A new lower limit for the bond breaking strains of defect-free carbon nanotubes: Tight binding MD simulation study

Abstract: The Order (N) Tight Binding Molecular Dynamics (TBMD) algorithms applied to simulate the tensile elongations of short (2-2.5 nm) armchair and zigzag Single Walled Carbon Nanotubes (SWCNTs) without bond breakings or defect formation. Simulations are repeated at high temperatures. We fix the lower limit of breaking strains to short SWCNTs without bond breaking or 5-7 defects formation. At room temperature, the simulated (4,4) SWCNT is able to carry the strain up to 130% of the relaxed tube length without bond breaking or 5-7 defects formation. This value is 127% for (11,0) SWCNT, 125% for (17,0) SWCNT, 123% for (10,10) SWCNT. In defect free, short nanotubes as the nanotube's radius increase the bond-breakings occur at lower strain values regardless of their chirality. This is true when we heat the tubes to higher temperatures. Bond breaking strain values, tensile strength, Young's modulus of the SWCNTs are obtained as functions of temperature. Defect free zigzag nanotubes exhibit higher tensile strength than armchaired ones. Young's modulus of defect free individual singlewall nanotubes is found to be in the range of 0.400 TPa within the elastic limit. At room temperature and experimentally realizable strain values, thinner tubes are more resistant to bond breaking and zigzag tubes over armchair ones. At high temperatures although the resistance to strain drops the same trend still holds. We observe a slight decrease of the tensile strength with increasing temperatures. The same trend is also observed in the Young's modulus. Results are important in determining a true breaking strains of SWCNTs.