Easing the Way for Separation

Summer 2014

Robert Cammarata (left) with Stephen Farias

Carbon nanotubes, tiny pipes made of carbon atoms, have electronic properties that make them suitable for everything from computers and sensors to displays and batteries. Depending on the application, electronics manufacturers need nanotubes that are either semiconducting or metallic. The problem is that the process used to make these tiny tubes yields mixtures containing both kinds. And while a commercial method for separating the nanotubes does exist, the purified tubes it produces are expensive.

But electronics makers may soon be able to pay much less for pure nanotubes in the electronic flavor of their choice. Whiting School materials science and engineering Professor Robert Cammarata and his graduate student Stephen Farias have worked with Jacob L. Hain Professor of Physics Chia-Ling Chien to come up with an efficient, cost-effective way to separate the two types of nanotubes.

Electronics makers may soon be able to pay much less for pure nanotubes in the electronic flavor of their choice.

It should be possible to use the technique for separation at industrial scales, says Farias, who completed his PhD this spring. He speculates that the new technique will cut the cost of producing purified nanotubes to less than a fifth of the current market price.

Today’s commercial separation method relies on sorting tubes based on slight differences in density and chemistry. But the method is labor-, energy- and timeintensive and uses a variety of chemicals. This makes it expensive and less than ideal from an environmental standpoint.

The Whiting School scientists’ technique is much simpler. It involves suspending the nanotubes in water and then exposing them to an electric field of a certain frequency and magnitude under specific conditions. “This results in a physical force acting on the nanotubes,” Cammarata explains. “The force drives the semiconducting and metallic nanotubes in opposite directions because of the large difference in their electronic properties.”

The researchers can then simply scoop out the separated nanotubes. The method should be quick and, because it does not involve special equipment or chemicals, keep cost and environmental impact low.

The technique’s promise has prompted the researchers to file for U.S. patent protection. They have also put together a business plan to launch a startup. Cammarata proudly says that theirs is the first nonbiological technology being refined through the FastForward accelerator, a Johns Hopkins–run incubator established to help turn Johns Hopkins intellectual property into business ventures.

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