Biomimicry with Artificial Structural Colors

Bio-inspired bright structurally colored colloidal amorphous array enhanced by controlling thickness and black background. (Source: Y. Takeoka)

Bright colors in the natural world often result from tiny structures in feathers or wings that change the way light behaves when it’s reflected. This structural color is respon­sible for the vivid hues of birds and butter­flies. Arti­ficially harnessing this effect could allow us to engineer new materials for appli­cations such as solar cells and chame­leon-like adap­tive camou­flage.

Inspired by the deep blue colora­tion of a native North American bird, Stellar’s jay, a team at Nagoya Uni­versity reproduced the color in their lab, giving rise to a new type of arti­ficial pigment. “The Stellar’s jay’s feathers provide an excellent example of angle-inde­pendent structural color,” says Yukikazu Takeoka, “This color is enhanced by dark materials, which in this case can be attri­buted to black melanin particles in the feathers.”

In most cases, structural colors appear to change when viewed from dif­ferent per­spectives. For example, imagine the way that the colors on the under­side of a CD appear to shift when the disc is viewed from a dif­ferent angle. The dif­ference in Stellar’s jay’s blue is that the structures, which inter­fere with light, sit on top of black par­ticles that can absorb a part of this light. This means that at all angles, however you look at it, the color of the Stellar’s Jay does not change.

The team used a “layer-by-layer” approach to build up films of fine par­ticles that recreated the micro­scopic sponge-like texture and black backing particles of the bird’s feathers. To mimic the feathers, the researchers covered micro­scopic black core par­ticles with layers of even smaller transpa­rent particles, to make rasp­berry-like particles. The size of the core and the thick­ness of the layers controlled the color and satu­ration of the resul­ting pigments. Impor­tantly, the color of these particles did not change with viewing angle.

“Our work represents a much more efficient way to design arti­ficially produced angle-inde­pendent structural colors,” Takeoka adds. “We still have much to learn from biological systems, but if we can under­stand and success­fully apply these phenomena, a whole range of new meta­materials will be acces­sible for all kinds of advanced appli­cations where inter­actions with light are important.” (Source: Nagoya U.)

Reference: M. Iwata et al.: Bio-Inspired Bright Structurally Colored Colloidal Amorphous Array Enhanced by Controlling Thickness and Black Background, Adv. Mat., online 26 April 2017; DOI: 10.1002/adma.201605050

Link: Dept. of Molecular Design and Engineering, Nagoya University, Nagoya, Japan

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