AsianScientist (Mar. 24, 2014) – Researchers from Harvard University and Korea Advanced Institute of Science and Technology (KAIST) have come up with nanoparticle-based colors that could replace traditional pigments.
Most of the colors we see around us arise from paints and dyes that absorb certain wavelengths of light and reflect the remainder. In contrast, structural color is created when an object’s very nanostructure amplifies a specific wavelength.
Although examples of structural color have been found in nature, producing structural color in the lab is difficult as it requires a material’s molecules to be in a very specific crystalline pattern.
Taking a different approach inspired by the feathers of the cotinga bird, researchers have devised a system to obtain structural color using microcapsules filled with a disordered solution of nanoparticles suspended in water. When the microcapsule is partly dried out, it shrinks, bringing the particles closer and closer together. Eventually the average distance between all the particles will give rise to a specific reflected color from the capsule.
“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,” said Professor Vinothan N. Manoharan, lead author of the study.
The tunable color capsules present interesting technological opportunities, said Manoharan. For example, a whole spectrum of new paints might be created using suspended capsules.
“Right now, the red dye carmine comes from an insect called a cochineal,” he 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 capsules might also offer a safety advantage. The reason for using natural dyes like carmine is that many synthetic dyes are toxic. The new color capsules can be made with particles of almost any material in the right structural formation, so toxicity can be easily avoided.
Most compelling of all, however, is that some structural colors found in nature can last indefinitely as long as the colored object remains intact.
“Most color you get in paints, coatings or cosmetics, even, comes from the selective absorption and reflection of light. What that means is that the material is absorbing some energy, and that means that over time, the material will fade,” said Manoharan.
The sun’s energy pummels the molecules in conventional pigments. Eventually, the molecules simply deteriorate and no longer absorb the colors they used to, leading to sun bleaching. The researchers are currently testing their innovation to see if it can create an effectively ageless color.
Electronic display technology might also benefit from this advance. 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,” said Manoharan. “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.”
The article can be found at: Park et al. (2014) Full-Spectrum Photonic Pigments with Non-iridescent Structural Colors through Colloidal Assembly.
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Source: Harvard; Photo: albastrica mititica/Flickr/CC.
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