Single-process fabrication of superomniphobic surfaces utilizing freestanding plasma-deposited fluoropolymer structures

Omniphobic surfaces are capable of repelling a wide range of liquids, including low-surface-tension oils. This contrasts with superhydrophobic surfaces, which only repel water and other liquids with high surface tension. One problem with omniphobic surfaces is that the fabrication processes tend to be more complicated and include more steps than those of superhydrophobic surfaces. The reason is the re-entrant pillar geometries that are required for omniphobicity. In this study, we present two streamlined, proof-of-concept fabrication processes that create doubly re-entrant pillar structures in a single, uninterrupted, multi-step etching process executed in one plasma reactor and requiring only one lithography step. The key innovation is a self-aligning process that uses plasma-deposited fluoropolymer (C₄F₈) as a freestanding structural component of the overhang, rather than merely a hydrophobic coating, enabling complete fabrication without tool changes. We show that the fabricated surfaces reliably repel low-surface-tension liquids, including 2-propanol and ethanol, as demonstrated by high dynamic contact angles, low sliding angles, and droplet rebound upon impact. In the best-performing sample, the advancing contact angle for 2-propanol was measured at 164°, with a receding contact angle of 135°, and droplets rebounded from the surface.