November 10, 2009 – Researchers from the US and Israel say they have figured out how to make pure carbon nanotube (CNT) fibers at an industrial scale, based on "tried-and-true" processes from the chemical industry for producing polymer fibers.
The work, detailed in the journal Nature Nanotechnology, involved 18 researchers from Rice U.’s Richard E. Smalley Institute for Nanoscale Science and Technology (the late Smalley is actually listed as a co-author), the U. of Pennsylvania, and the Technion-Israel Institute of Technology. It builds on work done in 2003 to dissolve large amounts of pure CNTs in strong acidic solvents, finding the CNTs in such solutions can self-align to form liquid crystals, which could then be spun into monafilament fibers, establishing "an industrially relevant process for nanotubes that was analogous to the methods used to create Kevlar from rodlike polymers, except for the acid not being a true solvent," said Wade Adams, director of the Smalley Institute and co-author of the new paper.
The new work focuses on identifying what Adams calls "a true solvent" for CNTs: chlorosulfonic acid, in which CNTs were seen to "dissolv[e] spontaneously," proved by direct imaging of vitrified fast-frozen acid solutions, according to paper co-author Matteo Pasquali, Rice professor in chemical and biomolecular engineering and in chemistry. Studying how CNTs behave in acids, with the background knowledge of polymers and rodlike colloids, the Rice team came up with experimental techniques to examine the results and describe solutions of rods; Technion’s team developed the methodology to produce high-res images of the CNTs dispersed in the acid using electron microscopy at cryogenic temperatures.
What’s so important about devising a "true solvent" for CNTs? "Plastics is a $300B industry because of the massive throughput that’s possible with fluid processing," said Pasquali, noting that "polymers can be melted or dissolved and processed as fluids by the train-car load. Processing nanotubes as fluids opens up all of the fluid-processing technology that has been developed for polymers."