Proc. Roy. Soc. Lond. A, 467, 1270-1289 (2011) [pdf]

Compressive Dynamic Scission of Carbon Nanotubes under Sonication: Fracture by Atomic Ejection

H.B. Chew, M.-W. Moon, K.-R. Lee and K.-S. Kim

We report that a graphene sheet has an unusual mode of atomic-scale fracture due to its structural peculiarity, i.e. single sheet of atoms. Unlike conventional bond-breaking tensile fracture, a graphene sheet can be cut by in-plane compression which is able to eject a row of atoms out-ofplane. Our scale-bridging molecular dynamics simulations and experiments reveal that this compressive atomic-sheet fracture is the critical precursor mechanism of cutting single-walled carbon nanotubes (SWCNTs) by sonication. The atomic-sheet fracture typically occurs within two hundred femtoseconds during the dynamic axial buckling of a SWCNT; the nanotube is loaded by local nanoscale flow drag of water molecules caused by micro-bubble collapse during sonication. This is on the contrary to common speculations that the nanotubes would be cut in tension, or by high temperature chemical reactions in ultrasonication processes. The compressive fracture mechanism clarifies previously unexplainable diameter-dependent cutting of the SWCNTs under sonication.