LOS ANGELES, Feb. 28 (UPI) -- University of California researchers say a new, transparent organic plastic can heal itself when cracked, mending fractures repeatedly under simple heating and cooling conditions.
Scientists hope to use the material to self-repair lenses, for sturdier electronics and in construction material.
"It's easy to make, but we hope it can be made even easier," said researcher Fred Wudl, a chemist at the Exotic Materials Institute of the University of California in Los Angeles.
Researchers have tried to make self-repairing materials for decades. Recently they made several breakthroughs with novel substances filled with healing catalysts in little capsules that repaired the material when cracked. However, these solids may not be able to heal repeatedly, and the catalysts are not necessarily stable in the long term.
The UCLA researchers created a new transparent yellow plastic that apparently can heal indefinitely with just mild heat. The new solid is tough at room temperature, with mechanical properties equal to those of commercial, state-of-the-art epoxy resins.
The plastic is made of organic molecular chains or polymers linked together to form a thick mesh. Substances made of these dense weaves often are highly resistant to fracture and solvents, but until now also often proved irreversibly damaged by the high stresses that cause fractures.
Materials chemist James Moore of Rensselaer Polytechnic Institute in Troy, N.Y., called the work "a really neat idea, and it's done in a very elegant way."
"It takes advantage of fundamental chemical principles and combines them in a way that, when you look at it, it seems kind of obvious, but nobody else thought of it that way until now," he told UPI.
"Normally when you break something, if it's a piece of metal or piece of silicon, you end up with a bunch of dangling bonds at the interface and they immediately react with oxygen or whatever else is in the air," Wudl said. "And that's it, you're finished, you can't re-mend it no matter how hot you heat it, unless you really melt it, in which case you have completely disorganized the entire material."
The links that make up the new material mend when heated to 248 degrees Fahrenheit and then cooled back to room temperature.
"The difference here is that once you break it, you don't form dangling bonds. You form two components which when brought close to each other again will react and form the same kind of bond that they had before," Wudl told UPI.
This simple healing process leads to strong molecular bonds and does not require the addition of catalysts or special surface treatments -- all you need to do is heat cracks up for about two hours and let the substance cool. However, Wudl added, once broken, the re-mended plastic is only 60 percent as strong as before because of air trapped during the repair process.
The researchers are working to make the plastic stronger at higher temperatures and to get the yellow color out of it. In addition to self-repairing lenses and building material, Wudl said the plastic could help make electronics more reliable.
"In electronics, the equipment goes through heating and cooling cycles a lot when you turn it on or off," Wudl explained. "Cracks develop, you get debonding, and eventually failure of whatever the component is. If our material were used, it'd re-mend itself."
(Reported by Charles Choi in New York.)