
Asian Scientist (Jul. 18, 2013) – An examination of the nano-structures present in butterfly wings has uncovered how subtle differences in the tiny crystals on the wings create the stunningly varied patterns of color that butterflies display.
Butterflies display some of the most striking colors found in the natural world, their brightly colored wings shimmering and changing colors as they fly from flower to flower.
Scientists have known for some time that butterfly wings contain nano-structures that give rise to optical effects such as iridescence, the effect of changing color when viewed from different angles. However, it was not fully understood how these structures give rise to the myriad of vivid colors found in different butterfly species, with stunning differences even within the same genus or family.
Now, in a study published in Optical Materials Express, physicists and butterfly researchers have teamed up to investigate the color-creating mechanisms in multiple butterfly species within the Papilio genus.
The three tropical butterfly species the researchers studied all display iridescence, but they do so with different colors: Papilio ulysses, the Ulysses butterfly or blue mountain swallowtail, appears bluish green when seen from above. Its cousin Papilio peranthus, by contrast, looks yellowish green from above, and Papilio blumei, the green swallowtail, is more of a deep green. All three species shift toward deep blue when viewed from a sharp angle.
The discovery could lead to new nature-inspired coatings that can change color by design, if researchers can figure out how to replicate the wings’ light-manipulating properties.
To probe the physics behind the wings’ structural coloration, the scientists examined a cross-section of each species’ wing under a scanning electron microscope. The team found that the wings contain specialized architectures in which solid flat layers known as cuticles alternate with thin “air” layers known as laminae.
The laminae aren’t entirely empty space, however; they also contain pillars of the cuticle material, which gives the wing a repeating crystal-like structure. This structure is similar to what is known as a Bragg reflector—essentially a multi-layered mirror that reflects only certain wavelengths, or colors, of light.
The researchers then measured the light spectrum reflected from the wing at different angles and found that the varying colors of the three species’ wings arise from slight differences in crystal parameters.
P. ulysses has seven cuticle layers, for example, while P. peranthus has eight. The thicknesses of the cuticles and air layers also vary between species. Even though these differences are slight, they have a major effect on the butterflies’ appearance.
According to Kok Wai Cheah, a member of the research team, the lessons learned from Papilio butterfly wings could lead to designer materials that wouldn’t need to be painted or dyed one specific color. The same article of clothing, for example, could reflect a subdued color during the workday, and a more ostentatious one at night.
“You would just tune your structure to produce the color you want,” said Cheah.
The team next plans to investigate color-generating mechanisms in other insect body structures, such as the metallic effect produced by iridescent beetle shells.
The article can be found at: Tam et al. (2013) Iridescence And Nano-Structure Differences In Papilio Butterflies.
——
Source: Optical Society of America; Photo: Johan J.Ingles-Le Nobel/Flickr.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.