Carbon nanotubes are generating lots of buzz because they are the strongest material known today. But their usage has been severely affected by the fact that it was not possible to isolate nanotubes with different properties.
Now, two teams of chemists from Rice University and the University of Illinois at Urbana-Champaign (UIUC) have found a way to separate and manipulate carbon nanotubes. Here are some quotes from these two news releases.
All single-walled carbon nanotubes are not created equal. There are 56 varieties, which have subtle differences in diameter or physical structure. Slight as they are these physical differences lead to marked differences in electrical, optical and chemical properties. For example, about one-third are metals, and the rest are semiconductors.
Although carbon nanotubes have been proposed for myriad applications — from miniature motors and chemical sensors to molecule-size electronic circuits — their actual uses have been severely limited, in part because scientists have struggled to separate and sort the knotted assortment of nanotubes that result from all methods of production.
To control nanotube chemistry, the researchers added water-soluble diazonium salts to nanotubes suspended in an aqueous solution. The diazonium reagent extracts an electric charge and chemically bonds to the nanotubes under certain controlled conditions.
By adding a functional group to the end of the reagent, the researchers can create a "handle" that they can then use to selectively manipulate the nanotubes. There are different techniques for pulling on the handles, including chemical deposition and capillary electrophoresis.
“Until now, the consensus has been that the chemistry of a nanotube is dependent only on its diameter, with smaller tubes being less stable and more reactive,” said Michael Strano, a professor of chemical and biomolecular engineering at UIUC. “But that’s clearly not the case here. Our reaction pathways are based on the electronic properties of the nanotube, not strictly on its geometric structure. This represents a new paradigm in the solution phase chemistry of carbon nanotubes.”
There are lots of possible applications for carbon nanotubes. One of them would be to build the space elevator forecasted by NASA, another catchy subject. The Guardian gives us new details in "The cheap way to the stars -- by escalator."
At the heart of a space elevator would be a cable reaching up as far as 100,000km from the surface of the Earth. The earthbound end would be tethered to a base station, probably somewhere in the middle of the Pacific ocean. The other end would be attached to an orbiting object in space acting as a counterweight, the momentum of which would keep the cable taut and allow vehicles to climb up and down it.
The biggest technical obstacle is finding a material strong but light enough to make the cable; this is where the carbon nanotubes come in. These are microscopically thin tubes of carbon that are as strong as diamonds but flexible enough to turn into fibre. In theory, a nanotube ribbon about one metre wide and as thin as paper could support a space elevator.
I sure wish this space elevator is built one day. For former stories about it, click here or there.
Sources: Rice University, September 11, 2003; Jim Kloeppel, University of Illinois at Urbana-Champaign, September 11, 2003; David Adam, The Guardian, September 13, 2003
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