'Sticky nanotubes' hold key to future technologies

This composite image taken with an electron microscope shows a side and bottom image of a nanotube attached to a "microcantilever, " a component in atomic force microscopes. Researchers at Purdue... Click here for more information.

WEST LAFAYETTE, Ind. - Researchers at Purdue University are the first to precisely measure the forces required to peel tiny nanotubes off of other materials, opening up the possibility of creating standards for nano-manufacturing and harnessing a gecko's ability to walk up walls.

So-called "peel tests" are used extensively in manufacturing. Knowing how much force is needed to pull a material off of another material is essential for manufacturing, but no tests exist for nanoscale structures, said Arvind Raman, an associate professor of mechanical engineering at Purdue.

Researchers are trying to learn about the physics behind the "stiction," or how the tiny structures stick to other materials, to manufacture everything from nanoelectronics to composite materials, "nanotweezers" to medical devices using nanotubes, nanowires and biopolymers such as DNA and proteins, he said.

Flexible carbon nanotubes stick to surfaces differently than larger structures because of attractive forces between individual atoms called van der Waals forces.

"Operating in a nanoscale environment is sort of like having flypaper everywhere because of the attraction of van der Waals forces," Raman said. "These forces are very relevant on this size scale because a nanometer is about 10 atoms wide."

Mechanical engineering doctoral student Mark Strus made the first peeling-force measurements for nanotubes in research based at the Birck Nanotechnology Center in Purdue's Discovery Park.

Findings were detailed in a research paper published in February in the journal Nano Letters. The paper was written by Strus; materials engineering doctoral student Luis Zalamea; Raman; Byron Pipes, the John Leighton Bray Distinguished Professor of Engineering; NASA engineer Cattien Nguyen; and Eric Stach, an associate professor of materials engineering.

The energy it takes to peel a nanotube from a surface was measured in "nanonewtons," perhaps a billion times less energy than that required to lift a cup of coffee. That peeling energy is proportional to the nanotube's "interfacial energy," which is one measure of how sticky something is, Strus said.