Colour-changing artificial 'chameleon skin' developed

Cambridge researchers have developed artificial 'chameleon skin' that changes colour when exposed to light and could be used in active camoufl and large-scale dynamic displays.

material is made of tiny particles of gold-coated in a polymer shell and n squeezed into microdroplets of water in oil. When exposed to heat or light, particles stick toger, changing colour of material, according to research published in 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. pigments are spread out to show ir colour or squeezed toger to make cell clear.

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artificial chromatophores developed by researchers from University of Cambridge in UK are built on same principle. However, instead of contractile fibres, ir colour-changing abilities rely on light-powered na-mechanisms, and 'cells' are microscopic drops of water. When material is heated above 32 degrees Celsius, naparticles store large amounts of elastic energy in a fraction of a second, as polymer coatings expel all water and collapse.

This has effect of forcing naparticles to bind toger into tight clusters. When material is cooled, polymers take on water and expand, and gold naparticles are strongly and quickly pushed apart, like a spring.

"Loading naparticles into microdroplets allows us to control shape and size of clusters, giving us dramatic colour changes," said Andrew Salmon from Cambridge.

geometry of naparticles when y bind into clusters determines which colour y appear as: when naparticles are spread apart y are red and when y cluster toger y are dark blue. However, droplets of water also compress particle clusters, causing m to shadow each or and make clustered state nearly transparent.

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At moment, material is in a single layer, so is only able to change to a single colour, researchers said. However, different naparticle materials and shapes could be used in extra layers to make a fully dynamic material, like real chameleon skin, y said. researchers also observed that artificial cells can 'swim' in simple ways, similar to algae Volvox.

Shining a light on one edge of droplets causes surface to peel towards light, pushing it forward. Under stronger illumination, high pressure bubbles briefly form to push droplets along a surface