Reversibly photochromic wood constructed by electric field-assisted self-assembled chitosan and tungsten trioxide coatings

The photochromic properties are highly desirable for advanced wood applications, but they have not been extensively studied. To incorporate photochromic capabilities into wood materials, composite coatings were developed on the wood surface using an electric field-assisted layer-by-layer (LBL) self-assembly technique. The composite coatings consist of cationic chitosan and anionic tungsten trioxide (WO3) nanoparticles. By applying a direct current voltage during the deposition process, a well-organized distribution of WO3 nanoparticles was achieved, resulting in a uniform coverage of the wood substrate. This assembly process facilitated the creation of structured photochromic coatings with minimal nanoparticle fillers, a straightforward and rapid procedure, and potential for large-scale production. Lab colorimetric results demonstrated that the wooden substrate changed color from its natural state to blue when exposed to UV light. UV-vis spectroscopy further confirmed the efficient absorption of WO3 and photochromic properties of the modified wood.