(Nanowerk News) Researchers at the UCLA Henry Samueli School of Engineering and Applied Science have been awarded $4.5 million over four years by the U.S. Department of Defense to strengthen carbon nanotube yarns and sheets, materials that hold great promise for advancing satellite technology.
Carbon nanotubes are molecular-sized tubes of carbon with remarkable properties. They are among the stiffest, strongest and most tenacious fibers known and also have properties valuable in areas like nanotechnology, electronics and optics. Tests have shown that the strongest single-wall carbon nanotubes are more than 500 times as strong as steel.
Since their discovery in 1993, carbon nanotubes have attracted great academic and industrial interest, but commercial applications have been slow to develop, primarily because of lingering technical problems that reduce the nanotubes' strength.
Now, a group of UCLA researchers led by Larry Carlson, head of UCLA's Easton Institute of Technology Advancement and director of new materials at UCLA Engineering, intends to correct various technical issues, potentially making the yarns and sheets 10 times stronger.
The group used seed money from a donation by James L. Easton, formerly of Easton Sports Inc., to generate early results at UCLA and to align its research with the government's need for strong, multi-functional materials in space.
Co-principal investigators on the project include Robert Hicks, a UCLA professor of chemical and biomolecular engineering, and Suneel Kodambaka, a UCLA assistant professor of materials science and engineering. Three outside companies will also be partners on the project: Nanocomp Inc., Surfx Inc. and Materia Inc.
Carbon nanotube materials are sought after for various structural applications because they are so strong and yet so light. Reducing just a single pound in a satellite can save up to $75,000 in fuel, additional structures needed to carry the satellite's mass and its fuel mass, and other costs. The nanotube-based materials have the added benefit that they can conduct heat and provide electrical shielding better than the materials they replace. This can reduce a satellite's mass even further, since other support systems can be reduced or omitted altogether.
So why hasn't this been done?
When combined into a composite, carbon nanotubes degrade to about 1 percent of their original measured strength. Furthermore, when yarns are spun out of carbon nanotube fibers, the yarn becomes less than 20 percent as dense as theory would dictate. Lastly, the fibers are currently held together by relatively weak forces, which tend to slide and pull out under tension, causing the yarn to pull apart.
The researchers plan to use atmospheric pressure plasma to carefully open up individual carbon bonds without compromising the overall strength of the nanotubes. They will also attach special organic molecules that can join to carbon bonds on one side and resin on the other.
"Instead of hitting the nanotubes with a sledge hammer," said Hicks, who will oversee plasma and surface modification, "we can go in there with a finely tuned surgical knife and create the exact functionalization we need to achieve a high degree of cross-linking without any loss of structural integrity."
The team will also use a special resin consisting of tiny sub-nanometer rings that can fit between all the nanotubes instead of simply draping long molecules on the surface. The resin has a viscosity similar to that of water, so it flows easily. The resin will provide control over the reaction, creating a super-tough, cured resin inside the structure.
In addition, the team will bond certain types of atoms with the carbon nanotubes to reinforce how the fibers are held together.
"Our approach is simple, scalable and can potentially improve not only the mechanical strength but also the toughness of the carbon nanotube yarns," said Kodambaka, an expert in materials synthesis and processing.
"Here is a case where a sporting goods investment, enhanced with government support, could add to the nation's satellite technology, giving lighter launch loads and tougher space structures," Carlson said. "While this might seem backwards, with volume production and lower costs, it would be gratifying to bring it all back to sports."