Nature-inspired trapped air cushion surfaces for environmentally sustainable antibiofouling

Feathers of seabirds and waterfowl (for example the mallard duck (Anas platyrhynchos)) consist of hierarchical fibrillar structures encapsulated with hydrophobic preen oil. These characteristics afford waterproofing through the entrapment of air pockets, enabling swimming and diving for such bird species. This liquid repellency mechanism for bird feathers is mimicked by surface hydrophobisation of fibrous nonwoven polypropylene textiles to create large volumes of trapped air at the solid-liquid interface (plastron). Higher static water contact angle values correlate to a greater resistance towards water ingress (akin to the behaviour of mallard feathers). In order to extend the trapped gas layer lifetimes, the transportation of air from the water surface to a submerged air bubble by the diving bell spider (Argyroneta aquatica) for respiration is mimicked via short duration (< 1 s) solar-powered air bubble bursts once every 2 h. This combination of ornithological and arachnological inspired approaches yields stable trapped gas layers at the solid-liquid interface which are shown to inhibit biofouling in real-world outdoor wet environments.