Stress Relaxation Behaviors Of Macro-scopically Assembled Graphene Materials

Graphene,a two-dimensional(2D)material with high mechanical strength,high electrical conductivity and thermal conductivity,shows its great potential in energy,electronic device,smart wearing and construction material fields.A key issue is to make microscopic graphene into macroscopically assembled graphene materials(MAGMs)with intrinsic property of graphene,which is always a hot topic for scientists.For structural materials,besides high mechanical strength and modulus,the durability property is also required in particular cases,especially fatigue and relaxation behaviors.However,much attention has been paid to the effect of relationship between intrinsic structure and performances,improving the static mechanical strength,toughness and modulus,and studying the fracture and deformation behaviors of MAGMs.Only few reports noticed the importance of fatigue and relaxation behaviors in MAGMs.Accordingly,this dissertation focused on the stress relaxation behaviors of MAGMs,and presented systematic research on the relationship between micro structures and macroscopic performances.The main research contents are listed as follows.1.We observed a fatal stress relaxation of graphene bucky papers and depicted the structural origin of the stress relaxation.The relaxation behavior of graphene materials,a typical 2D macromolecular system,well-conforms to a Maxwell structural model as in describing polymeric materials.This work will be very useful to deepen the understanding on the static and dynamic behaviors of macroscopically assembled materials of graphene and other 2D nanomaterials.2.We proposed an interlayer crosslinking strategy to conquer stress relaxation of graphene papers and fabricated a highly elastic graphene paper with a large strain,designed through depressing the relaxation trend,in analogy of vulcanization to produce polymeric elastic rubber.The elastic graphene paper showed a break elongation over 20%,accompanied with energy loss coefficient about only 0.2.3.We studied the stress relaxation behavior of graphene fibers and proposed a semicrystalline fiber model.To conquer stress relaxation,plasticization stretching and heat treatments were introduced to pristine graphene oxide fiber.The optimized graphene fiber exhibited excellent performances,including tensile strength of 1.7GPa,Young’s modulus of 298 GPa.After relaxation for 12 hours,over 98% stress could be remained.4.We studied the mechanical and relaxation properties of graphene aerogels made by freeze dried and hydro-plastic foaming methods.We analyzed the relationship between fabrication methods and internal structure of aerogel.We fabricated a conductive graphene aerogel with high elastic and fatigue resistance,holding the potential in sensor and mechanical cushion.In summary,this dissertation systematically studied the stress relaxation behaviors of MAGMs,provide effective programs to release relaxation and proposed rational models to describe the stress relaxation and internal structure of MAGMs.Our work made significance to deepen the understanding of MAGMs and played an important role in promoting the real applications of MAGMs as structural material.