官能化对五边形石墨烯力学性能的影响及机理研究

Investigation of effects of functionalization on mechanical properties of penta-graphene

五边形石墨烯是近年来提出的一种完全由碳五元环组成的新型二维纳米材料.本文采用分子动力学方法研究了氢基、环氧基和羟基等官能团表面修饰及官能化率对五边形石墨烯力学性能和变形破坏机制的影响以及官能化对升温时五边形石墨烯结构转变的影响规律.研究发现,分别引入3种官能基团均可以有效地调控五边形石墨烯的力学性能和变形破坏机制.五边形石墨烯的杨氏模量和弹性极限均随官能化率的增大先剧烈减小再缓慢增大,而极限弹性应变单调递增.低官能化率五边形石墨烯在拉伸载荷下仍然表现出类似于完美五边形石墨烯的塑性变形破坏特征,不受约束升温时出现碳环结构转变,临界转变温度高于五边形石墨烯,而完全官能化可使五边形石墨烯由塑性向脆性变形破坏机制的转变,升温时五边形石墨烯并未出现碳环结构的转变.研究结果可为有效调控五边形石墨烯等二维纳米尺度材料的力学性能提供理论基础和结构设计依据.

Penta-graphene is a new two-dimensional metastable carbon allotrope composed entirely of carbon pentagons with unique electronic and mechanical properties.In this work,molecular dynamics simulations are carried out to investigate the effects of functionalization by hydrogen,epoxide or hydroxyl groups on the mechanical properties and failure mechanism of penta-graphene,as well as the effects of different functionalization coverages.The effects of functionalization on the structural transformation of free-standing penta-graphene triggered by increasing temperature have also been studied.The results indicate that each of the three functional groups considered can effectively tune the mechanical properties and the failure mechanism of penta-graphene.Both the Young's modulus and elastic limit of penta-graphene first decrease sharply and then increase slowly with the increase of the functionalization coverage,while the ultimate elastic strain increases monotonically.Like the pristine penta-graphene,partially functionalized penta-graphene still exhibits a plastic deformation failure behaviour under tensile load,which is caused by the irreversible pentagon-to-polygon structural transformation occurring during tensile loading.Temperature can trigger structural reconstruction for free-standing partially functionalized penta-graphene,and the corresponding critical transition temperature is higher than that of pristine penta-graphene.However,complete functionalization can change the deformation mechanism of penta-graphene from plastic deformation to brittle fracture.For fully functionalized penta-graphene by each of the three functional groups,the structural transformation is not observed when tensile strain is applied or environmental temperature is increased.These findings are expected to provide important guidelines for effectively tuning the mechanical properties of two-dimensional nanomaterials including penta-graphene.