When trying to invent an adhesive, Yu Yanagisawa at the University of Tokyo discovered a polymer glass that is not only strong, but can be compressed back together when shattered under manual compression for just 30 seconds. His work was published in the journal Science and picked up by news sources across the country as a potential solution to reduce e-waste. The material is currently under development at the university and could potentially be used in smartphones so that people will not have to replace broken screens.
The material, polyether-thioureas, is a clear polymer that is electrically conductive, making it a viable material for touchscreens. Rather than using additives that make it self-adhesive when shattered, the material contains hydrogen bonds that allow it to heal more than just 2 or 3 times at room temperature. In addition, these hydrogen bonds make the material very strong. This is a breakthrough because strength tends to be a tradeoff for self-healing polymers.
“High mechanical robustness and healing ability tend to be mutually exclusive,” the researchers write. Most hard plastics are made up of long, entangled polymer chains, so it takes very high melting temperatures as high as 120 °C to untangle their polymer chains, and then controlled cooling conditions to reform their crosslinks and re-solidify them into solid polymers.
The material achieves its high strength and self-healing capabilities through a natural zig-zag hydrogen-bonded array. When the material is broken under high strain or stress, an added structural component facilitates the exchange of hydrogen-bonded pairs between polymers under compression so it can easily heal.