Talk about bouncing back from adversity. A new stretchy material can be cut and rejoined at the same spot just by pressing the broken ends together for a few minutes. The self-healing rubber stays stretchy even after being severed five or six times, or cut and left on the countertop overnight, French researchers say. A chemical manufacturer is already working to create large batches of the material for still hypothetical applications such as sealants and self-healing rubber duckies.
The material's secret is its molecular structure, which resembles a plate of spaghetti, says physicist Ludwik Leibler of the National Center for Scientific Research (CNRS) in Paris, who led the research team. The strands straighten out when pulled, but they relax back to their tangled shape when the tension is released. The result is a rubber that can stretch to six times its resting length, the group reports in the journal Nature.
The self-mending occurs because each strand consists of numerous small molecules of vegetable fat linked to each other and to far-flung neighbors via relatively weak hydrogen bonds, the same chemical bonds that give water molecules their cohesiveness. When the material was cut or ripped, the severed bonds remained chemically sticky for each other.
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Leibler recalls the first time his group ripped the material and pressed the torn ends together gingerly. "It was unbelievable, because after few seconds you could take the sample and the pieces would not fall apart," he says. "And it worked again and again and again." They called the sample "Miracle 1."
A full repair required up to six hours of bonding, the researchers report. They note that a ripped sample could be left overnight before being repaired, although it would not stretch as far, because some of the severed bonds had linked to their neighbors. Recycling a sample into a new shape is easy, Leibler adds—just heat it so the bonds break and reform.
The demonstration does have "a touch of magic about it," biochemists Justin Mynar and Takuzo Aida wrote in an editorial accompanying the paper. Prior self-healing materials relied on embedded capsules of sealant that opened during a break and then had to be replenished, or polymers that required high heat to rebond, they note.
Leibler says the Philadelphia-based chemical maker Arkema, Inc., is working on scaling up the synthesis process, "so that people can play with and dream about it." Among his own dreams are self-healing toys, pipe seals and pavement as well as plastic medical pouches that can be punctured and reused.
