Rice University scientists have found the “ultimate” solvent for all kinds of carbon nanotubes (CNTs): chlorosulfonic acid, which can dissolve half-millimeter-long nanotubes in solution, they reported this month in the online journal ACS Nano. This is a critical step in spinning fibers from ultralong nanotubes, and a breakthrough that brings the creation of a highly conductive quantum nanowire closer.

Nanotubes have the frustrating habit of bundling, making them less useful than when they’re separated in a solution. Rice scientists led by Matteo Pasquali, a professor in chemical and biomolecular engineering and in chemistry, have been trying to untangle them for years as they look for scalable methods to make exceptionally strong, ultralight, highly conductive materials that could revolutionize power distribution, such as the “armchair quantum wire.”

The armchair quantum wire — a macroscopic cable of well-aligned metallic nanotubes — was envisioned by the late Richard Smalley, a Rice chemist who shared the Nobel Prize for his part in discovering the the family of molecules that includes the carbon nanotube.

A few years ago, the Rice researchers discovered that chlorosulfonic acid, a “superacid,” adds positive charges to the surface of the nanotubes without damaging them. This causes the nanotubes to spontaneously separate from each other in their natural bundled form.

This method is ideal for making nanotube solutions for fiber spinning because it produces fluid dopes that closely resemble those used in industrial spinning of high-performance fibers. Until recently, the researchers thought this dissolution method would be effective only for short single-walled nanotubes.

In the new paper, the Rice team reported that the acid dissolution method also works with any type of carbon nanotube, irrespective of length and type, including multiwalled nanotubes (MWNTs), as long as the nanotubes are relatively free of defects.

An immediate goal for researchers, primary author Nicholas Parra-Vasquez said, will be to find “large quantities of ultralong single-walled nanotubes with low defects — and then making that fiber we have been dreaming of making since I arrived at Rice, a dream that Rick Smalley had and that we have all shared since.”

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