Military vehicles that change color to be dark at night, and camo-green in the daylight ... could such a thing be possible? Well, it's certainly closer to reality, thanks to research being conducted at the University of Michigan. Scientists there have created a solution that changes color when exposed to light, then changes back when the light is removed. If incorporated into a thin film coating, the result could be chameleon-like surfaces.
The solution consists of negatively- or positively-charged latex paint microparticles suspended in a kerosene-like fluid, pooled on an indium tin oxide substrate.
When light is shone onto a section of that pool, it causes a localized chemical reaction to take place between the fluid and the substrate, creating a current of ions in the fluid. This in turn causes the negatively-charged microparticles to draw together in that area and form crystals, which reflect the light in a given color. The color is determined by the spacing between the particles within the crystals, and that spacing is determined by the wavelength of the light that is being shone on the liquid.
Once the light is turned off, the crystals dissolve, and the liquid returns to its previous color. The process can be repeated indefinitely. If the microparticles are positively charged, incidentally, they will move away from the illuminated area, which still results in a localized color change.
Along with its possible use for camouflaging vehicles, it is hoped that once developed, a film incorporating the technology could also be used for applications such as e-readers and dynamic billboards.
A paper on the research was published today in the journal Nature Communications. In the videos below, you can see the liquid displaying the University of Michigan's M logo as it's exposed to ultraviolet light in the shape of the letter – in the first clip, the logo is formed as negatively-charged microparticles form into crystals, while in the second, the M is created when positively-charged particles retreat from the light.
Source: University of Michigan