Enhancing the brightness and saturation of noniridescent structural colors by optimizing the grain size

Using structural colors instead of pigment colors has many advantages, both environmentally and economically. However, the traditional process of eliminating structural iridescence often causes a decrease in color brightness and saturation. For a periodic optical structure having a refractive-index difference, it is necessary to pile up a certain number of layers to make the maximum reflectivity reach almost unity and obtain the minimal bandwidth. Therefore, the amorphization process inevitably leads to a decrease in the brightness and saturation of the structural color, as the short-range order domain is too small. In this paper, the concept of the polycrystallization process and corresponding method are introduced, by which a polycrystalline structure with an optimal grain size is built using silica nano-spheres. This structure guarantees the best brightness and saturation of the color at a low viewing angle, while eliminating the reflection of other colors at a high viewing angle. Subsequent graphene doping and superhydrophobic treatment enable the structural color to maintain its brilliant color for a long time even in an intensive harsh environment, such as on white substrates under high humidity conditions.