Credit: © 2006 APS

A quantitative understanding of the strength of carbon nanotubes (CNTs) is important for their use in the synthesis of robust materials. However, there is still insufficient direct experimental data to validate theoretical predictions of the mechanical properties of CNTs. The role of kinks in CNT deformation is of particular interest and researchers in the US have now investigated this phenomenon in individual nanotubes at elevated temperatures.

J. Y. Huang and colleagues1 from Boston College, University of Michigan-Flint, Harvard University and Massachusetts Institute of Technology, heated single (S), double (D) and multiwalled (MW) CNTs by passing electric currents through them. The high bias voltages used in this study are thought to heat CNTs to temperatures in excess of 2,000 °C. When uniaxially stressed at these temperatures, the motion of kinks in individual CNTs could be monitored with transmission electron microscopy. Kink motion was observed in all of the CNTs, suggesting that this is a universal plastic deformation mode under these conditions. The velocity of kink motion was fastest in DWCNTs (6 nm s-1) and slowest in MWCNTs (0.7 nm s-1). Because the direction of kink movement was found to be independent of the polarity of the applied field, it is thought that the process is related to thermal stress rather than electronic effects. Furthermore, kink motion was not observed at room temperature.

These observations demonstrate that CNTs are highly ductile at elevated temperatures, and are likely to have significant implications in the design and synthesis of high-strength materials based on these structures.