Nobody likes scratches in their car's finish. That's part of the reason why over the years, a number of research facilities have tried to develop self-healing paint. These efforts have resulted in products containing things such as microcapsules that burst open when scratched, elastic resins, and even a chemical derived from the exoskeletons of crustaceans. Now, scientists from the U.S. and Switzerland have developed polymers – which could be used in paint – that heal their own scratches when exposed to ultraviolet light.
The metallo-supramolecular polymers were created by a team from Cleveland's Case Western Reserve University, the Adolphe Merkle Institute at Switzerland's University of Fribourg, and the U.S. Army Research Laboratory.
Made using a process known as supramolecular assembly, the polymers are composed of relatively small molecules assembled into long chains, held together with metal ions. When exposed to intense UV light, those molecules become temporarily "unglued," transforming the material from a solid to a liquid that fills any scratches within less than one minute. Once the light source is removed, the molecules reassemble and the polymers resolidify, sans scratches. The unique properties of the metal ions are said to be the key to the reaction.
In lab tests on polymer samples, the scientists found that they could treat scratches in specific areas by using a highly-focusable lamp like those used by dentists to cure fillings. Simple heat also worked, although it wasn't as easy to control as the UV light. It was also found that the exact same area could be scratched and healed over and over again, which has not been the case with some other self-healing substances.
The researchers say that there is still work to be done before the polymers could be a commercially-viable product – for one thing, it's been discovered that while polymers with the most ordered molecular structures offer the best mechanical qualities, those with the least-ordered structures are the best at healing. Once the bugs are worked out, however, the polymers could eventually find use not only in paint, but also in floor and furniture varnish, and on windows in abrasive environments.