Soldiers of the future could use camouflage inspired by chameleons, which could change almost in an instant.
We all sometimes want to blend in with our surroundings, but researchers from the University of Cambridge have taken this to a whole new level. In a paper published to Advanced Optical Materials, they revealed the creation of an artificial ‘chameleon skin’ that can change colour when exposed to light, giving it applications in active camouflage and large-scale dynamic displays.
The material is made up of tiny particles of gold coating in a polymer shell, which are then squeezed into microdroplets of water in oil. When exposed to heat or light, the particles stick together to form different colours.
In the wild, chameleons and cuttlefish change their skin colour using chromatophores – skin cells with contractile fibres that move pigments around. To blend in with their background, these creatures squeeze these skin cells together to make them transparent.
In this new artificial camouflage, the researchers used light-powered nanomachines instead of contractile fibres, with the cells replaced by the microdroplets of water. When heated to temperatures above 32 degrees Celsius, the nanoparticles store large amounts of elastic energy in a fraction of a second, as the polymer coatings expel all the water and collapse.
This process forces the nanoparticles into tight clusters but, when cooled, the polymers take on the water and expand like a spring. What determines the camouflage’s colour is the geometry of the bound nanoparticles.
For example, when the nanoparticles are spread apart it appears red, but appear dark blue when clustered together. However, the droplets of water also compress the particle clusters, causing them to shadow each other and make the clustered state nearly transparent.
Right now, the Cambridge camouflage is limited to just a single layer so is only able to change to one colour. However, different nanoparticle materials and shapes could be used in extra layers to make a fully dynamic material, like real chameleon skin.
The researchers also saw that the artificial cells actually ‘swim’ similar to the algae Volvox. By shining a light on one edge of the droplets, it causes them to peel towards the light and push them forward.
“This work is a big advance in using nanoscale technology to do biomimicry,” said co-author Sean Cormier. “We’re now working to replicate this on roll-to-roll films so that we can make metres of colour changing sheets.”