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Engineers at the Massachusetts Institute of Technology recreated a 19th-century photographic technique with an elastic band that changes color when stretched.
The team there says they have developed a scalable manufacturing technique that gives the materials “structural color.” The technology could be used in pressure-controlling bandages, shade-changing fabrics or touch robots.
MIT scientists draw on the work of Gabriel Lippmann, who in 1886 was credited with the first color photograph.
He generated color photos by preparing a very thin clear emulsion glass in front of him, and then he was exposed to light rays that were reflected back through the mirror emulsion. The interference of the incoming and outgoing light waves causes the emulsion’s grains to adjust their position and reflect the pattern and wavelength of the incident light.
This method created structurally colored floral images and other scenes on emulsions. However, the process involves preparing handmade emulsions and waiting for days until the material is sufficiently exposed to light. Due to the laborious nature of the technique, it did not take off. Although Lippmann won the Nobel Prize for his work.
130 years later and MIT researcher Benjamin Miller stumbles upon a holography exhibit at the MIT Museum.
“I realized that what you’re doing in holography is the same thing that nature does with structural paint,” Miller said. MIT News.
The visit led him to research the history of holography and then meet the Franco-Luxembourg physicist Lippmann.
Holography has come a long way since the 1880s, and Miller wondered if he could produce large-scale, structurally colored materials from modern holographic materials. Like Lippmann emulsions, today’s holographic matter consists of light-sensitive molecules that can form colored mirrors when exposed to incoming photons.
The team used a plastic, transparent holographic film and projected images onto it. Instead of taking days, the film produced large and detailed images in minutes, extracting vivid colors from the original images.
Then the film can be peeled off and as it is stretched, it changes color. Its nanoscale structures are reconfigured to reflect slightly different wavelengths, appearing red and then blue when pushed and pulled.
Real world uses
Color-changing material is easily incorporated into fabric, but can also be used in bandages. For example, when putting a bandage on an injured arm, the color can indicate the correct tightness.
Image Credits: All photos courtesy of MIT.
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