It is hoped that new techniques for thermoelectric power generation using relatively low-temperature waste heat such as motor vehicle exhausts will lead to improved energy efficiency. However, the deterioration of the junction between the cold and hot electrodes and the thermoelectric conversion element in such devices is a major problem.
One potential solution may be found through the use of single-wall carbon nanotubes (SWNTs), which are mechanically flexible and have high thermal conductivity. It is expected that SWNTs vertically aligned in a film will provide a superior thermal interface.
A collaborative research project by Professor Shigeo Maruyama at the University of Tokyo Graduate School of Engineering, Professor Ken Goodson at Stanford University and Professor Rong Xiang at Sun Yat-sen University demonstrated the direct measurement of in-plane elastic modulus (a measure of how easy it is to deform a material) of vertically aligned SWNTs.
It was found that the mechanical properties differed greatly between the randomly-ordered edge of the film and the highly-oriented body. Through the measurement of the resonance of a micro-cantilever covered with vertically aligned SWNTs and simulations by coarse-grained molecular dynamics method, it was revealed that zipping (weak Van Der Waals attraction between adjacent SWNTs in the highly-oriented body) and entanglement of carbon nanotube bundles (in the randomly-ordered edge) are the dominant determinants of the material’s elastic properties.
Such analysis of SWNT arrays is expected to be extended to future studies of the thermal and electric properties of flexible thin film transistors, solar cells, and transparent conductive films made of SWNTs.
Source: Tokyo University