The chameleon, as a particularly unique species among reptiles, has always attracted many people to conduct long-term observation and research on its color-changing ability. And the peculiar color-changing ability of their skin has also brought innovative inspiration to humans in some application fields. Although it is currently not realistic for people to change their own skin color to camouflage themselves in the environment, for inanimate objects, this is no longer a problem.
A research team from the Computer Science and Artificial Intelligence Laboratory (CSAIL) at the Massachusetts Institute of Technology (MIT) has created a new type of reusable-programmable “ink” that allows objects to change their color using light. In the future, “the colorful black” may no longer be just a joke.
The research team at MIT has taken a step closer to achieving the ability of chameleons by designing a system called “PhotoChromeleon” (photochromic). This system uses a mixture of photochromic dyes as “ink”, which can be sprayed onto the surface of any object and change its color through the irradiation of ultraviolet or visible light. What’s more, this color-changing process is completely reversible and can be repeated infinitely.
The researchers stated that PhotoChromeleon can be used to customize any product, whether it is a mobile phone case, sports shoes, small daily items, or the surface of large equipment such as cars and airplanes, as long as the customer has updated requirements for color and design. This system can make your items “change every day”. Moreover, these colors do not fade in the natural environment.
The research team demonstrated the system on a shoe, a mobile phone case, a car model, and a small chameleon toy. The time it takes to “draw” patterns on the surface of the object varies from 15 minutes to 40 minutes depending on the shape and orientation of the object. All the patterns have high resolution and can be completely erased at will without leaving any trace; or they can be changed to other patterns at will.
The team created this ink by mixing cyan, magenta, and yellow (CMY) photochromic dyes into a sprayable solution. CMY represents the subtractive color mixing mode because it reduces the reflected light required for the visual system to recognize colors.
Specifically, the researchers used three different wavelengths of light to eliminate each primary color separately. For example, if blue light is used, most of it will be absorbed by the yellow dye and lose its activity, while magenta and cyan will remain, thus producing blue; if green light is used, the magenta dye will absorb and deactivate it, and finally yellow and cyan will remain, and produce green.
After applying this solution to the surface of the object, users only need to place the object in a box with a projector and ultraviolet (UV) light to wait for the pattern to form. The UV light will change the color from transparent to fully saturated, and the projector will reduce the saturation of the color as needed. Once the light activates the color, the new pattern will appear.
If you are not satisfied with the designed pattern, it is very simple to do – just use UV light to erase it, and then you can start designing again.
The PhotoChromeleon system evolved from the previous ColorMod technology of the research team. This technology enables 3D-printed components to change color after being printed. They focused on the research of using ultraviolet-sensitive dyes at that time. However, due to the limitations of the ColorMod project, such as limited color combinations and low resolution of the patterns, the research team decided to further explore ultraviolet-sensitive ink. Using the ColorMod technology requires printing every pixel on the object, so the resolution of each small square is somewhat grainy. Additionally, the color of the object is also limited, with each pixel having only two states: transparent or the color on the dye. That is to say, when the blue dye is activated, it can only change from blue to transparent, while the yellow dye can only display yellow.
However, the repeatable programmable ink designed by the research team for PhotoChromeleon allows you to create any pattern, from various animals to vast landscapes, to colorful flames, etc., offering a wider range of colors to choose from. This is precisely because they have mastered the interaction between each dye and different wavelengths of light, enabling them to control each color channel by activating and deactivating the corresponding light sources. The researchers have also developed a user interface to automatically handle the design and corresponding patterns, which can handle projects according to different needs. Users can load their own blueprints and let the program automatically generate the mapping to be “painted” on the object.
“This special dye can provide rich customization options, thereby improving production efficiency and reducing overall waste,” said Yuhua Jin, a postdoctoral fellow at CSAIL and the first author of the project’s recent paper. “Users can personalize their items and appearance in daily life without having to purchase different colors and styles of the same item multiple times.”
Of course, this research still has some issues that need to be resolved. Although the current photochromic dyes have a wide color gamut, they cannot display all colors. For example, magenta and cyan do not have good matching options. Therefore, the research team still needs to estimate the closest color to fill the gaps. They stated that they plan to expand this research through collaboration with materials scientists to create better dyes. “By giving users the autonomy to personalize their items, countless resources can be retained, and the opportunity to creatively change your favorite items is unlimited,” said Professor Stefanie Mueller of MIT.