Laser-fueled vortex creates nanotube forest

The nanotubes aligned (left) and returning to their random orientation after the electric field and laser were turned off (right)(Credit: Purdue University/Avanish Mishra/Steven Wereley)

While small in size, carbon nanotubes can be mighty in their applications. Among many other things, the tiny cylinders of carbon have helped researchers figure out how to make metals more resistant to radiation, detect decaying meat, destroy cancer cells, and create fibers for artificial muscles. But manipulating carbon nanotubes can be tricky, considering that their diameter is about 50,000 times smaller than a human hair. Researchers at Purdue University have just come up with a way to get carbon nanotubes to get in line – literally – by using electrical pulses and a vortex created by laser light.

The method they used to manipulate the tubes consists of two stages. In the first, a technique called rapid electrokinetic patterning causes the nanotubes to orient vertically. This process consists of two electrodes, each made from a transparent conductive material called indium tin oxide, with nanotubes suspended in deionized water between them. When an electrical field is applied to the setup, the nanotubes all stand on end inside the water. By applying different current strengths to the liquids, the researchers were able to tune how many tubes were affected.

Next, an infrared laser is applied to the water, which heats it up and creates a donut-shaped swirling vortex. The vortex essentially traps the nanotubes and allows them to be moved and positioned anywhere on the surface of the indium tin oxide. Such precise positioning could have applications for positioning nanotubes in sensors, circuits or microchips.

"When we apply the electric field, they are immediately oriented vertically, and then when we apply the laser, it starts a vortex, that sweeps them into little nanotube forests," says Steven T. Wereley, a professor of mechanical engineering at Purdue University.

While the walls of carbon nanotubes can be as thin as a single atom, in this particular study, multi-walled versions were used. The researchers believe that the manipulation technique can also be applied to other micro structures such as nanorods and nanowires, such as those recently used to create a battery with a massive capacity to be charged and recharged. They've received a US patent on the system and their work was published last month in the journal Microsystems and Nanoengineering.






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