nanoknot
Image: Science

Scientists in France report in today's issue of Science that they have developed a new process for spinning continuous carbon fibers that are finer and stronger than most other known materials. Indeed, these threads--comprised of single-wall carbon nanotubes (SWNT)--can be made as tiny as a few micrometers in diameter, and they are tough enough to be tied into tight knots without breaking (see micrograph).

Philippe Poulin, Brigitte Vigolo and their colleagues used SWNTs, in the form of bundles of a few nanotubes, as the raw material in their novel manufacturing process. To separate and disperse the individual nanotubes uniformly, they put them in a surfactant solution of sodium dodecyl sulfate (SDS). At the right concentrations, the SDS coated the tubes enough to counterbalance the van der Waals attractions keeping them clumped together in bundles.

Next they slowly injected this SWNT dispersion through a syringe needle or thin glass capillary into a swirling solution of polyvinylalcohol (PVA). The PVA solution acted to quickly recondense the tubes, probably by displacing some of the SDS adsorbed on their surfaces. And because the tubes were all aligned in the direction of flowing solution when they again stuck together, they formed a nanotube mesh. Slowly pulling the mesh from the bath made it collapse into a high-density ribbon.

Nanotechnologists have suggested a number of potential applications for such materials over the years, ranging from tethers connecting satellites to Earth to nanotube-based supercapacitors and electrochemically driven artificial muscles. Now they have a seemingly reliable, readily scalable method for producing them.