Colour-changing smart material
A new, synthetic material changes colour when it is twisted or stretched. Such a smart material could be used for any number of applications. We take a look.
In nature, many colours are derived from pigments. Some of the most intense, such as those found in opals, feathers and wings, are due to the innate surface structure. Natural opals are formed when water evaporates, leaving behind silica spheres that settle into layers. These spheres reflect light at certain wavelengths, producing the vivid colours. The nacre in pearls works in a similar way.
Scientists from the University of Cambridge teamed up with Germany’s Fraunhofer Institute for Structural Durability and System Reliability to create ‘polymer opals’, a synthetic material that mimics the surface structure of natural opals.
The trick is a coating that uses synthetic, nano-particle spheres with a rubbery outer shell. Like natural opals, the surface structure of these polymer opals reflects light, resulting in a strong, structural colour similar to that of a natural opal.
The precise colour of this synthetic material depends upon the size of its spheres. Because the material has a rubbery consistency, the spacing between the spheres changes when the material is twisted or stretched, and this changes the material’s colour. When stretched, the material appears blue and when compressed, the colour shifts towards the red spectrum. Upon release, the material returns to its original colour.
Because this new material is flexible, colourful and doesn’t fade over time, it may have many useful and fascinating future applications. These polymer opals get their colour from surface structure alone, so they don’t fade or run and could be used as a substitute for the current, toxic dyes in clothing.
Another application for polymer opals could be in the sensing industry. The material’s colour-changing properties could make it useful in mechanical strain sensors for example, as its colour would reveal how much stress an item is experiencing.
Any number of possibilities can be imagined. For now, the researchers are looking for a manufacturing partner to bring these new opal materials to market.