Photonic crystals on wood surfaces: tunable structural colors exhibiting iridescent effects and stimulus responsivity

Photonic crystals (PCs) with periodic nanostructures enable high-quality structural coloration, making them highly suitable for applications in printing and dyeing. However, PC-based structural coloration on wood surfaces remains a challenge. In this work, PCs were successfully constructed on wood (Birch, Betula spp.) surfaces via gravitational deposition, displaying bright, vibrant, and angular-dependent structural colors with stimulus-responsivity to water. Monodisperse polystyrene (PS) microspheres were used as building units. The colors were tunable through precisely modulating the diameter of the PS colloidal microspheres. The stacking configuration of the PS spheres within the interfacial transition region transitions from disordered to ordered. Drying-induced deformation of the micro-nano structures on the wood surface can lead to interfacial defects, such as disordered packing and cracks. Thanks to the water-responsive property of PCs, the coatings show promising potential for application in anti-counterfeiting labels. This work provides methodological and mechanistic insights for structural coloration on wood substrates, while offering many attractive opportunities for biomass materials.