Nanotubes pass acid test

Jul 14, 2010

Rice University scientists have found the "ultimate" solvent for all kinds of carbon nanotubes (CNTs), a breakthrough that brings the creation of a highly conductive quantum nanowire ever 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 for his part in discovering the the family of molecules that includes the carbon nanotube. Rice is celebrating the 25th anniversary of that discovery this year.

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 fibers 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 fiber 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 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 , 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 said.

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," said Parra-Vasquez, who earned his Rice doctorate last year. "We hope this will open up new areas of research."

They also observed for the first time that long SWNTs dispersed by superacid form liquid crystals. "We already knew that with shorter nanotubes, the liquid-crystalline phase is very different from traditional liquid crystals, so liquid crystals formed from ultralong nanotubes should be interesting to study," he said.

Parra-Vasquez, now a postdoctoral researcher at Centre de Physique Moleculaire Optique et Hertzienne, Universite' de Bordeaux, Talence, France, came to Rice in 2002 for graduate studies with Pasquali and Smalley.

Study co-author Micah Green, assistant professor of chemical engineering at Texas Tech and a former postdoctoral fellow in Pasquali's research group, said working with long nanotubes is key to attaining exceptional properties in fibers because both the mechanical and electrical properties depend on the length of the constituent nanotubes. Pasquali said that using long nanotubes in the fibers should improve their properties on the order of one to two magnitudes, and that similar enhanced properties are also expected in thin films of carbon nanotubes being investigated for flexible electronics applications.

An immediate goal for researchers, 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."

Explore further: Researchers make nanostructured carbon using the waste product sawdust

More information: Read the abstract at: pubs.acs.org/doi/abs/10.1021/nn100864v

Related Stories

Breakthrough in industrial-scale nanotube processing

Nov 02, 2009

(PhysOrg.com) -- 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 ...

Rice Refining Production of Pure Nanotube Fibers

Sep 05, 2004

Rice University scientists are refining pioneering chemical production methods used to make pure carbon nanotube fibers. Research appearing in tomorrow's issue of the journal Science describes the scalable production techniques, which yield highly alig ...

High Value Semiconducting Carbon Nanotubes

Jul 12, 2004

A simple technique has been developed for producing high value semiconducting carbon nanotubes from samples of single and multi walled carbon nanotubes. The Oxford Invention is a technique for purifying samp ...

Recommended for you

Nanoparticle technology triples the production of biogas

Oct 22, 2014

Researchers of the Catalan Institute of Nanoscience and Nanotechnology (ICN2), a Severo Ochoa Centre of Excellence, and the Universitat Autònoma de Barcelona (UAB) have developed the new BiogàsPlus, a technology which allows ...

Research unlocks potential of super-compound

Oct 22, 2014

Researchers at The University of Western Australia's have discovered that nano-sized fragments of graphene - sheets of pure carbon - can speed up the rate of chemical reactions.

User comments : 4

Adjust slider to filter visible comments by rank

Display comments: newest first

PinkElephant
1 / 5 (1) Jul 14, 2010
An immediate goal for researchers, Parra-Vasquez said, will be to find "large quantities of ultralong single-walled nanotubes with low defects
Ha, is that all? Sounds easy enough... odd, that the worldwide R&D community still hasn't managed anything of the sort after more than a decade of effort. I wish them luck, and only with a tiniest bit of tongue in cheek.

Of course, it also remains to be seen whether long CNTs might approach, equal, or beat asbestos fibers in terms of carcinogenicity. Inquiring minds want to know... In the meantime, I hope the researchers are well stocked in, and enthusiastic users of, high-quality hazmat suits.
plasticpower
not rated yet Jul 15, 2010
I believe I read somewhere that carbon nanotubes have very similar properties to asbestos fibers, meaning that they can go through membranes of living cells and potentially mess with the DNA because of how tiny they are. So to answer your question, yes they are dangerous.
Jigga
not rated yet Jul 15, 2010
You can watch the video of nanotube fibber dissolving here:

http://www.youtub...5If2VU3Q

Graphene flakes could be dissolved in this "solvent" too. Actually the molecules of both substances are degrading by this operation a lot, so that this method may not be quite applicable for all purposes. The superacid makes cations from carbon atoms, which makes them prone to oxidation, cyclization and nucleophilic substitutions.
Jigga
not rated yet Jul 15, 2010
Maybe exactly the opposite approach could be more effective, i.e. dissolving the nanotubes in organometallic electron donors, like the sodium naphthalene complex in monoglyme, which could make an anions from nanotube molecules. This strongly reductive environment would protect these sensitive molecules against oxidation and substitutions, too..