Wood that bounces water off like rubber

The team started by soaking pine cubes in a low-cost room-temperature-vulcanising (RTV) silicone cocktail containing vinyl-triethoxysilane (VTES) and the cross-linker TEOS. Alcoholysis between RTV hydroxyls and ethoxy groups builds a flexible Si–O–Si network whose elastic modulus drops slightly but whose hardness rises 50 %, as nano-indentation reveals. Into this cushioned scaffold they grow ZnO nanorod arrays 5 µm long by a seed-hydrothermal route; rods anchor covalently through Si–O–Zn bridges, forming a micro/nano topography with a 5:1 aspect ratio. The rods’ tips poke above the silicone like miniature pikes, trapping air pockets that force water into a Cassie–Baxter state where droplets skate off at sliding angles below 10°.
Mechanical abuse tells the story: after 400 cm of 1200-grit sandpaper and a 2 kg load, contact angles still exceed 140° because fractured rods absorb energy while the elastomer underneath relaxes back, preserving roughness. XPS mapping shows Zn content on the surface drops 30 %—proof the sacrificial layer is doing its job—yet water repellence holds. Likewise, a 60 mL min⁻¹ water jet fired for 66 h removes only outermost nanorods; the underlying lattice keeps droplets bouncing, as high-speed video confirms. Even 1000 cycles of aggressive tape peel, simulating wind-blown debris, cannot expose bare wood.
Chemical warfare fares no better: dipping samples for 30 h in pH 1 hydrochloric acid or pH 13 sodium hydroxide leaves superhydrophobicity intact, whereas conventional silica-nanoparticle coatings collapse within hours. UV-A lamps at 340 nm for 33 days bleach untreated pine to a colour difference ΔE of 18; the modified face shifts only 1 unit, thanks to ZnO’s inherent UV-screening and the silicone’s visible-light reflectance. Water absorption plummets from 64 % to 7 % after two hours immersion, cutting volumetric swelling by half and delivering an anti-swelling efficiency of 56 %—critical for decking or cladding that sees rain and sun in quick succession.
The process uses no fluorine, needs only ambient curing, and works on six species—from balsa to fir—suggesting mills could retrofit existing dipping lines. With global demand for durable bio-based building materials rising, a timber that cleans itself, rejects graffiti and never needs re-sealing could command premium prices while keeping 70 million tonnes of lignin waste out of furnaces. The authors are now scaling to metre-long boards and accelerated weather chambers that mimic monsoon cycles, but they say the chemistry is ready: just dip, dry, and let the wood take the beating instead of the coating.

See the article:

DOI

https://doi.org/10.1016/j.jobab.2025.11.004

Original Source URL

https://www.sciencedirect.com/science/article/pii/S2369969825000830

Journal

Journal of Bioresources and Bioproducts