Researchers at Stanford University have devised a method by which they can spray single-walled carbon nanotubes (SWNTs) onto a thin layer of silicone and create a flexible and stretchable pressure sensor.
The researchers, led by Zhenan Bao, associate professor of chemical engineering, published their work in the journal Nature Nanotechnology this week under the title "Skin-like pressure and strain sensors based on transparent elastic films of carbon nanotubes."
"This sensor can register pressure ranging from a firm pinch between your thumb and forefinger to twice the pressure exerted by an elephant standing on one foot," said Darren Lipomi, a postdoctoral researcher in Bao's lab, who is part of the research team, in the Stanford article covering the research.
The researchers discovered that when they sprayed SWNTs onto silicone, the SWNTs naturally formed themselves into clumps, or “nanobundles.” When the silicone was initially stretched, those “nanobundles” aligned themselves in the direction of the stretching. On release, the nanobundles form into “nanosprings,” which in the silicone material act as electrodes.
"After we have done this kind of pre-stretching to the nanotubes, they behave like springs and can be stretched again and again, without any permanent change in shape," Bao is quoted as saying in the article.
The remarkable bit is that after the initial stretching forms the SWNTs into nanosprings, they can undergo numerous stretches without losing their electrical conductivity.
The initial aim of the research was looking not for high sensitivity, but instead to exploit the characteristics of transparency and its flexibility. However, according to Bao, they need only make some changes to the surface of the electrodes to increase its sensitivity.
A video that accompanied the Stanford press release on this story (see below) provides some of the application potential for the use of the material as an artificial skin both for robotics and artificial limbs for amputees.