Vibrant bird feathers inspire new artificial colours and light control

Vivid colour in nature such as that in a peacock’s tail or a beetle’s shell often results from tiny biological structures which affect the reflection of light. This is called “structural colour” and can be useful in the reproduction and defence of plants and animals.

Structural colour arises due to tiny structured surfaces, fine enough to interfere with the passage of light. It was first observed by Isaac Newton and Robert Hooke and is based on the principle of wave interference.

Biological diffraction gratings, crystal fibres, selective mirrors and structures within plant cells are some of the means by which reflections from multiple surfaces of thin films can be made to interfere.

A team of researchers based at Nagoya University, Japan, were inspired by the structural colour of the plumage of Stellar’s jay, a common North American bird with vibrant cobalt feathers in its lower body and tail.

“The Stellar’s jay’s feathers provide an excellent example of angle-independent structural colour,” said Professor Yukikazu Takeoka, associate professor in Nagoya’s department of molecular and macromolecular chemistry and author of the study.

“This colour is enhanced by dark materials, which in this case can be attributed to black melanin particles in the feathers.”

For most of these materials, the reflected light interferes to create different colours at different angles. However, in Stellar’s jay, the blue colour appears not to change. This is because the microscopic structures sit on top of unusual black particles that absorb some light.

To recreate the spongy texture within the bird’s feathers, the researchers used black particles as the “core” of the material. These were surrounded with layers of transparent particles to create blackberry-like structures. The size of the cores and the thickness of the layers control the resulting colour and saturation.

Reproducing the structure in the laboratory resulted in a new type of artificial pigment.

“Our work represents a much more efficient way to design artificially produced angle-independent structural colours,” said Professor Takeoka.

Being able to harness structural colouration could allow engineers to create new materials with applications in solar cells, low-reflectance glass and adaptive camouflage.

“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.”