Robust, biomimetic, superhydrophobic coating with flame-retardant properties and excellent self-extinguishing performance

Flame-retardant coatings are crucial for safety. However, flame-retardant materials are often hydrophilic, causing them to easily dissolve in high-humidity environments, thereby significantly limiting their durability. Thus, the integration of water  repellency and flame retardancy into a single coating is ideal for developing durable, flame-retardant materials. In this study, a robust skin-inspired double-layer coating was fabricated by using spray coating. An intumescent flame-retardant “dermis” layer, comprising ammonium polyphosphate (APP), polydopamine (PDA), and 1-[3-(trimethoxysilyl)propyl]urea (UPTMS), provides the primary heat insulation and flame retardancy functions. A superhydrophobic “epidermis” layer, constructed using silicone nanofilaments (Si NFs), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), and Triethoxy-1H,1H,2H,2H-heptadecafluorodecylsilane (PFDTS), protects flame-retardant materials in moist conditions. Owing to its intumescent effect, the obtained coating demonstrated excellent flame retardancy, with the fire self-extinguishing immediately after the removal of flame source. It achieves a limiting oxygen index (LOI) of 85.3% and significantly decreases the peak heat release rate (PHRR) and the fire growth index (FGI) of 59.20 kW·m^-2 and 0.789 kW·m^-2·s^-1, respectively. The epidermal layer demonstrated outstanding superhydrophobicity and remarkable mechanical stability, with the water contact angle remaining above 160° after 1000 bending cycles between 90° and 180°. Together with the facile spray-coating process, the biomimetic design of this intumescent flame-retardant and superhydrophobic coating provides a feasible and sustainable strategy for constructing durable fireproofing materials.