Non-iridescent structural color inspired by tarantulas

What is it about?

Photonic structures with long-range order are inherently iridescent, suggesting by current theory. Contrary to this paradigm and inspired by biological photonic structures from hairs of blue tarantulas, a noniridescent photonic structure with long-range order is shown here. This photonic structure is hierarchical and has high degrees of rotational symmetry in suitable spatial scales.

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Why is it important?

Structural color is produced by optical effects when light interacts with nanostructures that are about the same size as the wavelength of light. Structural colors are more vibrant and durable than the pigments used in most human-made products. However, most structural colors are strongly iridescent so that they change color when looked at from different directions. While eye-catching, iridescence prohibits a broader usage of structural color in our daily life, as in most applications we want the colors to remain faithful. Amorphous structures can produce non-iridescent structural colors, however, they are hard to manufacture. In contrast, highly periodic designs are easy to manufacture and make vibrant structural colors, but they also result in strong iridescence. In short, non-iridescent structural color is hard to come by. Now, this research on tarantulas may help to solve this vexing problem. The researchers first discovered that many vibrant blue tarantulas do not show iridescence even though the spiders use nanostructures to produce those (structural) colors. As they dug deeper, the researchers found that the hairs of some species of blue tarantulas show a special flower-like shape that they hypothesized reduced the iridescent effect resulting from periodic structures. To test this hypothesis, the researchers decomposed the effect of each design component of the hairs using a series of computer simulations and physical prototypes built using a cutting-edge nano-3D printing technology. In the end, the researchers almost completely eliminated iridescence using a highly periodic but non-iridescent structure with the flower-like shape seen in tarantulas. The color produced by the 3D printed structures has a viewing angle of 160 degrees, the largest viewing angle of any synthetic structural colors demonstrated so far! This discovery greatly enhances the potential application of structural color in display screens and other optical devices. "This is a key first step towards a future where "structural colorants" replace the toxic pigments and dyes that are currently used in textile, packaging, and cosmetic industries".