Saturation and texture geometry effects on plastron longevity on superhydrophobic surfaces

Abstract

Superhydrophobic surfaces (SHSs), when immersed in water, sustain an underwater interfacial air layer (plastron) whose longevity governs performance. Under quiescent conditions this longevity is set by diffusive gas transfer. In this work, effects of dissolved-gas saturation and texture geometry over plastron longevity were quantified on 3D-printed micro-post arrays. Seven textures were fabricated by masked stereolithography and spray coating of nanoparticles, yielding apparent water contact angles more than 150°. Experiments were performed in quiescent deionized water at dissolved-air saturation of S = 20%, 40%, and 60%. Plastron evolution and wetting transition from the Cassie-Baxter to Wenzel states were tracked using two optical setups (top- and side-view). Across all geometries, the plastron lifetime τ increased with S. Geometry exerted a systematic influence. Increasing the inter-post gap g shortened τ, whereas increasing the post height h increased τ. Variations in the diameter d produced a comparatively weak effect over the tested range. Side-view imaging resolved stepwise depinning with transient pinning at multiple elevations along the post sidewalls. A compact response-surface model captured dependence on geometry and saturation within the measurement domain was proposed. These results provide insight and quantitative guidance for designing SHS textures that maximize plastron persistence under quiescent conditions.