Mechanical characteristics of individual multi-layer graphene-oxide sheets under direct tensile loading

The mechanical characteristics of graphene oxide (GO) play a critical role in its great applications. In this study, based on the experimental fracture data of individual multilayer free-standing GO sheets under tensile load, in combination with finite element analysis and molecular dynamics (MD) simulations, the failure strength, strain, and Young’s modulus are estimated to be 4–5 GPa, 8–15%, and 34–77 GPa, respectively. MD is used to disclose the effects of the structural characteristics of GO on the mechanical properties and failure mechanisms along both the armchair and zigzag directions. The failure strength and Young’s modulus of GO are found to slowly decrease with the increase in the ratio of hydroxyl and epoxy groups. The reason is that the breakage of sp3 bonds in the epoxy groups occurs prior to the breakage of sp3 bonds in hydroxyl groups. The former can lead to the formation of heptagonal rings that are able to sustain large strain and insignificantly implicate their surrounding bonds, whereas the latter may result in the complete fracture failure of GO. The fracture of multilayer GO sheets is initiated at the surface sheet due to the intrinsic absence of half-cooperative hydrogen bonding, which may lead to structural instability.