Safety ropes used by fire brigades or suspension ropes for heavy loads on construction sites can lose their mechanical properties undetected when exposed to high temperatures, friction or fire.
A research team from the Swiss Federal Laboratories for Materials Science and Technology, Empa, Dübendorf/Switzerland, and the ETH Zurich, Switzerland, have now developed a coating that changes color due to their physical reaction to heat thus clearly indicating whether a rope will continue to provide the safety it promises in the future.
3 layers are required to ensure that the fiber actually changes color when heated. The researchers applied silver to the fiber itself, in this case polyester and Vectran (high-tech fiber spun from a liquid-crystal polymer). This serves as a reflector - in other words, as a metallic base layer.
This is followed by an intermediate layer of titanium nitrogen oxide, which ensures that the silver remains stable. Finally, there follows the amorphous Germanium-antimony tellurium (GST) layer, which is just 20 nm thick, that causes the color change. When this layer is exposed to elevated temperatures, it crystallizes, changing the color from blue to white. Depending on the chemical composition of the temperature-sensitive layer, this color change can be adjusted to a temperature range between 100 and 400 °C and thus adapted to the mechanical properties of the fiber type.