The Stanford paper represents about five years of teamwork centered in the Stanford Mechanical Engineering Department including experiments led by first author Yoonjin Won, who was then a doctoral student in mechanical engineering.
She used a variety of existing techniques to assemble CNTs with different structural characteristics, and then measured the flexibility (also called modulus) and thermal conductivity of each structure to look for the optimal structure.
Left to nature, the carbon atoms that form CNTs will create structures that if we could see them -- resemble a bowl of spaghetti.
But Won worked with collaborators at the University of Tokyo to create CNTs that grew up relatively straight, like grasses. Some degree of entanglement still occurred. Precise control of CNT growth remains beyond the reach of science.
Nevertheless, Won's experiments showed that longer CNTs, grown less densely together, seemed to have the best combination of flexibility, heat conductivity and strength, for use in electronics and other industrial applications where thermal stress is expected.
To some degree her findings represent a tradeoff. Denser, shorter CNT structures are stronger and more efficient at dissipating heat. But they are also more entangled and stiffer. Won's experimental results showed that as CNT strands grew longer, they tended to grow straighter and were less tangled, which increased the flexibility of the structure, albeit with some acceptable losses in the other two parameters.
Because the ultimate goal of this work is to reveal how to optimize CNT structures for use as thermal transfer materials, the Stanford team built
|Contact: Tom Abate|
Stanford School of Engineering