The influence of nanoscale defects on the fracture of multi-walled carbon nanotubes under tensile loading

We report the mechanical behavior of a unique type of multi-walled carbon nanotube (MWCNT) and an acid-treated version of this MWCNT type that have nanoscale defects on their surfaces from the acid treatment. These defects, from scanning electron microscope (SEM) and transmission electron microscope (TEM) imaging have a ‘channel-like’ appearance, as if a ring of material was cut away from the MWCNT around the circumference. The mechanical properties of individual MWCNTs have been experimentally shown to strongly depend on their structure and structural disorder can drastically reduce the mechanical properties. Tensile-loading experiments using a nanomanipulator tool operated inside a SEM revealed that the tensile strengths of 10 pristine MWCNTs ranged from ∼ 2 to ∼ 48 GPa (mean 20 GPa). For 10 acid-treated MWCNTs with channel-like defects, tensile strengths ranged from ∼ 1 to ∼ 18 GPa (mean 6 GPa, thus roughly 70% lower than those of the pristine MWCNTs). Microstructural observations revealed that the fracture of the acid-treated MWCNTs occurred at a channel-like defect region in 8 of the 10 samples. This indicates that the channel-like defects associated with the acid etching are typically going to be the weakest points in the acid-treated MWCNT structure and that stress concentration is present at the defect region.