A Molecular Dynamics Simulation Study On Enhancement Of Mechanical And Tribological Properties Of Polymer Matrix By Introduction Of Carbon Nano Materials A Molecular Dynamics Simulation Study On Enhancement Of Mechanical And Tribological Properties Of Pol

Polymer materials are widely applied in agricultural science and technology,petrochemical,marine technology,aeronautics and astronautics,and advanced technology due to their excellent mechanical,thermodynamic properties,friction and wear resistance,light quality,corrosion resistance and low price.However,in practical applications,polymer materials are often subjected to lots of complex factors such as high temperature,high pressure,abrasive wear,et al.leading to less service life of the equipment and more economic losses due to the failures and wear of polymer matrix materials.Therefore,it is of great significance to explore the methods of improving the mechanical properties and failure mechanisms of friction and wear of polymer materials under external loadings.In present,traditional reinforcements,such as carbon black,silica and fiber are still widely applied.However,these reinforcements are usually nonrenewable,difficult to degrade,and low specific surface area.Environmental pollution and gaining weight are easily formed.The mechanical properties,friction and wear properties of polymer matrix can not to be enhanced efficientlys.Meanwhile,for research methods and means,calculations based on continuum theory and macroscopic experimental are still adopted.However,the micro structural conformations and changes of materials with the external loads from micro dimension can not to be observed and analyzed in real time.The theoretical analysis and supports in the micro dimensions are imperfection.In recent years,with the development of nanotechnology and material science,carbon nanotubes(CNTs)and graphene(GNS)are become to be ideal nano-reinforcements for the polymer materials due to their excellent mechanical and thermodynamic properties,high specific surface area and light quality.The limitations of traditional reinforcements can be improved.With the continuous combination of nanotechnology and computer technology,the theory of molecular dynamics(MD)is gradually developed.Hence,not only the trajectory of the atoms in the system,but also the microcosmic details in the process during simulations can be observed.The macroscopic properties of the material can also be calculated.In this paper,it is aimed to explore the mechanisms of the carbon nano-reinforcements to enhance the mechanical,friction and wear properties of the polymer matrix,and find means to improve these properties.The molecular models of CNTs and GNS reinforced polymer matrix are constructed respectively.The mechanical properties of composites are calculated via MD simulations.The simulation results show that the modulus of elasticity,shear modulus,tensile strength and hardness of the polymer matrix can be improved effectively by introduciton of CNTs and GNS as reinforcements.Based on the calculations and statistics of atomic concentration,radial distribution function,interface energy,and other micro information in the simulation processes,the mechanisms of the enhanced mechanical properties are discussed and revealed.It is found that van der waals and electrostatic forces from the surface of CNTs and GNS play an important role on the adsorption of the polymer chain,which improve the uniform transmission of the stress in the matrix leading to an effective continuous bridge in the crack,which can effectively resist the external loads and delay the crack propagation.Besides,the different effects between CNTs and GNS on enhancing the mechanical properites of polymer matrix are compared and analyzed.The molecular models of CNTs and GNS in same weight percetage reinforced polymer matrix are constructed.Pull-out behavior and tensile process are conducted respectively via MD simulations.The mechanisms of the difference between CNTs and GNS,and failure of materials are analyzed from the micro perspective.The simulation results show that the interfacial friction between GNS and polymer matrix is 1.2 times greater than that of the CNTs/polymer composites during the pullout behavior.The elastic modulus,tensile strength and surface crack energy of polymer matrix can be enhanced about 18%,8.7% and 5% respectively by introduciton of GNS than that of CNTs.By calculating and summarizing the microcosmic information in the simulation processes,it can be found that with the unique two-dimensional atomic configuration,GNS has a higher surface area than of CNTs,which larger surface adsorption force can be formed leading to a stronger reinforcing interface and ability to delay the failure of the polymer matrix fracture.Models of molecular frictional pairs between CNTs and GNS/ rubber composites and metal are constructed.The friction behaviors are simulated via MD simulations.Meanwhile,the friction behaviors under different pressure and frictional velocity are simulated accordingly.The friction coefficient and the wear rates are calculated.The micro information of atomic concentration distribution,interfacial energy,atomic velocity and temperature,atomic radial distribution function,molecular bond length and bond angle energy in the friction processes are calculated.The friction mechanisms between rubber composites and metal under different conditions,and the effects of CNTs and GNS on enhancing the tribological properties of composites are discussed.The results show that the rubber matrix is firmly adsorbed on the surface of carbon nanomaterials due to the van der waals and electrostatic forces from CNTs and GNS,which enhance the properties of stress transfer and shear deformation in the rubber matrix.In addition,the friction stresses,temperature and atomic motion activities around the friction interfaces are effectively reduced,and the friction resistance of the friction interface are improved.Finally,two noval nano-reinforcements of surface functionalized GNS and cross-linked GNS are proposed.Three different types of GNS reinforced polymer matrix composites are constructed respectively.The mechanical properties,thermal and tribological properties of these composites are calculated via MD simulations.The difference between the reinforcing interfaces in three kinds of matrices are explored,and the enhancement mechanisms are revealed from the microscopic perspective.The simulation results show that the polymer matrix can be attracted and bounded simutanously by the van der waals force,electrostatic force and crosslinked chemical bond on the surface of the crosslinked GNS.Stronger reinforcing interface can be provided leading to less movement activities of the polymer chain,and low free volume.The tensile behavior,thermodynamic properties and tribological properties of the polymer matrix can be improved accordingly.