It has been known for some time that stretchability properties in materials will significantly expand the scope of applications in the electronics industry particularly for large-area electronic displays, sensors and actuators, and unlike conventional devices stretchable electronics can cover arbitrary surfaces and movable parts, opening up a wealth of opportunities. A significant hurdle however has always been in the manufacture of large-area highly stretchable electrical wirings with high conductivity.
That is until a group of scientists from various institutions in Japan developed a synthetic route to producing printable elastic conductors comprising single-walled carbon nanotubes (SWNTs) uniformly dispersed in a fluorinated rubber. [Sekitani et al., nmat (2009), doi: 10.1038/NMAT2459].
Using an ionic liquid and jet-milling, we produce long and fine SWNT bundles that can form well-developed conducting networks in the rubber. Conductivity of more than 100 S cm-1 and stretchability of more than 100% are obtained. Making full use of this extraordinary conductivity, the scientists constructed a rubber-like stretchable active-matrix display comprising integrated printed elastic conductors, organic transistors and organic light-emitting diodes. The display was able to be stretched by 30–50% and spread over a hemisphere without any mechanical or electrical damage.
Sekitani et al developed the printable elastic conductor comprising SWNTs uniformly dispersed in a highly elastic fluorinated copolymer rubber by using an imidazolium ion-based ionic liquid and a jet-milling process. Taking advantage of a process that can uniformly disperse finer bundles of SWNTs in a rubber matrix without shortening the length of the nanotubes, the SWNT rubber composite gel become increasingly viscous, and consequently this material can be finely patterned using direct printing technologies. A printed elastic conductor requires no extra coating and mechanical process, and can stretch by 118% and has an extraordinarily high conductivity of 102 S cm-1.
Sekitani et al integrated such printed elastic conductors with organic transistors and organic light-emitting diodes (LEDs) to realize a truly rubber-like active-matrix organic LED display.
The stretchable materials and integration technology used by Sekitani et al can also be used to create other types of functional electronics such as a rubber-like electrical artificial skin with an integrated, stretchable active matrix and pressure sensors or a rubber-like mechanical actuation system with an integrated, stretchable active matrix and actuators that can create the sensation of touch electrically. The combination of stretchable sensors, actuators and displays can be used to create real, tangible displays and user-friendly human machine interfaces on all kinds of surface.