Researchers from the Swiss Federal Laboratories for Materials Science and Technology (Empa) and ETH Zurich have developed a fiber coating that changes color in response to high temperatures brought on by fire or friction.

Although the coating was developed back in 2018, this is the first time the researchers were able to apply the coating to curved strands. This was accomplished via a sputtering process wherein the microscopic particles of a solid material are ejected from its surface, after the material is inundated with energetic particles of a plasma or gas.

Fiber before and after heat. Source: EMPA

According to the team, three layers were added to the fiber. The first l silver, which serves as a reflector and the second was a layer of titanium nitrogen oxide applied to stabilize the silver. A final 20 nm thick layer of germanium-antimony tellurium is the portion of the coating that changes color when exposed to heat, crystallizing and changing from blue to white.

Applied to objects such as safety rope used by firefighters or on suspension ropes used on construction sites, the coating could reveal that the ropes have been exposed to high temperatures that could potentially and unknowingly compromise the mechanical integrity of the ropes. The color change in the fiber could signal such exposure, potentially averting failure or even catastrophe.