A light touch helps heal scratched coatings------Polymer material repaired by UV

Richard Jansen

AN INTERNATIONAL team of researchers has developed a polymer-based material that can rapidly heal itself when placed under ultraviolet light.
The scientists, working in the US and Switzerland, envision their material being used in vehicle paints and furniture varnishes. If your car gets scraped or a cat decides to tests its claws on a favourite bookcase, it should be less than a minute’s work with a lamp to make the problem disappear.
"We can simply use heat to heal these materials," Mark Burnworth, a graduate student at Case Western Reserve University, Ohio, said. "But by using light we have more control because it allows us to target only the defect and leave the rest of the material untouched."
The mechanism that drives this rapid repair is known as supramolecular assembly. It relies on the molecules within the material being considerably smaller than the long, chain-like ones found in conventional polymers. These are assembled into longer chains themselves by metal ions, making a material that behaves like a normal polymer – a “metallo-supramolecular polymer.”
"These polymers have a Napoleon complex: in reality they're pretty small but are designed to behave like they're big by taking advantage of specific weak molecular interactions," said Stuart Rowan, a professor of macromolecular engineering and science and director of the Institute for Advanced Materials at Case Western Reserve University.
When the polymers are irradiated with intense ultraviolet light, the long chains become temporarily unglued and the once-solid material turns into a liquid. Turn the light off and it reassembles, solidifying as its original properties return. One consequence of this process is that a short burst from a lamp can erase shallow scratches, healing any cuts in the polymer.
"Their molecular design allows the materials to change their properties in response to a high dose of ultraviolet light," said Christoph Weder, a professor of polymer chemistry and materials and the director of the Adolphe Merkle Institute in Switzerland.
The polymers are not yet ready for commercial use but, according to Rowan: "One of our next steps is to use the concepts we have shown here to design a coating that would be more applicable in an industrial setting."

From www.tcetoday.com