New Artificial 'Chameleon Skin' Changes Color when Exposed to Light, Heat

The mechanism is not unlike that of chameleons, cuttlefish, or other animal species who use color-change as a defense. These animals use what are known as chromatophores, which are skin cells built with fibers that can contract to shift the pigments in the skin around. When spread out, the colors of the skin is fully-displayed. As it contracts, it can combine with nearby pigments to appear a different color or, if fully contracted, can even make the cell fully transparent.

The new material from the Cambridge researchers achieves a similar effect using the polymer-coated gold fibers, with the droplets of water behaving like the skin cells of a chameleon.

When the researchers raise the temperature of the material above 32 degrees Celsius, the polymer nanoparticles store elastic energy as they collapse, expelling whatever water they retain and clumping together. When cooled, the nanoparticles absorb water instead, spreading themselves apart from the others. This process can happen in a fraction of a second.

“Loading the nanoparticles into the microdroplets allows us to control the shape and size of the clusters, giving us dramatic colour changes,” said Dr. Andrew Salmon, from Cambridge’s Cavendish Laboratory and co-first author of the paper.

The color the nanoparticles appear depends on the geometry they take on when they clump together. When they are spread apart, they appear red, when clumped together, they look more dark blue. The droplets of water can also compress the particles together, causing them to appear transparent as they shadow one another.

So far, the researchers have only been able to produce a single layer of the material, so there can only be one color at a time. But by using several layers and different nanoparticle geometries, different colors could be produced, making the resulting material much more dynamic like the biological mechanisms that inspired it.

The researchers also found that when the material is exposed to different intensities of light, the nanoparticles can be made to 'swim' along a surface, which--if controlled--could change the color of the material by altering the geometry of the nanoparticles.

“This work is a big advance in using nanoscale technology to do biomimicry,” said Sean Cormier, co-author of the paper. “We’re now working to replicate this on roll-to-roll films so that we can make metres of colour changing sheets. Using structured light we also plan to use the light-triggered swimming to ‘herd’ droplets. It will be really exciting to see what collective behaviours are generated.”