When people need a material that’s strong yet lightweight, they usually look to carbon fiber. In the near future, however, they may instead choose to go with composite materials made from stretched carbon nanotubes. These materials could theoretically offer the same strength as carbon fiber at one-tenth the weight, or the same weight at ten times the strength. Researchers from North Carolina State University have recently succeeded in creating such a composite.
According to the university, scientists have spent decades trying to achieve the four goals that must be met in order to create CNT (carbon nanotube) composites – the nanotubes must be long in order to effectively carry loads; they must be aligned in rows; there must be a high ratio of CNTs to the polymer or resin used to hold them together; and, in order for the material to bear weight evenly, the nanotubes must be as straight as possible.
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NC State’s Dr. Yuntian Zhu, a professor of materials science and engineering, is reportedly the first person to come up with a method of meeting all of these requirements.
The process begins by growing an array of long, skinny carbon nanotubes out of a flat substrate. Because the nanotubes aren’t rigid, they tend to flop over and lean against one another. The CNTs at one end of the array are then pulled sideways, causing all the other nanotubes to topple over in the same direction. As a result, they end up all being aligned.
The aligned array is then wound onto a rotating spool, simultaneously being stretched and being sprayed with a polymer solution that keeps the nanotubes bound together. This respectively results in a straightening of the nanotubes, and a high CNT-to-polymer ratio.
The finished product is a ribbon-like material, several bonded layers of which could supposedly be used to build anything from bicycle frames to aircraft. Because of the CNT-stretching process, that material has 90 percent more tensile strength and is 100 percent stiffer than it would be otherwise. Additionally, its thermal conductivity is almost tripled, while its electrical conductivity is boosted by 50 percent.
A paper on the research conducted by Zhu's team was recently published in the journal Materials Research Letters.
Source: North Carolina State University