It heals and grows together: Polymer with amazing self-healing properties

Jan 12, 2011

(PhysOrg.com) -- Sooner or later, a cut to the skin or a broken bone will heal on its own; however, a scratch to a car's paint or a tear in the wing of an airplane will not. Materials with self-healing properties could help extend the durability of products and make repairs easier.

Krzysztof Matyjaszewski and his co-workers at Carnegie Mellon University (Pittsburgh, USA) and Kyushu University (Japan) have now developed a polymer that can repair itself when irradiated with -- over and over again. As the scientists report in the journal , this is the first material in which capped covalent bonds repeatedly reattach, even allowing fully separated pieces to be fused back together.

Some previous solid self-healing materials contain tiny capsules that tear open to release a chemical agent when the material is damaged and have been able to repair themselves only one time. Other materials, including some gels, can repair themselves repeatedly but lack the covalent bonds that increase materials strength and stability.

In contrast, the new polymeric material produced by the American and Japanese team is stable and repairs itself again and again. The secret to their success is that the polymer is cross-linked through trithiocarbonate units. These are bonded to three sulfur atoms, two of which use their second bonding position to attach to another carbon atom. These groups have a special property: they can restructure under UV light. The light breaks one carbon–sulfur bond in the trithiocarbonate groups. This produces two radicals -- molecules with a free, unpaired electron. The radicals are very reactive and attack other trithiocarbonate groups to form new carbon–sulfur bonds while breaking others to form more free radicals. The chain reaction stops when two radicals react with each other.

The researchers were able to heal cut polymer fragments with irradiation—either immersed in liquid or in bulk. They only had to firmly press the cut edges together and irradiate them. The edges grew back together by means of the radical re-organization process described above.

The self-healing effect goes much further: even shredded samples could simply be pressed together and irradiated to be fused into a continuous piece. The resulting object was in the shape of the cylindrical tube in which the procedure was carried out. This self-healing process can be carried out repeatedly on the same sample. The material is thus also interesting as a new recyclable product.

Explore further: Chiral breathing: Electrically controlled polymer changes its optical properties

More information: Krzysztof Matyjaszewski, Repeatable Photoinduced Self-Healing of Covalently Cross-Linked Polymers through Reshuffling of Trithiocarbonate Units,
Angewandte Chemie International Edition, dx.doi.org/10.1002/anie.201003888

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User comments : 3

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Moebius
not rated yet Jan 13, 2011
A scratch is not a tear. Scratches in car paint remove material. Don't expect self-healing scratches on car paint except maybe extremely fine ones that are almost invisible to begin with. A car scratch might be able to be fixed with the application of more of the polymer on a cloth though. As long as it isn't a deep scratch and is only in the clear coat.
Donutz
1 / 5 (2) Jan 13, 2011
a scratch's edges may be far apart in the middle, but they're pretty close together at the ends. Think of a zipping-up motion. Assumes the stuff has enough stretch and flexibility to do that, of course.

I just hope this stuff ONLY reattaches to itself. Otherwise, I detect a nightmare brewing...
Sanescience
1 / 5 (1) Jan 13, 2011
Ah yes, materials that do not degrade in the environment... what could possibly go wrong?!

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