This illustration shows a micro-material called carbon nanotubes which grow like trees, and after being compressed spring back to their original shape.
UH researchers stretch limit of nanotubes' strength
The tiny fiber shows promise for electronics and everyday items
A UNIVERSITY OF HAWAII-MANOA researcher has discovered that microscopically thin fibers known as carbon nanotubes are more resilient and hundreds of times stronger than commonly used synthetic foams.
Carbon nanotubes are long, thin cylinders of carbon that are 50,000 times thinner than the human hair yet have incredible strength, said Anuyan Cao, a professor in the UH-Manoa Department of Mechanical Engineering.
Nanotubes are very small, less than 50 nanometers in diameter, with 1 nanometer measuring one-billionth of one meter, he said. They can be seen only with an electron microscope, he said.
Research on nanotubes is still in the very early stages. However, the material could have applications in construction and electronics, as well as more mundane uses in items such as plastic utensils, rubber gloves, furniture, electronic games and toys, according to a UH-Manoa press release.
Scientists have studied nanotubes extensively since they were discovered in 1991 "because they have so many fascinating properties," Cao said in an interview.
He said his team found for the first time that by aligning a huge number of nanotubes, they can be grown "like trees in a forest, standing upright, making a whole field."
They can be compressed to 15 percent of their original thickness and spring back to the original shape after removing the force, "which means nanotubes are very resilient," he said.
They can be bent and folded repeatedly, and they will not collapse or lose basic strength, he said.
"Many conventional materials, if you compress them too much, they can't recover their original shape. Nanotubes are different. They have excellent mechanical properties, which has been proved by previous theoretic and experimental studies."
Nanotubes are very strong, Cao said. "You cannot break them. At the same time, they are very flexible." A nanotube can be bent like a bow and will bounce back, he said.
Initially, people could do only theoretical modeling, he said.
However, advanced atomic force microscopes, which have a very small, sharp tip, enable scientists to dip into a nanotube sample and investigate its mechanical behavior, he said. Other methods also have been developed to press nanotubes on a structure with a lot of holes and see how they respond, he said.
"In our case, we presented a very simple experiment using a huge number of nanotubes," Cao said.
His team compressed a film with nanotubes and put it in a testing instrument to see how the film compressed and rebounded.
When first compressed, the cylinders straighten up again, but after being compressed hundreds of times, they develop permanent zigzag buckles with some deformation, Cao said.
Nanotube buckles, shown above, are a way to make nanotubes stronger. UH professor Anuyan Cao says nanotubes are about 50,000 times thinner than human hair but have incredible strength.
The advantage of buckling is the material is like springs, he said. "It is this buckle that can be compressed, rebound and recover, but they do not break. They are very resistant to fatigue.
"We compressed them repeatedly, thousands of cycles, and they didn't lose much strength. They have amazing property."
Another interesting phenomenon, Cao said, is that the nanotubes buckle in the same direction at the same wavelength, "unanimously in the same shape."
The researchers compared properties of nanotube films with conventional plastic foams such as those made of latex rubber or polyurethane.
"The strength of nanotubes is hundreds of times higher than foams," Cao said. "To make a real product, maybe it is still far away, but we can see potential applications."
RIGHT NOW, he said, nanotube material can be used in microelectronics.
Nanotube springs can be used as activators, and nanotube film can be coated on a small electronic device to absorb energy and protect it, he said.
Cao has applied for a patent and is continuing research on nanotube foam-film.
He said the strength of the buckling material depends on the wavelength. If it is larger, the buckle is weaker. If smaller, the buckle will be stronger.
"Depending on the applications, some require less strength; some, high strength. If we can control the wavelength, we can design a sample particularly for application."
Cao joined UH in July, coming here from Rensselaer Polytechnic Institute in Troy, N.Y., where he was a postdoctoral researcher.
The findings of Cao and his team -- including Mehrdad Ghasemi-Nejhad, also in the UH-Manoa Department of Mechanical Engineering, and two colleagues at the University of Florida -- were published in this week's issue of Science magazine.