The team made the coating in an initial red, but when deformed, it appears yellow, and when cracked at the micrometer scale, green. This color-changing ability comes from a careful 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 color of reflected light. In fact, by overlapping graphene nanoplatelets (GNPs) with ordered and disordered features using a special deposition approach, unique “fish scale” like structures are achieved. Variable structural coloration is observed through the mechanical tuning of fine parallel multilayers.
Since structural failure often starts with tiny cracks and deformations which can hard to detect, this coating could give a clear visual warning of nascent damage before it accumulates and becomes a real danger. Real-world applications, however, will first require more knowledge about the properties and behavior of the coating, note the researchers.