Stretchy electronics

Physicists in Japan have found a way to disperse carbon nanotubes into a liquid polymer in order to create a rubbery material that conducts electricity. The inventors say that their material, which is more conductive than other elastic materials, is an important step towards realizing “stretchy” electronics for robotics and other electronic devices.

In the past when researchers have tried to create nanotube–polymer composites, strong intermolecular forces between the nanotubes has always made the structures clump together, producing a weak material. However, by grinding nanotubes with an ionic liquid, the Japanese group — led by Takao Someya from the University of Tokyo — has managed to make them evenly dispersed.

Using this technique, the researchers can swap as much as a fifth of the polymers’s weight for nanotubes without reducing its mechanical flexibility. The resulting material — fused with the electrical conductivity of nanotubes — can be stretched up to 70% without being damaged (Science Express 10.1126/science.1160309).

“This expands the application horizon of carbon nanotubes in an important new direction” says Ray Baughman at the University of Texas. “The most surprising discovery is that the addition of up to 20 %wt nanotubes does not reduce elastic deformability”.

Stretchy electronics

While many engineers focus their efforts on miniaturizing electronic devices, the pursuit of stretchy electronics presents engineers with some altogether different challenges. Desirable materials need to exhibit both excellent electronic performance and physical robustness.

Early attempts to make stretchy electronics have tended to either embed standard electronic components in rubber or to directly integrate them with plastic films. Although Someya recognizes there have been some significant advances, he believes devices have been held back by inelastic wiring.

Someya’s team begin creating their stretchy electronic material by grinding nanotubes with an ionic liquid of 1-butyl-3-methylimidazolium bisimide. They add the resulting thick, black paste or “bucky gel” to a liquid polymer and spread it on a glass plate. Finally, they coat it with silicone rubber and leave it to set.

Currently the team are optimizing the electric and mechanical properties of their elastic conductors. They are also investigating new economical printing processes which could enable the material to replace the fine wires in integrated circuits.

As well as improving existing technologies, Someya hopes the elastic conductors will open the doors to applications that have been closed for conventional silicon-based electronics — for example, electronic artificial skins.