Image 1: Professor Mohan Srinivasarao holds a collection of beetles and points to the jeweled beetle Chrysina gloriosa. C. gloriosa was the subject of research by Srinivasarao and his team at the Georgia Institute of Technology in which they studied the surface structures on the beetles' shells and discovered that the iridescent colors are produced from liquid crystalline material that self-assembles into a complex arrangement of polygonal shapes.
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Mohan Srinivasarao, a professor at the School of Polymer, Textile and Fiber Engineering at Georgia Tech, received a grant from the National Science Foundation (NSF) to study what gives the jeweled beetle's shell its iridescence. It is the interaction of light with physical structures on their external surfaces that gives creatures like iridescent beetles, butterflies, certain sea organisms and many birds their unique colors.
Srinivasarao worked with colleagues Vivek Sharma, Matija Crne and Jung Ok Park to study the surface structures on the shells. The team published a detailed analysis in Science magazine of how the jeweled beetle Chrysina gloriosa uses a helical structure that reflects light of two specific colors, and of only one polarization--left circular polarization, to create their striking colors. The reflecting structures used by the beetle consist predominately of three different polygonal shapes--hexagons, pentagons and heptagons, each less than 10 microns in size--whose percentages vary with the curvature of the insect's shell.
"This is really a pattern formation issue," said Srinivasarao. "It is difficult to pack only hexagons onto a curved surface. On flat surfaces, there are fewer defects in the form of five- and seven-sided cells."
Srinivasarao believes the patterns are due to the nature of the cholesteric liquid crystal and because the liquid crystal phase structures itself at the interface between air and fluid. "We think these patterns result because the liquid crystal must have defects on the surface when exposed to air, and those defects create the patterns in the beetle's shell or exoskeleton," says Srinivasarao.
Studying these shimmery shells may lead to new insights into liquid crystal technology. "Understanding how these structures give rise to the stunning colors we see in nature could benefit the quest for miniature optical devices and photonics," said Srinivasarao. Liquid crystalline materials have many uses, from displays for laptop computers to portable music players and other devices to children's thermometers.
This information was taken from the Georgia Tech news release "Jeweled Beetles: Scientists Unlock Optical and Liquid Crystal Secrets of Iridescent Metallic Green Insects." The full story is available Here.
Or, to learn more, view the NSF presentation "Inside a Beetle's Iridescence." [Research supported by NSF grant DMR 07-06235.] (Date of Image: July 2009)
Credit: Georgia Tech; photo by Gary Meek