Hydrophobicity of golden-phase leaves coated with zinc oxide-based nanocomposite for decorative local products

Golden-phase leaves are widely used in decorative crafts and heritage products, yet their susceptibility to moisture limits long-term durability, especially in humid environments. This study investigates the wetting behaviour of zinc oxide (ZnO)-based nanocomposite coatings designed to preserve the hydrophobicity and service life of golden-phase leaves. The uncoated leaf exhibits strong intrinsic water repellency, with a water contact angle of 151°, attributed to hierarchical surface roughness that supports a Cassie–Baxter-like wetting regime. However, probe liquids with lower surface tension show reduced contact angles, indicating partial transitions toward Wenzel-like wetting. To compare three coating formulations, ZnO/chitosan (brush), ZnO/polyvinyl alcohol (PVA) (spray), and ZnO/chitosan/PVA (spray) were prepared and evaluated. The binary coatings decreased water contact angles to below 85° due to the hydrophilicity of chitosan and PVA. In contrast, the ternary ZnO/chitosan/PVA coating produced a high water contact angle of 136° and an exceptionally low surface free energy of 2.4 mN/m, tend to suppress liquid infiltration. The results demonstrate that the ZnO/chitosan/PVA coating applied by a simple spray process, alters the apparent wetting behavior of a naturally hierarchical biological substrate. This experimental observation of wettability enhancement on a natural surface complex morphology-dominated is relevant to preservation of decorative natural materials.