Bio‐Inspired Bright Structurally Colored Colloidal Amorphous Array Enhanced by Controlling Thickness and Black Background

Abstract

Inspired by Steller's jay, which displays angle-independent structural colors, angle-independent structurally colored materials are created, which are composed of amorphous arrays of submicrometer-sized fine spherical silica colloidal particles. When the colloidal amorphous arrays are thick, they do not appear colorful but almost white. However, the saturation of the structural color can be increased by (i) appropriately controlling the thickness of the array and (ii) placing the black background substrate. This is similar in the case of the blue feather of Steller's jay. Based on the knowledge gained through the biomimicry of structural colored materials, colloidal amorphous arrays on the surface of a black particle as the core particle are also prepared as colorful photonic pigments. Moreover, a structural color on-off system is successfully built by controlling the background brightness of the colloidal amorphous arrays.

Effects of multiple scattering on angle-independent structural color in disordered colloidal materials

“…Angleindependent structural colors appear matte and homogeneous, often indistinguishable from colors that come from absorbing pigments. This type of coloration is found in many species of birds [2][3][4][5][6][7][8][9] and has been mimicked in disordered assemblies of colloidal particles [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29].…”

Self-assembled colloidal arrays for structural color

“…A large area of uniform PAS membranes was obtained by depositing alternating layers of charged colloidal particles and layers of an oppositely charged polyelectrolyte. 76 By using nonuniform particles for the colloidal assembly, the tendency for colloidal crystallization during the selfassembly process could be considerably suppressed, which favors the formation of 3D PASs. In this regard, Lai et al 77 dispersed nonuniform SiO 2 particles constructing a photocurable PAS resin in the resin prepolymer.…”

Bioinspired Color Materials Combining Structural, Dye, and Background Colors

“…As a result, stimuli‐responsive, structural color materials can be created . Additionally, understanding the coloring mechanisms of these color materials has clearly shown that the background color is also important for creating colorful color materials . Generally, additive and subtractive color mixing reproduce colors.…”

“…When the background was white, the reflection intensity from the background was high for the entire visible region, and the PBG due to the Bragg reflection from the colloidal crystals could not be observed in the spherical colloidal crystal reflection spectra (Figure b). [4a] As a result, observing the structural color arising from the spherical colloidal crystals was difficult, and the spherical colloidal crystals appeared as a white powder. For the reflection spectra measured with a black background, the influence of the background light disappeared, and the PBG was clearly observed (Figure c).…”

“…Because spherical colloidal crystals with large sizes are greatly affected by incoherent multiple scattering, the reflectance in the visible‐light region is high, even if the background is black. [4a] As a result, as shown in Figure a, vivid colors are less likely to be observed from larger spherical colloidal crystals.…”