“To produce large objects out of nanotubes, chemical processes must use a liquid that can disperse large concentrations of pristine tubes,” said Matteo Pasquali of Rice University. “Based on our findings, we believe that superacids can be used to make macroscale fibres and sheets of nanotubes using methods that are quite similar to those in widespread use by the chemical industry.”

To carry out the technique, the researchers dissolved single-walled carbon nanotubes in a superacid - 102% sulphuric acid. The mixing process took at least three days. In this way, they made solutions containing up to 10% carbon nanotubes by weight, a concentration more than 10 times higher than achieved by methods that use polymer additives or detergents.

“As the concentration [of nanotubes] increases, the nanotubes first align themselves into spaghetti-like strands, and eventually they form tightly packed liquid crystals that can be processed into pure fibres,” said Pasquali.

The scientists found that quenching a 4 wt.% nanotube solution into ether and filtering it produced a “bucky-paper” of entangled “super-ropes” about 300-1000 nm thick. The nanotubes were aligned inside the super-ropes, but the super-ropes were not aligned with each other.

In the presence of small amounts of water, meanwhile, the liquid-crystal phase of the nanotube solution separated into needle-shaped strands containing highly aligned single-walled carbon nanotubes. The strands were about 20 microns long and roughly 0.5-1 micron in diameter. The scientists dubbed these structures “alewives” because of their resemblance to a particular type of fish.

In the absence of water, the researchers were able to process the liquid-crystalline phase into highly aligned fibres of pure single-walled nanotubes by extruding the dispersion through a syringe needle into an ether bath, without using any surfactants or polymers.

The researchers reported their work in Macromolecules.