Researchers at Oxford’s Clarendon Laboratory have found a way to separate different types of carbon nanotubes - something that is needed until a way of predictably making nanotubes is discovered.
So far, every production technique results in a mixture of single and multiwall nanotubes, of various diameters, and with various chiralities - the amount and direction of twist in the hexagon pattern along the tube.
Chirality determines, for example, whether the tube will be metallically conducting or semiconducting.
The Oxford team has discovered fluoro-polymers related to poly[9,9-dioctylfluorenyl-2,7-diyl] (PFO) that selectively wrap themselves around nanotubes, making them soluble and allowing them to be separated from unwrapped tubes in a simple centrifuge.
“The selectivity is sensitive to the dispersing polymer and also the solvent used to prepare the solution. Hence it is possible to tune the process to separate specific single-walled carbon nanotubes,” said Isis Innovation, the intellectual property licensing arm of the University of Oxford. “The effectiveness of the technique has been proven by photoluminescence emission spectroscopy, which is a powerful nanotube characterisation method.”
Altering the polymer backbone, or its side-chains, changes the diameter and chirality of the nanotubes selected.
At the moment, each polymer strongly selects one type of nanotube, plus a small proportion nanotubes similar in either diameter of chirality.
“Results obtained by using PFO show a much higher degree of selectivity than found with an existing commonly used method,” said Isis Innovation.
It is expected that polymers can be designed that are even more selective, and that methods can be devised to scale the separation up to commercial levels.