Dynamic Behaviors\nof Confined Lubricant Molecules\nExplored via Molecular Dynamics Simulations

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