Engineers from the University of California at Berkeley in the U.S. have created a thin material which is showing 'chameleon-like' properties. In tests it has been made to change colour, on demand, when stretched or bent with only a small amount of force applied to it. This new material offers possibilities for an entirely new class of display technologies, colour-shifting camouflage, and sensors that can detect otherwise imperceptible defects in buildings, bridges, and aircraft.
The material's colour changes reliably as it is flexed thanks to rows of ridges that are precisely etched onto a silicon film one thousand times thinner than a human hair.
These ridges reflect a specific a wavelength of light, with that wavelength determined by the spaces between the ridges. When the material is flexed or bent, this spacing changes and so too does the color reflected.
"This is the first time anybody has made a flexible chameleon-like skin that can change colour simply by flexing it," said Connie J. Chang-Hasnain, a member of the Berkeley team and co-author on a paper published in
Optica, The Optical Society’s (OSA) journal.
By precisely etching tiny features, smaller than a wavelength of light, onto a silicon film one thousand times thinner than a human hair, the researchers were able to select the range of colors the material would reflect, depending on how it was flexed and bent.
Previous attempts to create flexible colour-shifting surfaces had issues with reliability or control, metallic surfaces reflect only a portion of light received and non-metal surfaces have previously been too thick or rigid. The team behind this new material overcame these issues by embedding its 120 nanometer-thick silicon bars into a flexible layer of silicone.
The result was a skin-like membrane that is easy to manufacture and that reflects precise and pure colours. The membrane changed colour from green to yellow to orange in response to tiny amounts of stretching, just a 25 nm change in the period, or interval, of the ridges corresponded to a 39 nm change in display colour (from 541 to 580 nm wavelength). Further stretching produced additional colours, but beyond this point the efficiency of the material – how much light it reflected – dropped substantially.