Michael Addition Reaction‐Assisted Surface Modification of Melanin Particles for Water‐Repellent Structural Color Coating

Abstract There is significant interest in developing paints based on structural colors, which do not fade like dyes and pigments. To use these paints as coatings, it is necessary to have a technology that can easily impart structural color to the material's surface without changing color based on the viewing angle. In addition, water‐repellent properties that lead to stain resistance are required for practical application. This study applies a structural color coating by synthesizing hydrophobic melanin particles using the Michael addition reaction and arranging these particles on a substrate at high speed. The resulting coating film shows angle‐independent structural color due to the amorphous structure of the particle arrangement, and the color tone could be controlled by adjusting the particle size. The combination of the particle's hydrophobic surface and the microscopic unevenness from the arrangement structure produced a superhydrophobic coating with a contact angle of over 160°. Since the Lotus effect, resulting from superhydrophobic surfaces, can maintain the cleanliness of structural color coatings, the findings of this research will contribute to the development of next‐generation coating technology.