Lubrication Behavior of Fullerene-Coated Nanoparticles on Rough Surfaces.

Nanoparticles exhibit excellent lubrication properties and are utilized on rough interfaces to mitigate friction. This study investigates the lubrication behavior of composite C540 fullerene-coated silicon nanoparticles on rough silicon surfaces through all-atom molecular dynamics simulations (LAMMPS). The effects of key factors, including applied load, nanoparticle quantity, sliding velocity, and surface roughness, are systematically analyzed. Our results show that under high applied loads, increasing nanoparticle quantity effectively alleviates stress concentration, reducing both structural deformation and friction. However, excessive quantities cause pronounced protrusions that increase structural deformation. Velocity changes do not significantly impact friction or structural deformation, as the motion patterns of the probe and nanoparticles remain consistent. However, under low applied loads, probe-driven nanoparticle motion becomes the dominant factor in frictional energy dissipation. A positive correlation between the total kinetic energy of nanoparticles and friction force is observed across different roughness surfaces. The negative effects of excessive nanoparticles become more pronounced with increasing surface roughness. The optimal nanoparticle quantity is determined to be the minimum required to prevent stress-concentration-induced structural deformation. The optimal nanoparticle concentration reaches approximately 88.8% under high-load conditions, with each 3.55% increase in concentration resulting in a 0.45% reduction in structural deformation and a 0.59 nN decrease in friction. Under low-load conditions, the optimal concentration ranges from 15% to 30% across varying surface roughness levels, reducing friction by 30%-55% compared to the peak kinetic energy conditions. At low sliding velocities, nanoparticles fully adapt to substrate grooves, ensuring the probe and nanoparticles follow nearly identical interaction patterns at different velocities, making friction independent of sliding velocity. However, at high velocities, the nanoparticles act as abrasive particles, causing significant increases in both structural deformation and friction. On flat surfaces, friction is proportional to the applied load and remains independent of nanoparticle quantity. This study provides atomic-level insights into nanoparticle lubrication on rough surfaces, elucidating how nanoparticle concentration governs lubrication performance under varying conditions.