U Kentucky Indian Researchers Create Exotic Form Of Carbon
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12 November 2005 -- Two Indian research students - Mainak Majumder and Nitin Chopra - at the University of Kentucky might be moving closer to creating materials out of exotic forms of carbon that could protect soldiers against deadly chemicals, or allow more efficient nicotine patches to help smokers quit.
In their study, Nanoscale hydrodynamics: Enhanced flow in carbon nanotubes, published November 3rd in Nature, Mainak Majumder, Nitin Chopra and their advisor Professor Bruce J. Hinds of UK's Chemical and Materials Engineering Department, and Rodney Andrews of UK's Center for Applied Energy Research found the flow dynamics of carbon nanotube (CNT) membranes with pores measuring 7 nanometers in diameter permit a fluid flow exceeded the flows predicted by conventional hydrodynamic predictions.

The researchers predict that “these advantages also make the aligned carbon-nanotube membrane a promising mimic of protein channels for transdermal drug delivery and selective chemical sensing.”

Mainak Majumder is a Ph.D. student on leave from India's prestigious Central Glass and Ceramic Research Institute (CSIR) specializing in membrane separations. Ph.D. student Nitin Chopra earned his degree from Indian Institute of Technology, Kanpur (IITK) in Materials and Metallurgical Engineering (2001) with a minor in Environmental Engineering. His current research focuses on applications and selective growth of Nanostructures.

In their study "Enhanced Flow in Carbon Nanotubes," published this week in Nature, the researchers note an "aligned CNT membrane has fast transit approaching the extraordinary speed of biological channels. The membrane fabrication is scalable to large areas, allowing for industrially useful chemical separations.

"(E)ach side of the membrane can be independently functionalized. These advantages make the aligned CNT membrane a promising large-area platform to mimic protein channels for sophisticated chemical separations, trans-dermal drug delivery and selective chemical sensing," the researchers say.

The finding adds weight to the idea that nanotube membranes possibly could be used to form fast, highly efficient filters for all manner of uses. It might be possible, for example, to fashion military uniforms that could "breathe," but also filter out chemical agents like nerve gas, says chemist Bruce Hinds.

They team has been working for several years with nanotubes. The group reported two years ago that it had learned how to combine billions of the tubes to form membranes that could serve as highly efficient filters.

Now, they have found that fluids can pass through those nanotube membranes at very high rates of speed. The rapid-flow effect had been theorized, but the group is the first to confirm it, Hinds said. "Theorists predicted it in about 2001, but finding it was a bit unexpected," Hinds said. "So, it's pretty exciting." According to Hinds, liquids can zip through the membranes because the arrangement of carbon atoms in nanotubes provides an "atomically flat" surface that is "nearly friction free."

The effect, he said, suggests that nanotube membranes could be used to make highly efficient filters that could be tuned to let some materials pass through, while keeping others out. It also could be possible to electrically open or close the tubes, letting materials pass only when desired.

Hinds said, for example, that the researchers already have made highly efficient nicotine patches that use nanotube membranes to quickly and efficiently regulate nicotine flow. (The patches have yet to be tested on humans.) In the future, Hinds said, the technology could lead to inexpensive, but highly efficient filters for manufacturing or processing items as common as cheese and milk, or for more sophisticated medical applications.

The discovery that fluids can move through nanotube membranes apparently could help move the process along.

"We tried many different fluids, but water actually flowed the fastest," Hinds said. "You really wouldn't expect that, because nanotubes are a form of graphite, and graphite doesn't like water. Water tends to bead up on it. Logic would suggest that the water would slow down, but it doesn't."

Two years ago, the group was using nanotube membranes only a few inches square. Now, Hinds says, UK's Center for Applied Energy Research has improved processes to the point that it can "grow" 900 square feet of nanotubes per day.

Hinds said researchers think the membranes could be produced for as little as 10 cents to 20 cents per square foot, making possible rapid, but also inexpensive, filtration systems. Now, U-Kentucky is looking for someone interested in investing in the process, he said.

"We're talking to some venture companies, but haven't gotten any firm commitments yet," he said. "It's a matter of finding a target that someone would want to be the first to invest in."

The Hinds research group in the Chemical & Materials Department is a relatively young group that is focused on the ultimate scaling of electronics and functional nano-structures to the molecular level. It is a cross-disciplinary research effort that borrows heavily from chemistry, physics, electrical engineering and materials science. The researchers say their success in nano-scale fabrication techniques would also have many creative applications outside of electronics such as bio-sensors and chemical separation membranes.

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