Tug and twist change color of ‘chameleon’ film

New chameleon-like "skin" changes color when flexed. (Credit: Connie Chang-Hasnain/UC Berkeley)

Engineers have created an ultra-thin film that, when pulled or twisted, can shift colors as easily as a chameleon’s skin.

Researchers say the thin-skinned material could be developed into active camouflage for vehicle exteriors, or a new class of display technologies.

It could also be used as an early warning system for structural fatigue by changing color when critical components on bridges, buildings, or the wings of airplanes are stressed.

Teeny tiny ridges

Instead of using chemical dyes or pigments to absorb and reflect light, engineers manipulated the structure of the material, in this case a film of silicon about a thousand times thinner than a human hair, to do the job.

Rows of tiny ridges—each smaller than a wavelength of light—etched onto the film would reflect light at different wavelengths, depending upon how far about the ridges are spaced.

Tuning the spaces between the ridges allowed the researchers to select specific colors to be reflected. This feature also meant that shifting the spaces between the ridges by flexing or bending the material would lead to a different wavelength of reflected light.

It was only earlier this week that scientists at the University of Geneva revealed how chameleons change colors. The color-shifting lizard changes the spacing  of nanocrystals just under its skin.

“We were fascinated by the chameleon’s ability to change colors, and the process of mimicking their skin has been exciting,” says Connie Chang-Hasnain, professor of electrical engineering and computer sciences at University of California, Berkeley.

“The coolest thing is that you can hold the sample film and stretch it to see the colorful effect.”

The study is published in the journal Optica.

Source: UC Berkeley