Molecular Dynamics Simulation on Collision Frictional Properties of a Molybdenum Disulfide (MoS₂) Film in Microgravity Environment

In this paper, a collision friction model for a double-layer MoS₂ film is proposed considering the microgravity induced collision in space environment. A modified REBO (Reactive Empirical Bond Order) potential is used to describe interactions among the atoms in the MoS₂ film. The collision friction process of the MoS₂ film is simulated by vibrations in the y and z directions, and the dependence of average friction force is analyzed. The influence of a single vibration in the y direction on the friction forces can be ignored, while the vibration in the z direction shows great influence. The effects of vibration frequency and amplitude on frictional behaviors of the MoS₂ film are investigated. The average friction forces during the collision friction process correlate with the frequency of the vibration in the z direction, and the relationship shows four stages. As the frequency increases, average friction forces show low values in the first stage, and they are increased as the frequency in the second stage. In the third stage, the average friction forces are decreased, and they come to a stable level in the fourth stage. Increasing the vibration amplitude at different frequencies leads to an increase in average friction force, due to that the increased amplitude results in a high indentation depth. The puckering phenomenon occurs at a specific frequency, which is a reason that the average friction force is increased during this collision friction process.