Nanotubes Pass Acid Test

Researchers at Rice University unveiled a new method for dissolving half-millimeter-long carbon nanotubes in solution, a breakthrough that could pave the way to the development of highly conductive quantum nanowire. 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 revolutionise power distribution and lead to the development of 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.

Pasquali, primary author Nicholas Parra-Vasquez and their colleagues reported this month in the online journal ACS Nano that chlorosulfonic acid can dissolve half-millimeter-long nanotubes in solution, a critical step in spinning fibres from ultralong nanotubes.

Current methods to dissolve carbon nanotubes, which include surrounding the tubes with soap-like surfactants, doping them with alkali metals or attaching small chemical groups to the sidewalls, disperse nanotubes at relatively low concentrations. These techniques are not ideal for fibre spinning because they damage the properties of the nanotubes, either by attaching small molecules to their surfaces or by shortening them.

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 fibre spinning because it produces fluid dopes that closely resemble those used in industrial spinning of high-performance fibres. 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, as long as the nanotubes are relatively free of defects.

Parra-Vasquez described the process as “very easy.”

“Just adding the nanotubes to chlorosulfonic acid results in dissolution, without even mixing,” he says.

While earlier research had focused on single-walled carbon nanotubes, the team discovered chlorosulfonic acid is also adept at dissolving multiwalled nanotubes (MWNTs). “There are many processes that make multiwalled nanotubes at a cheaper cost, and there’s a lot of research with them,” says Parra-Vasquez, who earned his Rice doctorate last year. “We hope this will open up new areas of research.”

More information on the research is available from Rice University’s News & Public Relations department.

The abstract is available here.

Tags: nanotechnology, nanotubes, Rice University