Influences of Heat Treatment, Particle Arrangement, and Binder Addition on the Mechanical Robustness of Structurally Colored Coatings Formed with Monodisperse SiO₂ Spheres

This article highlights the critical factors influencing the mechanical robustness of structurally colored coatings formed as arrays of monodisperse SiO₂ particles. Various types of coatings can be fabricated using electrophoretic deposition (EPD) techniques. Anodic EPD generates coatings with colloidal crystalline structures, iridescent structural color, and noteworthy mechanical robustness owing to interparticle necking during heat treatment, even in the absence of binder additives. Conversely, coatings prepared via cathodic EPD exhibit noniridescent structural color and colloidal amorphous structure, with only marginally improved mechanical robustness after high‐temperature treatment. However, when Mg(OH)₂ is codeposited during EPD in the coating, the resultant film exhibits strong adhesion between particles and the substrate—as evidenced by minimal peeling from the substrate even after ultrasonication for 6 h—owing to the binding effect of MgO, which is converted from Mg(OH)₂ via heat treatment. The robustness of the film is not dictated by the size of the SiO₂ particles, suggesting that this approach can be applied to structurally colored coatings of various colors. Consequently, the results suggest that EPD with the addition of a binder and heat treatment can be used to fabricate particle‐array‐type coatings with extremely high mechanical robustness.