Carbon Nanotube Versatility
Ranging from a potential new water desalination technology to airplane wings that can diagnose and heal their own cracks, several projects led by Nikhil Koratkar, associate professor of mechanical engineering, are demonstrating the usefulness and versatility of carbon nanotubes.
As part of a four-year NSF grant, Koratkar’s team showed for the first time that it is possible to precisely control the flow of water through carbon nanotube membranes, an important step toward a filtration technology that will be useful in water desalination, environmental restoration, or biomedical research. Nanotube membranes can exhibit high flow rates and high selectivity, but they are hydrophobic, strongly repelling water.
Koratkar overcame that problem by applying a small positive potential to the membrane and a negative potential to the water.
The membrane immediately began pumping water through the minuscule hollow nanotubes. By reversing the charge, the flow could be stopped.
Koratkar said the membrane gained the ability to pump water because of local water electrolysis, with oxygen atoms coating the surface of the nanotubes, temporarily eliminating the hydrophobic nature of the membrane. When the charge was reversed, oxidation stopped.
In another project funded by NSF and the Army, Koratkar is relying on the electrical properties of carbon nanotubes to develop new high-performance polymer materials for aircraft wings and other structures. These materials make it possible to identify small cracks and repair them in real time.
The team made a structure from common epoxy, added multi-walled carbon nanotubes, and built in a nanotube wire grid that could both measure electrical resistance and apply current. A small amount of electricity was sent through the nanotubes, constantly monitoring electrical resistance. When cracks appeared, resistance went up in that spot. By increasing the current, the temperature in that area was raised so that a healing agent embedded in the epoxy melted, curing the crack.
See also: Using Nanotubes To Detect and Repair Cracks in Aircraft Wings
(Rensselaer Research Review)