OSTE Superhydrophobic Synthetic Paper (SUSP) with Superior Plastron Stability by Capillary Effect

Inspired by the air transport system in submerged lotus roots, we develop a superhydrophobic synthetic paper (SUSP) based on an off-stoichiometry thiol-ene (OSTE) polymer, capable of sustaining a stable underwater plastron through spontaneous capillary-driven air replenishment. The material is fabricated by coating a lithographically patterned interlocked micropillar array (synthetic paper) with a hydrophobic spray, yielding a porous, low-cost surface with a water contact angle of 155.2° ± 1.6° and a sliding angle of 3.8° ± 0.3°. When partially exposed to air, SUSP rapidly restores a depleted plastron in sub-second timescales (e.g., 0.23 s for a 0.5 cm wide sample) and maintains full plastron coverage for over 12 h in degassed water, significantly outperforming fully submerged controls. Parametric studies reveal that plastron recovery kinetics depend on capillary width, immersion depth, and liquid surface tension. SUSP also demonstrates practical functionalities: it enables efficient underwater bubble collection, directional transport, and reduces hydrodynamic drag by up to 4.3% by preserving a continuous air layer under flow. Even in mud-rich environments, SUSP retains its superhydrophobicity, highlighting its robustness for applications in marine antifouling, drag reduction, and underwater gas management. This work presents a biomimetic, passive strategy for achieving durable and self-replenishing superhydrophobicity in submerged conditions.