The result was a surprise, Ozden said. "Until now, we knew we could use mechanical forces to shorten and cut carbon nanotubes. This is the first time we have showed carbon nanotubes can be unzipped using mechanical forces."
The researchers fired pellets of randomly oriented, multiwalled carbon nanotubes from a light gas gun built by the
"Hypervelocity impact tests are mostly used to simulate the impact of different projectiles on shields, spacecraft and satellites," Ozden said. "We were investigating possible applications for carbon nanotubes in space when we got this result."
The effect was confirmed through molecular simulations. They showed that when multiwalled tubes impact the target, the outer tube flattens, hitting the inside tubes and unzipping them in turn. Single-wall nanotubes do just the opposite; when the tube flattens, the bottom wall hits the inside of the top wall, which unzips from the middle out to the edges.
Ozden explained that the even distribution of stress along the belly-flopping nanotube, which is many times longer than it is wide, breaks carbon bonds in a line nearly simultaneously.
The researchers said 70 to 80 percent of the nanotubes in a pellet unzip to one degree or another.
Ozden said the process eliminates the need to clean chemical residues from nanoribbons produced through current techniques. "One-step, chemical-free, clean and high-quality graphene nanoribbons can be produced using our method. They're potential candidates for next-generation electronic materials," he said.
Co-authors include Pedro Autreto, a postdoctoral researcher at the
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