Molecular Dynamics Simulation of Adsorption and Friction of Constrained Lubricating Films on Rough Gold Substrates

Molecular dynamics simulations were conducted to investigate the effects of constraint conditions and lubricant types on the adsorption and frictional performance of a rough gold substrate. The study compared the relative strengths of cohesion within mixed clusters and adhesion between the clusters and the substrate. The constraint condition was implemented by imposing a moving wall along the negative z-axis during the initial adsorption stage, thereby restricting the molecular motion until a designated position was reached, after which the constraint was removed. Simulation results indicate that, under constrained conditions, the adsorption film is uniformly distributed over the substrate, whereas under unconstrained conditions, the film is distributed irregularly. Compared to the unconstrained case, the constrained adsorption film exhibits improved friction and wear performance. Furthermore, using graphene nanosheets (GNSs) alone as a lubricant favors reduced substrate friction but is detrimental to wear, while perfluoropolyether (PFPE) alone results in higher friction levels but lower substrate wear. The combination of GNSs with PFPE appears to balance these effects, contributing to both lower friction and reduced wear. The same conclusion can be drawn by substituting silver and copper for gold. These findings provide theoretical guidance for the development of advanced space-lubrication technologies.