The mechanical behavior of a unique type of multi-walled carbon nanotube, and an acid-treated version of this multi-walled carbon nanotube type that had nanoscale defects on their surfaces arising from the acid treatment, were reported. These defects, in scanning electron microscope and transmission electron microscope imaging had a channel-like appearance, as if a ring of material was cut away from the multi-walled carbon nanotube around the circumference. The mechanical properties of individual multi-walled carbon nanotubes were shown experimentally to depend strongly upon their structure, and structural disorder could markedly reduce the mechanical properties. Tensile-loading experiments using a nanomanipulator tool inside a scanning electron microscope revealed that the tensile strengths of 10 pristine multi-walled carbon nanotubes ranged from ∼2 to ∼48GPa (mean of 20GPa). For 10 acid-treated multi-walled carbon nanotubes with channel-like defects, the tensile strengths ranged from ∼1 to ∼18GPa (mean of 6GPa); roughly 70% lower than those of pristine multi-walled carbon nanotubes. Microstructural observations revealed that the fracture of acid-treated multi-walled carbon nanotubes occurred at a channel-like defect region in 8 of the 10 samples. This indicated that the channel-like defects associated with the acid etching were typically the weakest points in the acid-treated multi-walled carbon nanotube structure, and that stress concentration was present at the defect region.

The Influence of Nanoscale Defects on the Fracture of Multi-Walled Carbon Nanotubes under Tensile Loading. G.Yamamoto, J.W.Suk, J.An, R.D.Piner, T.Hashida, T.Takagi, R.S.Ruoff: Diamond and Related Materials, 2010, 19[7-9], 748-51