A Molecular Dynamics Study On Mechanical And Frictional Properties Of Graphene/Polymer Composites

PTFE is broadly used in agriculture and industry,spaceflight,electronic technology and other fields because of its excellent chemical stability,corrosion resistance,anti-aging properties and friction properties.However,PTFE still suffers from inferior mechanical properties and abrasion rate,which limits its wider application.Graphene,as a new 2D nanocarbon material,has high mechanical and tribological properties,and can be used as an ideal filler to complement the mechanical and tribological properties of polymer composites.There have been numerous experimental studies on the mechanical and frictional properties of graphene-reinforced PTFE,but due to the limitation of microscopic testing techniques,the mechanism about the effect of graphene on the mechanical and tribological properties of PTFE matrix still needs to be further explored.In this work,the mechanical and frictional properties of PTFE,Graphene/PTFE composites and FG/PTFE composites were calculated using molecular dynamics simulations to disclosure the principle of the effects of Graphene and FG on the mechanical and frictional properties of PTFE,which provides a theoretical basis for the design of polymer composites with excellent mechanical and frictional properties.The research content and main conclusions of this paper are as follows:(1)The tensile and compressive processes of PTFE system were studied using uniaxial tensile and uniaxial compression simulation methods.The results show that with the gradual increase of tensile strain,the stress in the tensile direction first rises and then falls,and there are obvious voids in the system,and when the strain reaches 100%,only a few PTFE molecular chains exist in the middle position of the system.As the compressive strain increases,the PTFE molecular chains keep moving in the compressive direction,making the structure of the model in the compressive direction gradually tighten;meanwhile,the tensile strength of PTFE gradually increases with the increase of strain rate.The friction process between PTFE and metal Fe was simulated,and the microscopic property changes of PTFE during the friction process were analyzed.As the load increases,the friction coefficient of pure PTFE decreases gradually decreases.In addition,the friction coefficient of PTFE increases and then decreases with increasing friction speed.(2)The results of calculations of mechanical and frictional properties of Graphene/PTFE composites show that the addition of Graphene with a mass fraction of 3.5 wt.% to PTFE not only destabilizes the stable structure of PTFE itself,making the system more prone to internal defects such as holes during the stretching process,but also enhances the motion of PTFE molecular chains during the stretching process,making the composite The tensile strength of the composite decreases and the elongation at break is also reduced.In addition,the addition of Graphene reduces the motion of PTFE molecular chains during compression and limits the motion of molecular chains,resulting in an increase in the compressive strength of Graphene/PTFE composites.During the friction process,Graphene forms an enhanced interface in the composite,PTFE molecular chains are adsorbed near Graphene,the number of PTFE molecules in contact with metal Fe is reduced,the interaction between PTFE composite matrix and metal Fe is weakened,the energy dissipation at the friction interface is reduced,which makes the temperature of the junction lower,and at the same time Graphene will slides along the friction direction,which enhances the motion of PTFE molecular chains in the friction process,making it easier for PTFE composites to slide during the friction process,thus improving the frictional properties of PTFE.(3)The FG/PTFE composites were modeled and its mechanical and frictional properties were calculated.Among them,the fluorine content of FG was 28.6%,33.7% and 41.3%,respectively.The results show that FG can effectively reduce the molecular chain movement ability of PTFE composites during tensile and compression,and hinder the deformation of the model,thus improving its tensile and compressive properties.Meanwhile,the addition of FG can further reduce the number of atoms interacting with metal Fe during the friction process of PTFE composites,reduce the interaction between them at the friction interface,and improve the friction performance of the composites.In addition,the mechanical and frictional properties of FG/PTFE composites were enhanced gradually with the increase of FG content.