Color-changing material could protect against counterfeiting

New materials are changing the way people interact with their environment. The most recent addition: An ultra-thin chameleon-like material that changes color when a tiny amount of pressure is applied or slight stretching occurs. The material offers exciting possibilities in the world of packaging and smart labeling, as Dr. Connie Chang-Hasnain of the University of California Berkeley’s Department of Electrical Engineering and Computer Science explains.

“The color of this new material is very sensitive to mechanical deformation such as bending, twisting, and stretching”, says Dr. Chang-Hasnain in an email interview. “Therefore, it can represent the structural change simply by a change in color. This method provides a straightforward way to detect any damage without requiring any additional testing equipment.”

In most materials, the sensation of color is created by the chemical composition of the surface that absorbs and reflects specific wavelengths of the visible spectrum of light. When shorter wavelengths are reflected, a reddish color appears, longer wavelengths are perceived as having bluish tint. New materials such as the ultra-thin film created by the team working with Dr. Chang-Hasnain are able to change colors without chemical pigments or dyes.

The scientists created tiny structures on the surface of the new material by etching rows of ridges onto a single semiconductor layer of silicon 120 nanometers thick. Each ridge reflects a certain wavelength of light. The spacing of the rows and ridges determines the color they reflect and any deformation such as bending, flexing or stretching results in a change of color. The semiconductor material also allowed the team to create a skin that was incredibly thin, perfectly flat, and easy to manufacture with the desired surface properties.

“The key component of this material is the nanostructure embedded in the polymer, while the type of polymer can vary depending on the applications. For example, instead of PDMS (polydimethylsiloxane), plastic film can be used for food packaging”, says Dr. Chang-Hasnain. There are many potential applications: “This new material-of-many-colors offers intriguing possibilities for an entirely new class of display technologies, color-shifting camouflage, and sensors that can detect otherwise imperceptible defects in buildings, bridges, and aircrafts”, explains the lead researcher. “Smart labeling is an interesting application. Because the material can have very unique color-coding, it is promising for anti-counterfeiting”, she says.

Because of its unique properties, Dr. Chang-Hasnain sees additional applications once the material is produced on a larger scale: “This chameleon material could also be used in a new class of display technologies, adding brilliant color presentations to outdoor entertainment venues”, she says. “It also may be possible to create an active camouflage on the exterior of vehicles that would change color to better match the surrounding environment.” Dr. Chang-Hasnain also foresees uses in more common, day-to-day applications, for example in sensors that would change color when critical components of buildings or vehicles experienced structural stress.