When an external magnetic field was applied during curing, a dense microcilia array self-assembled on the hemispheres of the substrate. As a result, the CC-MRSS, with a two-level composite microstructure, was successfully prepared. Contact angle tests showed a static contact angle of 157.0° for an 8 μL water droplet. Multiple samples were tested for controllable hydrophobicity by varying the spraying volume and CIP weight fraction. The relationship between wettability and the external magnetic field was analyzed, and a magneto-elastic coupling theory was developed to explain the contact angle variation. An optimal parameter scheme was proposed to achieve the maximum magneto-responsive contact angle range. The optimized CC-MRSS can switch between a low-hydrophobic state (118.2°) and a superhydrophobic state (151.5°) upon magnetic field switching, with high repeatability over ten cycles. Notably, the Salvinia-inspired CC-MRSS maintains an air film underwater, just like the Salvinia leaf, reducing surface-solution contact and offering superior corrosion resistance over other magnetic ciliary array surface materials.