▎ 摘　　要

Diffusion of water across surfaces generally involves motion on an uneven or defective but otherwise stationary substrate. Studying the diffusion of water nanodroplets on the surface of such a substrate is useful for the development and progress of nano-fluidic systems. In this study, the diffusion of water nanodroplets on doublevacancy graphene is investigated based on molecular dynamics simulations. We find that defects have a constraining effect on water nanodroplets. According to the defect distribution in conjunction with the range of water nanodroplet diffusion, the constraining effects can be differentiated as fully constrained or partially constrained. Subsequently, the impact on the constraining effects from water nanodroplet size and defect distance is studied. Tensile deformation and temperature are considered as two possible ways to break the constraining effects. The results show that the constraining effects from defects on water nanodroplets can be broken when biaxial tensile strain reaches 0.6% for both cases, but temperature has no obvious effect for partially constrained conditions. The differently constrained behaviors of water nanodroplets are found to be related to the vibration amplitude of the carbon atoms. Our results reveal that tensile deformation of graphene is more helpful for controlling the diffusion of water nanodroplets on double-vacancy graphene. The phenomena reported here can enrich the knowledge of molecular mechanisms for nanofluidic systems, and may inspire more applications with structural design for graphene and other 2D materials.