Scratches that Self-heal in the Sun

A new surface material could heal it's own scratches simply by being left in the sun! Professor Marek Urban explains the clever chemistry behind self-healing.....
15 March 2009

Interview with 

Professor Marek Urban, University of Southern Mississippi


A heap of Pandalus borealis shrimp.


Chris - The work of Professor Marek Urban, who's a researcher at The University of Southern Mississippi. This material has the capacity to repair itself whenever it gets scratched. Sounds ideal for my car whenever I take a trip to the supermarket. Hello Marek, Thank you for joining us on the Naked Scientists. Tell us how this material works.

Marek - Essentially you can create a scratch on simply plastic. It's exposed to sunlight and certain reactive molecules open up. Consequently they react with other species that are present in the system and form what we call crosslinks. Those crosslinks essentially seal the scratches that are mechanically created. It's a little silent species sitting inside of a system that is capable of self-repairing on exposure to ultraviolet light.

A heap of Pandalus borealis shrimp.Chris - Tell us what the actual chemicals are that you've used in the mixture. How different are they from what we're currently using in paints and other surfaces?

Marek - Mostly automotive paints and not only automotive but also floor coatings utilise polyurethanes which are fairly durable and fairly high-performance materials. However, they are not exempt from mechanical damage. What we've created is essentially we took a polyurethane network. Also we incorporated small amounts of chitosan. Chitosan is a derivative of chitin which is the second largest carbohydrate present on Earth after cellulose. This was modified with so-called oxitane and that oxitane ring is one of those reactive types that opens up as you make a mechanical scratch.

Chris - Chitosan is actually a derivative of chitin, as you say. That's the exoskeleton of things like crabs and lobsters, isn't it?

Marek - Exactly. You have plenty of those things, lenses along the coast of the country that deals with fishery. As a matter of fact a portion of our research was funded by the Mississippi Division of Marine Resources. That chitosan was modified with oxitane and that oxitane is a relatively easy-to-open ring. As a mechanical scratch is created that oxitane opens up creating a reactive species. Then, on exposure to UV light, creates another reactive species from chitosan. Those things react again to form a crosslinked network, therefore eliminating scratches.

Chris - To put it simply you have the chitosan which is this molecule and you've coupled onto the side of it a ring structure which , when the paint surface gets damaged, that ring busts open. This makes it chemically reactive and it can then grab either side of the damaged area and link it back together.

Marek - Right. Exactly. The quantities of this material are relatively small. Again, this is a proof of concept, at this stage. We don't seem to see reasons why that shouldn't work in many other systems.

Chris - And just to finish off, when can we see this being used? Is there any reason why we can't expect to see this cropping up on car paints and car surfaces very soon?

Marek - I think we should. There are different types of polyurethanes being used in a variety of systems. Some of them are water-based, some of them are solvent-based. It's sometimes system-dependent but those things can be worked out. I really hope that consumer-driven markets like automotive markets and others, for that matter, will pick up on that and take this seriously.


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