Researchers Spin Carbon Nanotubes Into Usable
Fibers;
New Material Retains Strength and Properties of Single-Walled
Carbon Nanotubes
September 02, 2004
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.”
Co-authors on the Science article from Rice University include
Richard E. Smalley, Robert H. Hauge, Matteo Pasquali, W.E.
Billups, Howard Schmidt, Wen-Fang Hwang, Carter Kittrell,
Sivarajan Ramesh, Rajesh K. Saini, Haiqing Peng, Booker, Virginia
A. Davis, Lars M. Ericson, Myung Jong Kim, A. Nicholas G.
Parra-Vasquez, Hua Fan, and Yuhuang Wang, Joseph Sulpizio,
and Gerry Lavin. Funding for this research was provided by
the Office of Naval Research and the Department of Energy.
Contact:
Greg Lester
215.573.6604
glester@pobox.upenn.edu
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