▎ 摘　　要

The feasibility of mass production of polycrystalline graphene (polygraphene) has motivated intensive efforts to boost its promising applications in electronics, energy storage, composites and biomedicine. As the grain boundaries in graphene-related 2D materials can strongly affect their material properties and the performance of graphene-based devices, it is highly desirable to better understand the effects of grain boundaries and make them as stable as possible. Here we employ molecular dynamics simulation to explore the annealing process of polygraphene and compare mechanical properties of annealed and unannealed polygraphene to pristine graphene under the same conditions, with a focus on the stability and energy of the grain boundaries. It is shown that the annealing process has a strong effect on the strength and stiffness of polygraphene due to the rearrangement and stabilization of the grain boundaries. However, our results show that irrespective of grain size, the annealing process makes polygraphene both tougher and stiffer, with a higher Young's modulus, strength, and ultimate strain under a tensile test compared to the same samples prior to the annealing process. (C) 2015 Elsevier Ltd. All rights reserved.