Engineering professor aids in important nanotech advance

9/15/2008 - By: Guia Del Prado

Jonghwan Suhr, an assistant professor of mechanical engineering, recently published his research findings on Continuous Reinforced Carbon Nanotube Composites in Nano Letters, a prominent academic journal in the field of Nanotechnology.

Suhr said his study of continuous reinforced carbon nanotube composites brings him a step closer to his hope of bio-mimicking artificial muscles or skins, which can be applied to a wide variety of fields.

The project is a continuation of Suhr's previous work on nanotubes, which was published in Nature Nanotechnology. In this previous work, Suhr tested the strength and fatigue behavior of carbon nanotubes. He collaborated with Lijie Ci and Pulickel Ajayan from Rice University in Houston, Texas and Victor Pushparaj from Resnselaer Polytechnic Institute in Troy, N.Y. Together, they grew millimeter-long nanotube arrays, which are composed of vertically aligned carbon nanotubes in a block. Once the carbon nanotubes arrays were made, they were tested for strength and fatigue behavior.

Nanotubes generally have diameters ranging from a few nanometers to a few hundred nanometers. Because of their strength, carbon nanotubes can be used for mechanical structures and biomedical applications.

In the previous project, Suhr and his colleagues found that the nanotube can exhibit soft tissue-like behavior. The nanotube arrays have a porosity of around 95 percent, meaning that carbon nanotubes only occupied five percent of the arrays while 95 percent of the array was occupied by air.

In this most recent project, Suhr filled the air space with a soft polymer. The result was a continuous reinforced carbon nanotube composite.

"People have been working for more than ten years intensively [on carbon nanotube composites]," Suhr said. "Nobody had had a chance to study continuous nanotube composites...but we made it."

The new composite demonstrates impressive results. The previous carbon nanotubes were too short for continuous fibrous composites and used for a few applications. With the new composite, Suhr was able to grow the nanotubes several millimeters long. The reinforced carbon nanotube composite's strength increased by 3,400 percent and 2,100 percent in damping, which is the capability of a material to absorb energy resulting from mechanical oscillations or noise.

"Most materials show compromise between two properties - strength and damping," Suhr said. "But this particular system showed an increase in both."

In addition, the continuous composites are lightweight, flexible, have mechanical robustness, outstanding fatigue resistance, electrical and thermal conductivities and also has tissue-like behavior, Suhr said.

While Suhr is interested in the mechanical uses for the composite, he is also exploring the use of the composite for mimicking muscle tissue. Suhr is currently working with the aircraft company, Boeing, to investigate creating artificial skin made from continuous reinforced carbon nanotube composites for wing structures of unmanned air vehicles. Suhr said he hopes the artificial skin on unmanned air vehicles will decrease wind resistance to the vehicle, which will result in energy efficiency. Suhr also hopes to develop artificial skin to apply to wind turbine blades to increase energy efficiency for the renewable energy systems.

Suhr's plan for the new composite also includes biological applications. He hopes to make the inactive material electro active. This would eliminate the need for many mechanical parts in a mechanism.

"This fascinating soft tissue-like material can be made into an electroactive polymer," Suhr said. "So that we don't have to add mechanical motors, which is typically heavy. So maybe we can develop bio-mimicking artificial muscles using this material."

Suhr and his colleagues' advance in creating a new nanotube composite material lead to a new frontier in nanotechnology. It makes Suhr's future plans in mimicking muscles and producing new mechanical and structural applications possible.

"We need new material to break through our state of art technology," Suhr said. "There are many interesting nanomaterials whose properties have not been fully understood yet. We may want to explore them and understand the fundamentals so as to be utilized for emerging applications such as next generation aircraft or alternative energy systems."


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