Nanoskin makes a flexible friend

A team of researchers has developed a new process to make flexible, conducting “nanoskins” for a variety of applications, from electronic paper to sensors for detecting chemical and biological agents. The materials combine the strength and conductivity of carbon nanotubes with the flexibility of traditional polymers.

Engineering the interface between the two materials for nanotube/polymer composites has proved difficult in the past. The new research has produced a way to get arrays of nanotubes into a soft polymer matrix without disturbing the shape, size, or alignment of the nanotubes.

Nanotube arrays typically don’t maintain their shape when transferred because they are held together by weak forces. But the team’s new procedure 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 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.

”The general concept - growing nanotubes on a stiff platform in various arrays and then transferring them to a flexible platform without losing this organisation - could have many other applications, all the way from adhesive structures and Velcro-like materials to nanotube interconnects for electronics,” said Swastik Kar, a postdoctoral researcher in materials science and engineering at Rensselaer Polytechnic Institute.

The team has shown that the flexible materials demonstrate a 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 neighbour from the electric field.”

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. Tests showed that the team’s nanoskins are excellent field emitters when compared to some of the best values obtained by other research groups.