Eco-friendly Immersion-Coating Strategy for Scalable and Durable Superhydrophobic Aluminum Surfaces

Superhydrophobic (SHPB) surfaces have strong potential to mitigate corrosion, fouling, and icing, yet conventional fabrication methods rely on fluorinated modifiers, toxic reagents, or multistep protocols that limit scalability and conformal coverage on complex geometries. Here, we report an eco-friendly, scalable, and fluorine-free immersion-coating strategy for developing SHPB aluminum (SHPB-Al) surfaces using an ionic liquid (IL, 1-ethyl-3-methylimidazolium chloride) and lauric acid (LA) as nontoxic precursors. The central novelty lies in generating the requisite hierarchical roughness via an ionic liquid adsorption-driven surface modification mechanism, rather than through conventional material-removal or etching processes, thereby minimizing substrate damage and preserving structural integrity. Specifically, the two-step protocol first forms an IL-derived adsorbed substrate layer that induces hierarchical topography and hydrophilicity, followed by lauric acid functionalization to reduce surface energy and induce superhydrophobicity. Systematic optimization of the precursor concentration and dip duration identifies an optimum condition that achieves a static contact angle (SCA) of ≈165° with contact angle hysteresis (CAH) of <5°. Microscopy and surface analyses confirm the presence of hierarchical textures and robust chemical grafting. Durability tests under harsh chemical, thermal, mechanical, and environmental conditions reveal minimal performance loss (SCA > 150° and CAH < 10°), underscoring the coating's reliability. Droplet dynamics exhibit ≥15 successive rebounds, a coefficient of restitution of ≈0.9, and contact times as short as ≈10 ms, demonstrating ultralow adhesion. Building on these insights, we introduce an improvised one-step IL-LA codeposition method that simplifies the fabrication route while retaining high performance (SCA of ≈160° and CAH of ≈5°) and prolonged durability under environmental exposure. Together, this fluorine-free immersion-coating framework offers durable, scalable, and nontoxic routes for producing SHPB-Als, enabling conformal coatings on complex geometries such as heat-exchanger fins and paving the way for industrial deployment in harsh service environments.