Highly transparent PAA-functionalized porous silica coatings with underwater superoleophobicity and oil-fouling...

Transparent underwater superoleophobic coatings hold great promise for underwater optics and marine devices, but their practical application is hindered by the inherent conflict between optical transparency, mechanical robustness, and oil-repellent durability. Here, we report a high-performance transparent underwater superoleophobic (TUS) coating designed by covalently anchoring high-molecular-weight poly(acrylic acid) chains onto a robust, porous nano-silica scaffold. The highly hygroscopic PAA chains form a stable hydration layer on the nanostructured surface, which is critical for achieving underwater oil repellency. This rational design combines mechanical stability with a stable hydration layer, enabling the coating to exhibit high transparency (92.3% in water at 550 nm), robust underwater superoleophobicity (oil contact angle: 169° ± 2°; sliding angle: 1.5° ± 0.3°), and near-zero oil adhesion (adhesion force ≈ 0.48 µN). Crucially, the TUS coating demonstrates good durability under the tested conditions, maintaining its anti-oil-fouling performance and optical clarity after prolonged exposure to high-salinity environments (20 days in 3.5 wt% NaCl), elevated temperatures (up to 70 °C), hydrodynamic shear (0.5 m s^-1 for 12 hours), and mechanical abrasion. This work provides a feasible strategy for designing multi-functional coatings for demanding applications in underwater optical and marine equipment.