Dynamic Behaviors of Confined Lubricant Molecules Explored via Molecular Dynamics Simulations

Abstract

Perfluoropolyethers (PFPEs) and multiply alkylated cyclopentanes (MACs) are frequently used lubricants in space due to their high stability under demanding conditions. In this article, we make a comparison between these two lubricants and reveal the effect of temperature on lubrication via molecular dynamics simulations. First, PFPE exhibits slip motion, while MAC exhibits sticky flow under the same pressure. This is because MAC has a larger adhesion energy and smaller Voronoi volume, and the flat and stiff structures also restrict the momentum transfer. Second, we explore the influence of temperature, and the results indicate that the increase of temperature has a similar influence on film as the introduction of shearing velocity. An atom-locked zone appears near the bottom surface at low temperatures due to the inadequacy of momentum transfer. The existence of the locked zone increases the inhomogeneous distribution of viscosity and further increases the friction force and the coefficient of friction. Our research provides insight into the lubrication mechanisms of these materials and guidance for the development of advanced lubrication technology for application in space.