Popular Science explains:
...known as supramolecular assembly, these self-healing polymers are composed of small molecules assembled into long, polymer-like chains using metal ions as a kind of “molecular glue” ... under intense ultraviolet light that molecular glue comes undone, allowing the material to flow like a liquid and fill in a scratch or tear. Remove the UV source, and the polymer glue sets again, re-chaining the polymer and creating a solid coating once again.
The self-healing properties of smart polymers are attractive, but I wonder what happens when sunlight hits a car coated with smart polymers. Does the surface go molten until sunset, or is the intensity of ultraviolet light required greater than that emitted from the sun? Maybe that's one of the items yet to be worked out.
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