Spin out produces chameleon-like material

A Cambridge University spin out has created a way to produce a colour changing material on an industrial scale.

Researchers at Phomera have created a new way to arrange microscopic spheres into regular layers, which cause materials to change colours when either stretched or twisted. Known as polymer opals, these spheres can be produced using a method called Bend-Induced-Oscillatory-Shearing, allowing hundreds of metres worth of material to be produced.

Professor Jeremy Baumberg, the senior author involved in the research, said: “Finding a way to coax objects a billionth of a metre across into perfect formation over kilometre scales is a miracle. But spheres are only the first step, as it should be applicable to more complex architectures on tiny scales.”

The polymer opals — transparent plastic nano-spheres — are grown in vats. Solid in the middle but sticky on the outside, the spheres are then dried into a solid mass. When sheets containing a sandwich of these spheres are bent around rollers the spheres are forced to form perfectly arranged stacks. The internal structure of these polymer opals was determined using a wide range of techniques including electron microscopy, x-ray scattering and rheology.

By altering the sizes of the nano-spheres, different wavelengths of light are reflected and when the material is twisted and stretched, the distance between the spheres changes, causing colour changes. When stretched the material shifts to the blue range of the spectrum and when compressed, to the red spectrum, returning to its original colour when left to return back to its starting shape.

Uses for this technology include colour changing wallpapers, banknote security or being used to build coatings to reflect away infrared thermal radiation. The results of this experiment were published in Nature Communications.