[FoRK] U. T. Dallas-led research team produces strong, transparent carbon nanotube sheets

Damien Morton fork
Sat Aug 20 04:49:28 PDT 2005



RICHARDSON, Texas (Aug. 18, 2005) - University of Texas at Dallas (UTD) 
nanotechnologists and an Australian colleague have produced transparent 
carbon nanotube sheets that are stronger than the same-weight steel 
sheets and have demonstrated applicability for organic light-emitting 
displays, low-noise electronic sensors, artificial muscles, conducting 
appliqu?s and broad-band polarized light sources that can be switched in 
one ten-thousandths of a second.

Carbon nanotubes are like minute bits of string, and untold trillions of 
these invisible strings must be assembled to make useful macroscopic 
articles that can exploit the phenomenal mechanical and electronic 
properties of the individual nanotubes. In the Aug. 19 issue of the 
prestigious journal Science, scientists from the NanoTech Institute at 
UTD and a collaborator, Dr. Ken Atkinson from Commonwealth Scientific 
and Industrial Research Organization (CSIRO), a national laboratory in 
Australia, report such assembly of nanotubes into sheets at commercially 
useable rates.

Starting from chemically grown, self-assembled structures in which 
nanotubes are aligned like trees in a forest, the sheets are produced at 
up to seven meters per minute by the coordinated rotation of a trillion 
nanotubes per minute for every centimeter of sheet width. By comparison, 
the production rate for commercial wool spinning is 20 meters per 
minute. Unlike previous sheet fabrication methods using dispersions of 
nanotubes in liquids, which are quite slow, the dry-state process 
developed by the UTD-CSIRO team can use the ultra-long nanotubes needed 
for optimization of properties.

Strength normalized to weight is important for many applications, 
especially in space and aerospace, and this property of the nanotube 
sheets already exceeds that of the strongest steel sheets and the Mylar 
and Kapton sheets used for ultralight air vehicles and proposed for 
solar sails for space applications, according to the researchers. The 
nanotube sheets can be made so thin that a square kilometer of solar 
sail would weigh only 30 kilograms. While sheets normally have much 
lower strength than fibers or yarns, the strength of the nanotube sheets 
in the nanotube alignment direction already approaches the highest 
reported values for polymer-free nanotube yarns.

The nanotube sheets combine high transparency with high electronic 
conductivity, are highly flexible and provide giant gravimetric surface 
areas, which has enabled the team to demonstrate their use as electrodes 
for bright organic light emitting diodes for displays and as solar cells 
for light harvesting. Electrodes that can be reversibly deformed over 
100 percent without losing electrical conductivity are needed for high 
stroke artificial muscles, and the Science article describes a simple 
method that makes this possible for the nanotube sheets.

The use of the nanotube sheets as planar incandescent sources of highly 
polarized infrared and visible radiation is also reported in the Science 
article. Since the nanotube sheets strongly absorb microwave radiation, 
which causes localized heating, the scientists were able to utilize a 
kitchen microwave oven to weld together plexiglas plates to make a 
window. Neither the electrical conductivity of the nanotube sheets nor 
their transparency was affected by the welding process -- which suggests 
a novel way to imbed these sheets as transparent heating elements and 
antennas for car windows. The nanotube sheets generate surprisingly low 
electronic noise and have an exceptionally low dependence of electronic 
conductivity on temperature. That suggests their possible application as 
high-quality sensors - which is a very active area of nanotube research.

"Rarely is a processing advance so elegantly simple that rapid 
commercialization seems possible, and rarely does such an advance so 
quickly enable diverse application demonstrations," said the article's 
corresponding author, Dr. Ray H. Baughman, Robert A. Welch Professor of 
Chemistry and director of the UTD NanoTech Institute. "Synergistic 
aspects of our nanotube sheet and twisted yarn fabrication technologies 
likely will help accelerate the commercialization of both technologies, 
and UTD and CSIRO are working together with companies and government 
laboratories to bring both technologies to the marketplace."

The breakthroughs resulted from the diverse expertise of the article's 
co-authors. Dr. Mei Zhang and Dr. Shaoli Fang, NanoTech Institute 
research scientists, first demonstrated the nanotube sheet fabrication 
process, and this result was translated into diverse applications by the 
entire team. The other team members include Dr. Anvar Zakhidov, 
associate director of the NanoTech Institute; Christopher Williams, 
Zakhidov's graduate student from the UTD Physics Department; Dr. Sergey 
Lee and Dr. Ali Aliev, research scientists at NanoTech Institute, in 
addition to Atkinson and Baughman.

The applications possibilities seem even much broader than the present 
demonstrations, Baughman said. For example, researchers from the 
Regenerative Neurobiology Division at Texas Scottish Rite Hospital for 
Children, Dr. Mario Romero, Director, and Dr. Pedro Galvan-Garcia, 
Senior Researcher Associate, and Dr. Larry Cauller, associate professor 
in UTD's neuroscience program, have initial evidence suggesting that 
healthy cells grow on these sheets - so they might eventually be applied 
as scaffolds for tissue growth.

Baughman said that numerous other applications possibilities exist and 
are being explored at UTD, including structural composites that are 
strong and tough; supercapacitors, batteries, fuel cells and 
thermal-energy-harvesting cells exploiting giant-surface-area nanotube 
sheet electrodes; light sources, displays, and X-ray sources that use 
the nanotube sheets as high-intensity sources of field-emitted 
electrons; and heat pipes for electronic equipment that exploit the high 
thermal conductivity of nanotubes. Multifunctional applications like 
nanotube sheets that simultaneously store energy and provide structural 
reinforcement for a side panel of an electrically powered vehicle also 
are promising, he said.

UTD researchers began collaborating with their counterparts at CSIRO 
last year. In November 2004, the organizations achieved a breakthrough 
by downsizing to the nanoscale methods used to spin wool and other 
fibers to produce futuristic yarns made from carbon nanotubes.

The latest research was funded by the Defense Advanced Research Projects 
Agency, an agency of the United States Department of Defense, the U.S. 
Air Force Office of Scientific Research, the Texas Advanced Technology 
Program, the Robert A. Welch Foundation and the Strategic Partnership 
for Research in Nanotechnology.

More information about the FoRK mailing list