Scientists have created a new light-activated ink that can change color on demand. It consists of differently colored microbeads that rise or sink in response to different wavelengths of light, so that its surface takes on a specific color, which could be useful for new types of electronic displays or active camouflage systems.
Cephalopods such as octopuses and squid are known for their ability to change color, and they do so using organs called chromatophores. They consist of tiny pigment sacs that can expand or contract at will, and the combination of colored pigments that are visible or hidden at any given time give the animal’s skin a specific color or pattern.
This complex natural mechanism has inspired researchers at the University of Hong Kong, Xiamen University and Hong Kong University of Science and Technology to create a new color-changing ink.
This ink contains microbeads made of titanium dioxide and dyed cyan, magenta and yellow. You might think of this trio as the core ink colors of some printing systems, thanks to their ability to reproduce other colors in various combinations. That force is at play here, too.
In this case, microbeads are mixed together in equal amounts and designed in different colors to rise to the surface or sink to the bottom in response to light. By adjusting the wavelength and intensity of light, surfaces can be tinted in various colors through the same combined effect, creating patterns or even images.
The trick is the titanium dioxide in the beads, which creates a redox reaction in response to light sending the beads in different directions. Each dye color responds to a different wavelength of light, sending beads of that color up or down. For example, green light will bring yellow and cyan beads to the surface, making them appear green, while magenta beads sink to the bottom. In tests, the team demonstrated that the system was able to reproduce a series of images projected on a surface.
However, there are some caveats. For one thing, its exact function in daylight or ambient light remains to be seen. Color reproduction and brightness may need some tweaking, and the team says switching images and colors is rather slow. But these are areas that will be explored in future work, and if successful, the technique could be used to create new types of displays, e-ink devices, and even active optical camouflage.
The study was published in the journal nature.
source: Hong Kong university