Scientists in Germany have developed a graphene-based coating that changes color when deformed. Based on the natural iridescence in fish skin, it could be used as a warning system for hidden damage in bridges, buildings, and other structures.
Chemistryworld.com reports, “Many materials are coloured by chemical pigments, which absorb light at particular wavelengths and reflect the remaining light, which we see as colour. Other materials, however, are given colour by periodically arranged microscopic surface structures. These cause interference between reflected light waves, amplifying them at specific visible frequencies. This strategy is used in some of nature’s most vibrant materials, from fish scales to peacock feathers, butterfly wings and cephalopod skins.”
“The new material is a kind of traffic light to warn of hidden damage in buildings and vehicles, says Gao, as it changes colour depending on deformation. Normally, the coating is red; however, when deformed, it appears yellow, and when cracked at the micrometre scale, green. This colour-changing ability comes from a careful initial alignment of the graphene flakes in semi-transparent, parallel layers, coating a glass fibre. Under stress, the layers compress and flatten, changing the interference and colour of reflected light.”
The discovery could have huge implications in structures such as dams, which often result in structural failure due to unnoticed small cracks and deformations, such as the Oroville dam in California in February of this year. Coating structures of vehicles in Gao’s material could be a way to give a clear visual warning sign of new damage.
Real-world applications, however, will first require much more knowledge about the properties and behaviour of the coating, notes Gao.