Nanotube-filled capsules could restore conductivity to damaged electronics

14-Sep-09

Researchers are developing a material that could let a circuit self-repair small but critical damage caused by such an impact. Capsules, filled with conductive nanotubes, that rip open under mechanical stress could be placed on circuit boards in failure-prone areas. When stress causes a crack in the circuit, some of the capsules would also rupture and release nanotubes to bridge the break. The researchers, from the University of Illinois at Urbana-Champaign, are also working on capsule additives designed to heal failures in lithium-ion battery electrodes, to prevent the short-circuiting that can sometimes cause a fire. Previous research into self-healing materials has mostly focused on restoring mechanical properties after a damaging event. The researchers have, for example, already made self-healing coatings that can repair scratches and prevent corrosion on boats or car chassis. Now the group has brought the same techniques to the problem of restoring electronic properties. These failures may become an even bigger problem as flexible electronics, which are subject to much more mechanical stress, become widespread. To make their self-healing material, Braun and Moore encapsulated carbon nanotubes inside polymer spheres about 200 micrometers in diameter each. They selected carbon nanotubes because of their high electrical conductivity and because their elongated shape does a good job of lining up to bridge gaps. In proof-of-concept studies, the researchers ripped the capsules apart and placed the resulting mixture between the tips of two electrical probes. The released nanotubes formed a bridge that completed the circuit between the two probes. Though the polymer itself isn't conductive, this didn't impede the flow of current -- there was a net positive increase in conductivity after the rupture.