Rice University scientists today unveiled a method for the industrial-scale processing of pure carbon-nanotube fibers that could lead to revolutionary advances in materials science, power distribution and nanoelectronics. The result of a nine-year program, the method builds upon tried-and-true processes that chemical firms have used for decades to produce plastics. The research is available online in the journal Nature Nanotechnology.
The new process builds upon the 2003 Rice discovery of a way to dissolve large amounts of pure nanotubes in strong acidic solvents like sulfuric acid. The research team subsequently found that nanotubes in these solutions aligned themselves, like spaghetti in a package, to form liquid crystals that could be spun into monofilament fibers about the size of a human hair.
"That research established 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 current research shows that we have a true solvent for nanotubes -- chlorosulfonic acid -- which is what we set out to find when we started this project nine years ago."
Following the 2003 breakthrough with acid solvents, the team methodically studied how nanotubes behaved in different types and concentrations of acids. By comparing and contrasting the behavior of nanotubes in acids with the literature on polymers and rodlike colloids, the team developed both the theoretical and practical tools that chemical firms will need to process nanotubes in bulk.
From Nature Nanotechnology:True solutions of single-walled carbon nanotubes for assembly into macroscopic materials
Translating the unique characteristics of individual single-walled carbon nanotubes into macroscopic materials such as fibres and sheets has been hindered by ineffective assembly. Fluid-phase assembly is particularly attractive, but the ability to dissolve nanotubes in solvents has eluded researchers for over a decade. Here, we show that single-walled nanotubes form true thermodynamic solutions in superacids, and report the full phase diagram, allowing the rational design of fluid-phase assembly processes. Single-walled nanotubes dissolve spontaneously in chlorosulphonic acid at weight concentrations of up to 0.5wt%, 1,000 times higher than previously reported in other acids. At higher concentrations, they form liquid-crystal phases that can be readily processed into fibres and sheets of controlled morphology. These results lay the foundation for bottom-up assembly of nanotubes and nanorods into functional materials.
19 pages of supplemental information
1. Sample preparation to measure Raman D/G ratio after acid dispersion
2. Evidence of individual SWNT by Cryo-TEM
3. Determination of the isotropic phase concentration
4. Determination of the nematic phase concentration
5. Different liquid-crystalline morphology observed in biphasic solutions in acids where the Raman G peak shifts by dG ≥ 21 cm-1
6. Dissolution of SWNT fiber in chlorosulfonic acid
7. Irregular fibers spun from chlorosulfonic acid into viscous coagulants
8. Additional notes on modeling
9. Additional notes on fiber spinning
10. Additional notes on crystal solvate phase
11. Diameter and length distribution
12. Boundaries between LC/LC+S and I+CS/CS+S phases
13. Supplementary movies
A Page with links to the supplemental movies and power points