Conductive elastic polymers

Silicon, silicon dioxide, and other materials typically used to make electronic components are intrinsically rigid and brittle, problematic properties if you want to make a compact device that’s tough or flexible. In principle, you could make such devices from stretchy organic materials. The trouble is that suitable insulators and semiconductors exist, but not conductors. The University of Tokyo’s Takao Someya and colleagues have now solved the conductor problem by embedding single-wall carbon nanotubes in a flexible polymer. Prior efforts to dope a polymer with nanotubes had produced composites that were unstretchable due to the tubes’ natural tendency to clump because of attractive van der Waals interactions. Someya’s team mixed ultralong nanotubes with an ionic liquid that disperses them uniformly in the polymer without sacrificing the composite’s flexibility. The result was an elastic compound with a conductivity of 57 siemens per centimeter, two orders of magnitude higher than the most conductive elastomers. As proof of principle that the material is suitable for skinlike circuitry, the group fashioned the compound into thin fishnet-like strips, stretchable up to 134%. Those strips were then used to link an array of semirigid thin-film transistors in the two-dimensional elastic matrix shown here. The black polymer strips are visible through a layer of white silicone rubber added for stability, and the device can be stretched up to 70% with negligible effect on its electrical behavior. (T. Sekitani et al., Science 321, 1468, 2008 .) — R. Mark Wilson