Researchers spin carbon nanotubes into usable fibers


New material retains strength and properties of single-walled carbon nanotubes

PHILADELPHIA Materials scientists from the University of Pennsylvania and chemists from Rice University report the first large-scale manufacture of fibers composed solely of single-walled carbon nanotubes (SWNTs) in the Sept. 3 issue of the journal Science. This new material is a macroscopic realization of many of the amazing mechanical, electrical and thermal properties of nano-scale ideal nanotubes.

"Throughout the relatively brief history of carbon nanotube research, the creation of a usable nanotube fiber has been one of the ultimate goals," said John E. Fischer, co-author of the study and professor of Materials Science and Engineering in Penn's School of Engineering and Applied Sciences. "Its applications are nearly limitless, from replacing copper wiring to creating super-strong fabrics to, as some have suggested, building the cable tethers that will allow space elevators to travel from the earth to orbit."

The main obstacle to creating a usable SWNT fiber comes from the very properties that make SWNTs so attractive. Individually, these carbon nanotubes are stronger than steel, conduct electricity better than copper and conduct heat better than diamond. Together, however, they tend to clump together in otherwise unusable bunches, largely impervious to the heating used to melt polymers and spin them into fibers.

The solution to the problem, developed by Rice's Richard E. Smalley, the 1996 Nobel Laureate in Chemistry, co-discoverer of the Carbon60 "buckyball" form of carbon, and a recipient of a PhD (honoris causa) from Penn in 2002, involved dispersing nanotubes in sulfuric acid. Once separated into individuals, the tubes can then be re-assembled more compactly, like a box of soda straws, and then extruded into highly aligned fibers.

The Rice technique of spinning SWNT fibers was inspired by the process used to create other modern super fibers such as Kevlar -- the material used in bulletproof vests -- and Zylon -- a material twice as strong as Kevlar. Using these by now conventional spinning techniques, the researchers extruded the dispersion through a long hypodermic needle, allowing the resulting strand to coagulate before removing the acid.

As a result, the researchers transformed disorganized nanoscale materials into a continuous macroscale fiber. Each individual strand of the SWNT fiber is approximately 100 micrometers in diameter (several human hairs) and contains about a million close-packed and aligned nanotubes.

Fischer and his Penn colleagues determined the nature and structure of the nanotube/acid dispersion and resulting fiber. Penn doctoral student Wei Zhou identified the local structure of tubes in the acid dispersion, a critical step in understanding how the process works. Juraj Vavro and Csaba Guthy, also doctoral students, measured the electrical and thermal conduction properties respectively, correlating them with the degree of SWNT alignment in the fibers as measured by Zhou. The fibers possess good mechanical and electrical properties, but only modest thermal conductivity up to now.

"Like any new discovery, it will be a number of years of further research and refinement until we begin seeing the first application of these fibers," Fischer said. "In the meantime, other applications are further along and will hopefully maintain the level of interest and excitement in this fascinating new class of materials."

Source: Eurekalert & others

Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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