Fixing the cracks

Cracks in polymers are often invisible, and in applications such as electronic circuits, medical implants, and aircraft parts, they can cause major failures.

Polymers which can repair themselves would be a valuable commodity - and a team led by Jeff Moore of the Beckmann Institute of the University of Illinois has taken an important step towards developing one.

The polymer is an epoxy composite, containing microcapsules of dicyclopentadiene (DCPD) and particles of a ruthenium complex known as Grubb's catalyst. When a crack opens, it travels towards a capsule and ruptures it, spilling liquid DCPD. When this encounters a catalyst particle, it triggers a metathesis polymerisation reaction, which cross-links the DCPD into a sticky material that seals the crack.

The DCPD-Grubb combination is extremely expensive, however, so Moore's team is looking at using similar techniques with different substances. One candidate is the Bergman cyclisation of enediynes, which generates radicals that can initiate polymerisations. Some enediynes undergo this reaction when subjected to tensile stress.

Moore's team is trying to produce this effect at room temperature.