Structural Colors in Nature: The Role of Regularity and Irregularity in the Structure

Abstract

Coloring in nature mostly comes from the inherent colors of materials, but it sometimes has a purely physical origin, such as diffraction or interference of light. The latter, called structural color or iridescence, has long been a problem of scientific interest. Recently, structural colors have attracted great interest because their applications have been rapidly progressing in many fields related to vision, such as the paint, automobile, cosmetics, and textile industries. As the research progresses, however, it has become clear that these colors are due to the presence of surprisingly minute microstructures, which are hardly attainable even by ultramodern nanotechnology. Fundamentally, most of the structural colors originate from basic optical processes represented by thin-film interference, multilayer interference, a diffraction grating effect, photonic crystals, light scattering, and so on. However, to enhance the perception of the eyes, natural creatures have produced various designs, in the course of evolution, to fulfill simultaneously high reflectivity in a specific wavelength range and the generation of diffusive light in a wide angular range. At a glance, these two characteristics seem to contradict each other in the usual optical sense, but these seemingly conflicting requirements are realized by combining appropriate amounts of regularity and irregularity of the structure. In this Review, we first explain the fundamental optical properties underlying the structural colors, and then survey these mysteries of nature from the viewpoint of regularity and irregularity of the structure. Finally, we propose a general principle of structural colors based on structural hierarchy and show their up-to-date applications.

Can the narrow red bands of dragonflies be used to perceive wing interference patterns?

“…Optical thin film was described in the seventeenth century by early physicists, for example, Robert Hooke and Isaac Newton (Kinoshita & Yoshioka, 2005). Further advancing the understanding of wave and polarization optics, Augustin‐Jean Fresnel and David Brewster from the eighteenth century provided quantitative equations for reflected intensity from surfaces as a function of incidence angle and polarization.…”

Colors and pterin pigmentation of pierid butterfly wings

“…Butterflies are some of the most eye catching animals, due to their vividly colorful wings, where stacks of colored scales together form patterns, characteristic for each species (Nijhout, 1991;Kinoshita and Yoshioka, 2005). These colors are either due to pigments that absorb light in a restricted part of the visible wavelength range or due to structures that reflect light in a specific wavelength band.…”

“…These colors are either due to pigments that absorb light in a restricted part of the visible wavelength range or due to structures that reflect light in a specific wavelength band. The optics of butterfly coloration is far from understood in detail, however, as almost every species and certainly those in different families apply a variety of optical coloring methods; often pigmentary and structural coloration techniques are combined in a non-trivial way (Kinoshita and Yoshioka, 2005;. Especially in those cases where butterfly scales feature so-called photonic crystals, quantitative descriptions are still in their infancy (Vukusic and Sambles, 2003;Kinoshita and Yoshioka, 2005;Michielsen and Stavenga, 2007).…”

“…The optics of butterfly coloration is far from understood in detail, however, as almost every species and certainly those in different families apply a variety of optical coloring methods; often pigmentary and structural coloration techniques are combined in a non-trivial way (Kinoshita and Yoshioka, 2005;. Especially in those cases where butterfly scales feature so-called photonic crystals, quantitative descriptions are still in their infancy (Vukusic and Sambles, 2003;Kinoshita and Yoshioka, 2005;Michielsen and Stavenga, 2007). For the study of butterfly coloration, a relatively simple and therefore attractive case is presented by members of the Pieridae (Kemp et al, 2005), a family of butterflies that have brightly colored wings, characterized by large, bold patterning.…”

Tunable structural color in organisms and photonic materials for design of bioinspired materials

“…Iridescence is a structural color formed without using pigments, dye or luminescence [1,2]. It originates from spectrally selective reflection of visible light from a periodic modulation of refractive index.…”