Colour-changing artificial ‘chameleon skin’ powered by nanomachines


28-08-2019
chameleon

Researchers have developed artificial ‘chameleon skin’ that changes colour when exposed to light and could be used in applications such as active camouflage and large-scale dynamic displays.

The material, developed by researchers from the University of Cambridge, is made of tiny particles of gold coated in a polymer shell, and then squeezed into microdroplets of water in oil. When exposed to heat or light, the particles stick together, changing the colour of the material. The results are reported in the journal Advanced Optical Materials.

In nature, animals such as chameleons and cuttlefish are able to change colour thanks to chromatophores: skin cells with contractile fibres that move pigments around. The pigments are spread out to show their colour, or squeezed together to make the cell clear.

The artificial chromatophores developed by the Cambridge researchers are built on the same principle, but instead of contractile fibres, their colour-changing abilities rely on light-powered nano-mechanisms, and the ‘cells’ are microscopic drops of water.

When the material is heated above 32C, 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 has the effect of forcing the nanoparticles to bind together into tight clusters. When the material is cooled, the polymers take on water and expand, and the gold nanoparticles are strongly and quickly pushed apart, like a spring.

“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, the study’s co-first author.

The geometry of the nanoparticles when they bind into clusters determines which colour they appear as: when the nanoparticles are spread apart they are red and when they cluster together they are dark blue. However, the droplets of water also compress the particle clusters, causing them to shadow each other and make the clustered state nearly transparent.

At the moment, the material developed by the Cambridge researchers is in a single layer, so is only able to change to a single colour. However, different nanoparticle materials and shapes could be used in extra layers to make a fully dynamic material, like real chameleon skin.

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Reproduced courtesy of the University of Cambridge

 

The University of Cambridge is acknowledged as one of the world's leading higher education and research institutions. The University was instrumental in the formation of the Cambridge Network and its Vice- Chancellor, Professor Stephen Toope, is also the President of the Cambridge Network.

University of Cambridge (cam.ac.uk)