Broken Rubber Bands Fixed Like Magic

There's a popular magic trick where a magician cuts a piece of string in two. Then, after wrapping the strings in complex ways around his fingers, he pulls out a single long piece of string.

While the string trick is a secret only magicians know, scientists have recently developed a similar trick of their own. But instead of string, they use rubber. And instead of magic, they use a science field called "supramolecular chemistry."

The scientists, from the Higher School of Industrial Physics and Chemistry in Paris, have created a new type of rubber, making it out of vegetable oils and urea (the same stuff found in human urine).

They made elastic rubberbands out of the new rubber, and found that, when they cut the rubberband in two, they could immediately press the two cut ends together and reattach them. There's no glue or heat involved, and the rubberband can be cut many times while maintaining its ability to be put back together.

As researcher Ludwik Leibler explains, the ability to repair itself is due to the rubber's small molecules. Normal rubber consists of large molecules, requiring strong covalent bonds to hold them together.

But the small molecules can be held together by weaker hydrogen bonds. When two cut ends of the rubberband are brought together, molecules on each side make bonds with molecules on the other side. The ends have to be brought in contact quickly, though. Otherwise, the molecules will form bonds with other molecules on their own side, and won't be able to bond to the other side.

The researchers hope to develop different types of materials besides rubber that have this self-repairing property. The chemical company Arkema is already working on commercializing the process.

via: New York Times

Lisa Zyga
Science Blogger