In a scientific breakthrough, a team of researchers headed by an Indian American professor has developed a new process to make "nano-skins" that would conduct electricity for applications like electronic displays, electronic papers and sensors.
The "nano-skin" polymer was created by researchers at Rensselaer Polytechnic Institute in New York, headed by Pulickel Ajayan, the Henry Burlage Professor of Materials Science and Engineering.
Swastik Kar, the lead author, said the new material may well be used to build highly efficient electronic parts for highly flexible electronic displays and might have many other applications "all the way from adhesive structures and velcro-like materials to nanotube interconnects for electronics".
Carbon nanotubes, made of rolled-up sheets of tightly-bound carbon molecules, are incredibly strong and excellent conductors. But the tubes, which can have a diameter of just a nanometre, are also inflexible and easily damaged.
Nanotube arrays typically don't maintain their shape when transferred because they are held together by weak forces.
But the team has developed a new procedure that allows them to grow an array of nanotubes on a separate platform and then fill the array with a soft polymer.
When the polymer hardens, it is essentially peeled back from the platform, leaving a flexible skin with organised arrays of nanotubes embedded throughout.
The skins can be bent, flexed, and rolled up like a scroll, all while maintaining their ability to conduct electricity, which makes them ideal materials for electronic paper and other flexible electronics, according to Ajayan.
The RPI team created a more malleable nanotube "skin" by using larger multi-walled carbon nanotubes, with a diameter of about 10 nanometres.
The nanotubes were deposited by chemical vapour deposition on to a silicon dioxide layer, which left the tubes pointing vertically up from the surface.
The scientists then poured liquid polydimethylsiloxane polymer over the substrate. The liquid covered and filled the carbon nanotubes, before hardening.
Finally, the flexible polymer, infused with carbon nanotubes, was peeled away from the substrate.
The researchers had also lithographically etched a spotted pattern into the silicon dioxide to show that specific arrangements of nanotubes are possible.
Nanotubes do not form on the underlying silicon. "Researchers have long been interested in making composites of nanotubes and polymers, but it can be difficult to engineer the interfaces between the two materials," said Ajayan.
The research is published in the March 2006 edition of the journal Nano Letters. "We have found a way to get arrays of nanotubes into a soft polymer matrix without disturbing the shape, size, or alignment of the nanotubes," said Ajayan.
The team recently reported a process for creating artificial 'gecko feet' with 200 times the sticking power of the real thing, using nanotubes to imitate the thousands of microscopic hairs on a gecko's footpad.
The researchers also envision using the process to build miniature pressure sensors and gas detectors. The team has shown that flexible materials demonstrate an extremely useful physical property called field emission.
When a voltage is applied to certain materials, electrons are pulled out from the surface, which can be used to produce high-resolution electronic displays.
"Nanotubes are very good field emitters because they have a low threshold for emission and they produce high currents," Kar said.
"But when you lay nanotubes very close to each other, each tube tends to shield its neighbor from the electric field," Kar added.
This effect has limited the development of field emission devices based on densely packed, aligned nanotubes, but it seems to go away when the nanotubes are embedded in a polymer, according to Kar.