Someya first combines carbon nanotubes with an ionic liquid–a liquid containing charged molecules–and a liquid polymer to make a nanotube-rubber paste. Then comes the crucial part: a high-pressure jet that spreads the nanotubes in the rubber.
The jet makes the nanotube bundles thinner without shortening them and disperses the bundles uniformly in the polymer. “The longer and finer bundles of nanotubes can form well-developed conducting networks in rubbers, thus significantly improved conductivity and stretchability,” Someya says. The jet process also increases the material’s viscosity, making it suitable for high-definition screen printing.
The researchers use a printing mask to deposit 100-micrometer-wide lines of the conductor on a piece of rubber. Then they use the lines as a wire grid to connect organic transistors and OLEDs–a transistor addresses each OLED pixel–to make a display that can stretch by up to 50 percent of its original shape. “This work is very impressive,” Rogers says. “The data shows that they can stretch and deform these displays without changing the property of the pixels too much.”
Many other applications could be possible with the stretchable wiring. The researchers could use it to make sensitive artificial skin for robots or prosthetic limbs. Instead of using OLEDs, they would use pressure sensors on the printed conductor. The electrodes could also be used in implantable medical devices to study or repair body organs.
Someya says that Tokyo-based Dai Nippon Printing is interested in commercializing the stretchable display, and a product should be possible in five years. But first, the researchers need to make higher-resolution displays by printing conductor lines narrower than 100 micrometers.