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The effective dispersion of carbonaceous soot has a critical effect on the friction and wear properties and thus decreases energy waste and equipment trouble. Molecular dynamics (MD) simulation and experimental study are performed to unravel the dispersion behavior and mechanism of soot agglomerate in lubricating system with effect of dispersant concentration at various pressures and temperatures. The static, confinement and shear models were created with dispersant polyisobutylsuccinimide polyamine (pib). At static conditions, pib molecules could approach and then self-assemble on soot fragments to disperse soot agglomerate. Under confinement conditions with an external pressure imposed, soot dispersion was better than that under static conditions, and the effect of pressure was not remarkable. The best dispersion characteristic was obtained as dispersant increased to 10 wt% exceeding that the dispersants were excessive and induced their self-aggregation. Under shear conditions, 10 wt% pib molecules showed the best dispersion at both 300 K and 373 K, which is considered as a critical value for soot dispersion from the perspective of MD simulations. Finally, the tribological experiments provided a prime validation for MD simulations. The most effective lubrication occurred in 12.5 wt% sample with friction and wear reduction by 51% and 80% compared to 10 wt% sample, respectively, due to the well soot dispersion and possible friction modification of dispersants. [Display omitted] • Dispersion of carbonaceous soot is studied by MD simulation and experiment. • Dispersive and interactive mechanisms are revealed in different models. • Good soot dispersion benefits the reduction in friction and wear. [ABSTRACT FROM AUTHOR]

[Display omitted] • Traction behavior and mechanism are studied by molecular dynamics simulations. • The velocity profile indicates a typical shear localization due to ordering structure. • The traction performance depends on molecular structure and sliding velocity. • Power transmission mechanism is attributed to interlocking, cross-linkage and rotation-resistance effects. The traction mechanism in power transmission systems with effects of sliding velocity and molecular structure are revealed at high temperature and pressure through molecular dynamics approach. Firstly, the simulated traction coefficients agree well with the experimental values, and the linear correlation between traction coefficient and bond energy is created to predict the coefficient. The molecule with higher bond energy and more –CH 3 groups between two terminal cyclohexane rings shows higher traction coefficient. Then, the typical shear localization is found from the layered structure of alicyclic molecules confined between Fe 2 O 3 slabs. The increase of sliding velocity has a very week effect on the velocity profile but benefits the slip length shrinkage on the whole. The traction coefficient increases fast and then converges toward a plateau with increasing velocity. Finally, the power transmission mechanism in molecular level is discussed and attributed to three effects, i.e., the interlocking effect between alicyclic rings in layer, the cross-linkage effect between layers, and the rotation resistance effect of alicyclic structure. This mechanism is desirable to be achieved with low degrees of slip, and thus maximize the efficiency of the device and help designing new traction fluids. [ABSTRACT FROM AUTHOR]

[Display omitted] • Deformation mechanism and tribology properties of Cu/Ta bilayer and multilayer are studied by MD simulations. • The interface significantly impacts the dislocation nucleation and propagation. • The thicker monolayer benefits dislocation propagation and facilitates surface wear. • The preferred accumulation of worn Ta atoms is observed. Molecular dynamics simulations are adopted to study the deformation mechanism and friction and wear properties of Cu/Ta bilayer and multilayer during a nanoscratching process. The results indicate that in bilayer the Cu/Ta interface adsorbs and blocks dislocation propagation, while the Ta/Cu interface acts as an emission source of dislocations. In multilayers (particularly for thickness δ = 25 Å), the dislocation could overleap the hard Ta layer and then nucleate in the next Cu layer although the friction shear is still in the first Cu layer, indicating the deformation transition of plasticity-elasticity-plasticity across Cu/Ta/Cu layers due to stress transfer. The increase in monolayer thickness facilitates dislocation propagation and deformation recovery, as well as surface removal quantified by wear volume. Severer plastic deformation and surface removal occur in Cu layer while higher friction appears in Ta layer. The preferred accumulation of worn Ta atoms in the left front, up to 80% in δ = 45 Å multilayer and 60% in others, is observed and attributed to the nonsymmetrical slip directions. The differences in plastic deformation and tribological property indicate a critical thickness of about 25 Å used to guide the ultraprecise manufacture of Cu interconnections in microdevices or semiconductor industry. [ABSTRACT FROM AUTHOR]