NANOSTRUCTURED CAPSULES COULD BRING ABOUT PAINTS AND ELECTRONIC DISPLAYS THAT NEVER FADE
Among the taxidermal specimens in Harvard’s Museum of Comparative Zoology, past centuries-old fur coats, arises a flicker of brilliant blue. This is the spangled cotinga. Surprisingly, the cotinga is about as old as everything in the room, but its color is still as dazzling as the day it was brought to the museum. The cotinga—or rather its feathers—achieve this effect through structural color.
Unlike color that we usually think of, which arises from paints and dyes absorbing certain wavelengths of light and reflecting the remainder, structural color is created when an object’s very nanostructure amplifies a specific wavelength. Cells in the cotinga’s feathers have a series of tiny pores spaced just right so that blues (and not much of anything else) are reflected back to our eyes. Because of this, if the feathers were thoroughly pulverized, the formation of pores and therefore the color would be lost. It also means that the same color could be produced from an entirely different material, if one could recreate the same pattern made by the feathers’ pores.
Researchers led by Vinothan N. Manoharan at the Harvard School of Engineering and Applied Sciences want to recreate this effect, giving man-made materials structural color. Producing structural color is not easy, though; it often requires a material’s molecules to be in a very specific crystalline pattern, like the natural structure of an opal, which reflects a wide array of colors. But the pores on the cotinga’s feathers lack a regular order and are therefore a prime target for imitation.
Manoharan’s lab has devised a system where microcapsules are filled with a disordered solution of even smaller particles 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. Shrink the capsule a bit more, and they become another color, and then another.
“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,” says Manoharan, Gordon McKay Professor of Chemical Engineering and Professor of Physics at Harvard.
The current project expands on research conducted at Yale University in 2009, which aimed to mimic the cotinga’s hue and showed that dried aggregates of solid particles could create blues. Jin-Gyu Park was a postdoctoral researcher there and is now a research associate in Manoharan’s group at Harvard SEAS, which specializes in the physics of colloidal suspensions. With Park as lead author, the new paper demonstrates the production of colors across the spectrum, and the new encapsulation system.
The tunable color capsules present interesting technological opportunities, says 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,” says Manoharan. “People would like to move away from that because it’s very labor-intensive, and getting that color involves harvesting a lot of insects.”
Rather than harvesting from nature or preparing specialty chemicals, one for each color, these capsules could provide a universal and direct path to any desired color.
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,” says 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. Manoharan’s group is currently testing their innovation to see if it can create an effectively ageless color.
Electronic display technology—for example, e-readers—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,” says 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 Latest on: Structural color
via Google News
The Latest on: Structural color
- In Light Of George Floyd Protests, A Look At Housing Inequalityon June 3, 2020 at 8:20 am
Many facets of the ingrained social injustice and racial inequality protesters are bemoaning stem from the country’s housing system, which for decades has discriminated against renters and homeowners ...
- Racial Disparities Making Pandemic Worse for People of Color in RI: Health Officialon June 2, 2020 at 8:14 pm
Rhode Island’s top health official on Tuesday said racism over multiple generations has made the coronavirus outbreak worse for residents of color, as the nation grapples with the issue of racial ...
- Is Minneapolis prepared to dismantle — not just acknowledge — structural racism?on June 1, 2020 at 7:58 am
It is important to remember that the killing of George Floyd happened in Minneapolis, a city with its own particular history of racism.
- Price addresses events in Minneapolis, condemns 'disparities of justice' and structural racism in statementon May 30, 2020 at 9:11 pm
President Vincent Price addressed recent events in Minneapolis and condemned “fundamental and systematic disparities of justice” in the United States in a Saturday statement. He acknowledged the ...
- Pointing to George Floyd Death, NY Defense Lawyers' Group Calls for 'Structural Work' in Legal Systemon May 29, 2020 at 3:18 pm
We know what we are seeing when we watch a police officer slowly squeeze a black man’s life away in broad daylight, amid a circle of helpless onlookers,” wrote the New York State Association of ...
- Officials say African-Americans disproportionately affected by COVID-19 because of structural racismon May 29, 2020 at 1:04 pm
Officials say the disproportionate impact of COVID-19 on African-Americans can’t be addressed without first acknowledging the racism they face and the effect that has on their health.
- Support Grows for California Bill Giving Voters Power to Expand Opportunity for Women, People of Coloron May 28, 2020 at 8:11 am
Support Grows for California Bill Giving Voters Power to Expand Opportunity for Women, People of ColorPR NewswireOAKLAND, Calif.Assembly Constitutional Amendment No.
- Testimony: The Disproportionate Impact of COVID-19 on Communities of Coloron May 27, 2020 at 1:04 pm
Statement of the American Hospital Association for the Committee on Ways and Means of the U.S. House of Representatives “The Disproportionate Impact of COVID-19 on Communities of Color” May 27, 2020 ...
- True colors: Using X-rays to trace the evolution of insects' structural colorson May 19, 2020 at 9:14 am
What they discovered, according to Vinod Kumar Saranathan, an assistant professor of life sciences at Yale-NUS College in Singapore, was that the blue and green structural colors they studied had not ...
- True colors: Using X-rays to trace the evolution of insects' structural colorson May 18, 2020 at 7:38 am
What they discovered, according to Vinod Kumar Saranathan, an assistant professor of life sciences at Yale-NUS College in Singapore, was that the blue and green structural colors they studied had ...
via Bing News