Stronger, better materials are a nanotube away

January 4th, 2011  |  by  |  Published in Features, Jan. 2011

man in white coat in laboratory

Mehrdad Ghasemi Nejhad in the lab where carbon nanotubes are made.

Since the Hawaiʻi Nanotechnology Laboratory was established in the University of Hawaiʻi at Mānoa’s College of Engineering in 2003, the group has made the Guinness Book of World Records for producing the world’s smallest brush, developed new nano materials, dramatically improved composite materials and launched a start-up company to develop proprietary materials in Hawaiʻi.

At the heart of each development is carbon nanotubes, microscopic marvels that hold the potential to improve the performance of products from wind turbines to fuel cells.

A nanometer is one-millionth of a millimeter—about 50,000 times finer than the average human hair—so manipulation is a tricky business, says lab director Mehrdad Ghasemi Nejhad, professor and chair of mechanical engineering.

Japanese physicist Sumio Iijima made the first nanotube in 1991. Carbon nanotubes form on a silicon-oxide coated silicon wafer when a source of carbon, such as xylene, is combined with a liquid containing a catalyst, such as iron, cobalt or nickel, on a silicon wafer and baked at very high temperature. The iron particles precipitate as the liquid evaporates, creating islands on the wafer. The carbon atoms settle on the iron particles, building up in hollow cylindrical structures held together covalently in nature’s strongest chemical bond.

“The key for achieving desired properties for a host material or structure is finding the right form, amount and integration technique for the nanomaterial,” Nejhad says.

Nanotubes form the bristles of the group’s record-book brush, which could be used to clean micro-electromechanical systems as well as micro-capillaries, separate harmful ions from industrial waste waters or paint surfaces with molecule-thin coats.

Get the carbon nanotubes to grow in the form of forests, and you have the potential to “turn fiber cloths super strong,” he continues. Composite materials, such as fiberglass polyester and carbon epoxy, combine a fiber system with a polymer system for increased strength and performance. But cracks can form and propagate between the layers, causing the composite to delaminate.

Postdoctoral researchers work with Nejhad to improve composite material performance in two ways. Vamshi Gudapati is tackling the carbon nanotube forests that strengthen the fiber materials. Richard Russ is perfecting the polymers that hold composite layers together. Picture Velcro reinforced with Super Glue. Or, rather, imagine it. You’ll need a high-resolution electron microscope to see it, and some secret steps in the process to ensure uniform and bubble-free dispersal.

The payoff, Nejhad says, is that carbon fibers are almost the same strength as steel, but just a third of the weight. Carbon nanotubes are 50–100 times stronger than steel. When integrated into polymers or onto the fibers, they result in nanocomposites with 100- to 400-percent property improvements over their traditional counterparts, such as carbon epoxy. “Hence, we can use them anywhere composites are used, from boats to automobiles to spacecraft, with much better performances and durability,” he says. Reduced weight translates into decreased costs.

Consider the wind turbine. The energy it produces is proportional to the length of its blades, which are essentially ribbed, skin-covered structures like airplane wings. Longer blades are subject to higher stresses as they turn, which can cause them to fail. Glass epoxies allowed engineers to increase blade length to 150 feet, and graphite epoxies, to about 300 feet. Nanocomposite blades could potentially double that, Nejhad says.

Nanotechnology also has applications in fuel and solar cells. For example, Nejhad envisions someday painting the roof of homes with a nanomaterial-based thin film to capture solar energy without the need for more costly silicon-based photovoltaic cells.

Improving hydrogen fuel cell performance and durability is key to making hydrogen a more feasible alternate fuel. A proton exchange membrane fuel cell requires a hydrated membrane, two electrodes and two catalyst layers, usually carbon paper coated with platinum, to split hydrogen gas into proton and electron. Completing the circuit produces electric energy, with water as the by-product. Using hydrophobic carbon nanotubes as the electrodes and catalyst layer bed increases surface area, electrical conductivity and hydrophobicity for the catalytic reactions. This reduces the need for auxiliary humidification equipment, in turn reducing size, weight and costs for the fuel cells.

Postdoctoral researcher Atul Tiwari has been working on the production of graphene nanosheet, a flat version of the cylindrical carbon nanotube but with much higher surface areas. High surface-to-volume ratio and super properties could improve the durability, performance and efficiency of batteries and supercapacitors while reducing their weight, size and costs. Four undergraduate and four graduate students round out the lab staff.

An American Society for Mechanical Engineers Fellow and associate editor of the Journal of Thermoplastic Composite Materials, Nejhad holds several patents. He has received support from the U.S. Congress and Office of Naval Research and serves as co-principal investigator with Chair of Electrical Engineering Tony Kuh on a renewable energy initiative involving 20 faculty members that is primarily funded by the U.S. Department of Energy and UH Mānoa Office of the Vice Chancellor for Research and Graduate Education.

In addition to his university research, Nejhad is the founder and chief technology advisor of Honolulu-based Adama Materials, Inc. The company received a $4.75 million venture investment from Artiman Ventures and Startup Capital Ventures in September 2010. Tim Dick of Startup Capital Ventures serves as CEO.

“Adama represents the ideal model of cross-disciplinary development of technology, business and law at UH and demonstrates how UH discoveries can be successfully transferred to industry,” says Jonathan Roberts of the UH Office of Technology Transfer and Economic Development.

nanotubes under an electron microscope


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