Structurally colored materials consisting of arrays of submicrometer-sized particles have drawn a great deal of attention because of their advantages, including low cost, low impact on human health as well as the environment, and resistance to fading. However, their low thermal stability is considered to be a critical issue for their practical use as colorants. Black-colored substances that can absorb the white color are added to colloidal array-type structurally colored materials to enhance their chromaticity. The poor thermal stability of commonly used black coloring additives, carbon black and Fe3O4 nanoparticles, is a main factor that reduces the heat resistance of structural coloration. Here, we demonstrate the preparation of structurally colored materials with extraordinarily high heat resistance of coloration, up to 900 °C. Several metal oxides, i.e., calcium manganese-based oxide (CCMO), chromium-iron-cobalt-nickel oxide (CFCNO), and lanthanum manganite (LMO), are synthesized and employed as black additives for structurally colored coatings prepared by the electrophoretic deposition of spherical silica particles. When CCMO is used as a black additive, the coloration heat resistance of the film is stable up to 700 °C. On the other hand, the films maintain vivid structural colors after exposure to 900 °C temperatures when CFCNO and LMO are employed as black additives. On the basis of this finding, high heat resistance of structural colors requires both heat resistance of the black additives and nonreactivity with the components of the spherical particles used for colloidal arrays.
Keywords: black metal oxides; electrophoretic deposition; environmentally friendly colorants; structural color; thermal stability.