Inspired By The Colorful Cotinga Bird, Scientists Attempt To Create Everlasting Color
All around us nature shows us beautiful colors in brilliant hues. A different kind of color, structural color, is formed by microscopic structures that enhance certain colors. From the peacock's iridescent blue to the Morpho butterfly's varied colors, structural color forms when tiny pores on the body interact with light enhancing their color. In a new study, researchers take inspiration from the bright turquoise-blue, spangled cotinga - a bird found in the Amazon - to create artificial structural colors.
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Cells in the cotinga's feathers have a series of fine pores in multiple layers that scatter light so that blues are reflected back to our eyes, even though the pigment in their feathers may be a different color. Therefore, if scientists can recreate the patterns in the feather's pores, they can also artificially create structural colors. They used the cotinga because the pores on its feathers are randomly placed, and are simpler to reconstruct than other naturally occurring structures.
Led by Vinothan N. Manoharan, from the Harvard School of Engineering and Applied Sciences, the researchers tried to give man-made materials structural color. They devised a system in which microcapsules are filled with a disordered solution of even smaller particles suspended in water. When the microcapsule dries out, it shrinks, casing the particles to move closer together. The distance between the particles then creates specific colors.
"There's an average distance between particles, even though there is no ordering in the particles. It's that average distance that is important in determining the color," Manoharan said in a statement.
The study follows another from Yale University in 2009, which used dried aggregates of solid particles to create blues similar to the cotinga's hue. According to Manoharan, the tunable color capsules have huge potential for industrial and commercial applications. A variety of new paints, for example, can be created by using the suspended capsules. "Right now, the red dye, carmine, comes from an insect called a cochineal," Manoharan said. "People would like to move away from that because it's very labor-intensive, and getting that color involves harvesting a lot of insects."
The researchers are also trying to figure out how to keep structural color intact over the course of many years. The cotinga's blue remains bright and vivid for as long as it lives. But in synthetic paints, the color molecules absorb sun's energy and eventually deteriorate.
the potential of structural color to remain intact over years. The cotinga's blue remains bright and vivid for as long as it lives. In synthetic paints, the color molecules absorb the sun's energy and eventually deteriorate. "Most color you get in paints, coatings, or cosmetics, even, comes from the selective absorption and reflection of light," Manoharan said. "What that means is that the material is absorbing some energy, and that means that over time, the material will fade."
The researchers are attempting to create ageless colors that can be used in electronic display technologies like e-readers. The microcapsules could be used in displays that create pixels with colored particles rather than LEDs, liquid crystals, or black-and-white "electronic ink."
"We think it could be possible to create a full-color display that won't fade over time," Manoharan said. "The dream is that you could have a piece of flexible plastic that you can put graphics on in full color and read in bright sunlight."
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