Research On The Structure-activity Relationship And Friction Characteristics Of Base Oil And Additives

High-end lubricants are an indispensable part on the road towards 2035Intelligent Manufacturing in China.The structure-activity relationship between base oil and additives,the adsorption mechanism and wear reduction mechanism of lubricants all need to be further investigated to guide the production and development of new high-end lubricants.In this paper,the micro-scratch tester（MST2）was used to conduct micro-scratch tests on n-hexadecane base oil with Cu nanoparticle additives and Si O₂nanoparticle additives,and the changes in the tribological properties of the lubrication system were analyzed and compared.Using molecular dynamics（MD）simulation methods,a boundary lubrication model with nano-rough peaks was built,and the lubrication behaviors of n-hexadecane base oil added with Cu nanoparticle additives under different pressures,temperatures and shear velocities were studied.The adsorption model of nano-gap lubricating oil additives was established to study the influence of nano-roughness and base oil molecular structure on the adsorption process.The nanogap lubrication model with smooth iron wall was constructed to study the tribological properties of n-hexadecane base oil added Monooleate Glyceride（GMO）and Polyisobutylsuccinimide-Polyamine（PIBSA-PAM）under shearing at different pressures.The results show that:（1）The optimum concentration of Cu nanoparticle additives is about 0.5wt%,while that of Si O₂nanoparticle additives is about 0.1wt%;lubricants with nanoparticle additives can reduce the surface abrasion in the initial period of friction and wear,but it can cause the fluctuation of friction force.（2）In the lubrication systems with and without Cu nanoparticle additives,the n-hexadecane base oil is stratified,and with the increase of pressure,Cu nanoparticle additives have no obvious effect on the oil film stratification,but there is disturbance to the density distribution near Cu nanoparticles;under 100 MPa,the maximum wall stress of the lubrication system with Cu nanoparticle additives（19.4 GPa）is less than that of the lubrication system without Cu nanoparticle additives（26.12 GPa）;Cu nanoparticle additives improve the bearing capacity and wear resistance of the lubrication system,but increase the friction coefficient in the initial period of friction and wear,which is consistent with the experimental results;the lubricant film with Cu nanoparticle additives still shows good bearing capacity at high temperature and high shearing velocities.（3）The dense adsorption layer formed of base oil molecules near the wall inhibits the adsorption process between stearic acid molecules and solid wall;among the three base oils with the same carbon content and different molecular structures,when the nano-roughness is 0.2 nm,the friction coefficientμof the lubrication system is the minimum and the adsorption energy of stearic acid molecules is the maximum;stearic acid molecules are more easily dispersed in the base oil molecules with shorter branched chains.（4）There is competition of adsorption among GMO,PIBSA-PAM and n-hexadecane near the surface;the value of friction coefficientμis the minimum when the concentration of GMO is around 5.0wt%;when the lubricating system is sheared at different pressures,the GMO tends to adsorb on the surface,while PIBSA-PAM tends to disperse in the base oil.