Molecular Dynamics Simulation Of Effects Of Nano-reinforced Materials On Friction And Thermodynamic Properties Of Butadiene Rubber

Butadiene rubber is a kind of high elasticity,electrical insulation and oil resistance of high polymer materials,because of these unique properties and is used as the basic material of friction parts,but often work in some harsh conditions,resulting in rubber fracture and wear.Therefore,it is necessary to improve the friction resistance of rubber.This paper aims to explore the internal mechanism of the influence of nano-reinforced materials on the friction and wear characteristics of rubber from the microscopic point of view.In this study,butadiene rubber was used as matrix,CNTs and GNS as reinforcing agents,and their effects on the mechanical and thermal conductivity of butadiene rubber were explored.The friction model between butadiene rubber and iron matrix was established,the mean azimuthal shift,relative atomic concentration and interface binding energy of polymer matrix were calculated and analyzed,and the microscopic reinforcing mechanism of carbon nanomaterials on composite rubber materials was analyzed.(1)Two models,Pure BR and CNTs/BR,were established.Compared with Pure BR,CNTs/BR composite matrix had a smaller free space,and the kinetic capacity of molecular chains was relatively weak.The glass transition temperature was increased by 5.56%,and it was found that the kinetic capacity of molecular chains of the two systems was continuously enhanced with the increase of temperature.The composite matrix filled with CNTs can reduce the migration of C atoms to the iron layer,and the peak temperature and velocity at the friction interface are 31.37% and 45% lower than those in Pure BR matrix,respectively.From the perspective of energy,it is stated that the binding energy between Pure BR matrix and iron layer is larger,which makes the rubber move more easily to iron layer.The friction coefficient of CNTs/BR matrix is lower than that of Pure BR matrix at different sliding speeds,and the friction coefficient decreases with the increase of speed.(2)The influence of CNTs to GNS on the thermal conductivity and friction properties of rubber was studied.The results show that the free volume fraction and mean azimuth shift of GNS/BR matrix are 6.7% and 7.69% lower than those of CNTs/BR matrix,respectively.The glass transition temperature increased by 6.16%.Thermal conductivity increased by 25.7%.In the three-layer friction model,the wear rate of GNS composite matrix is 7.9%,which is 9.6% lower than that of CNTs/BR composite matrix.The average atomic radial distribution function between GNS and rubber polymer is higher than that of CNTs matrix,and the relative atomic concentration of GNS matrix at the friction interface is 9.1% and 14.5% lower than that of CNTs matrix.The matrix can absorb more rubber molecular chains,reducing the space for the molecular chains to move,so that the wear resistance of the matrix is better than that of CNTs matrix.(3)The friction model between modified GNS and rubber composite matrix and metal elements was established,and the effect of modified GNS on the mechanical properties of rubber polymer materials was calculated by constant strain method.The free volume fraction of OH and COOH decreased by 8.3% and 10.3%,respectively.However,COOH modified GNS composite matrix has the lowest free volume fraction and mean azimuth shift.The glass transition temperature of COOH modified GNS composite matrix increased the most.Among the two modified GNS,COOH had the highest increase in volume modulus,shear modulus and mean Young’s modulus,which increased by 13.7%,20.7% and 37.2% respectively.In the process of friction,the matrix doped with COOH functional group has the lowest friction coefficient and the highest binding energy with rubber molecular chain.The results showed that the modified GNS enhanced the interaction with rubber molecular chains,making rubber molecular chains tightly clustered around the modified GNS,reducing the kinetic capacity and space of molecules,and weakening the movement of atoms in the matrix towards the friction interface,among which the COOH modification had the most obvious effect.In addition,when OH modified GNS is added to the composite matrix containing COOH,the free volume fraction decreases by 14.3%.The friction coefficient is reduced by 26.9%,and the Cooh-modified GNS intermediate matrix has greater motion capacity in the threelayer friction model,indicating that the mixed modified GNS can further improve the friction resistance of the material.Molecular dynamics simulation was used to reveal the mechanism of nanoreinforced materials improving the friction and thermodynamic properties of butadiene rubber.The research results of this paper can prolong the service life of rubber,reduce energy consumption,and provide a solid theoretical support for the preparation of high performance rubber.