BOFFINS HAVE COME UP with a new way of sorting carbon nanotubes by height, using really fast centrifuges.

The researchers, from the National Institute of Standards and Technology (NIST), a US-based federal technology institute, have been working on a technique that they claim will be able to provide industrial amounts of size-sorted nanotubes, vital for a large number of technological applications, which need very specific sizes of the tiny cylinders.

Carbon nanotubes, one atom thick sheets of carbon that curl up into tubes, are not particularly easy to sort. Producing the microscopic tubes is currently a process that means having to sift for them through a load of carbon clumps, sooty gunk and metal bits that are used as a catalyst. And then, even once all the mess is cleared away, the nanotubes still need size sorting because, although they’re tiny, a difference between tens of thousands of nanometers and hundreds of thousands can have serious implications for use in applications.

In microcircuits, for instance, the tubes need to be able to fit properly in order for the circuit to work, and in optical applications, light emission is determined by specific lengths of nanotube, making size sorting essential.

The NIST boffins based their research on previous work carried out in 2006, realizing that by spinning the nanotubes at high speeds in very dense fluid, using an ultracentrifuge tube, the nanotubes moved to their point of equilibrium based on buoyancy and friction determined by length.

Researcher Jeffrey Fagan noted that the process made the nanotubes effectively "run a race and the longer ones move farther in the same amount of time". The good thing about the whole process - aside from the fact that it helpfully also separates the nanotubes from all the rest of the gunk and junk - is that it is apparently fairly easy to scale up to mass commercial use, which would create huge quantities of pre-sorted nanotubes.

Who says size doesn’t matter, eh? µ

L'Inq
AZ Nanotechnology