Molecular dynamics study of ultrathin lubricant films with functional end groups: Thermal-induced desorption and decomposition

Molecular dynamics simulation is employed to study the thermal durability and stability of molecularly thin lubricant films with functional end groups. A coarse-grained polymer model that describes intrinsic bond breakage is presented. Using this novel model, we investigated the bead number density profile to quantify the lubricant weight loss that occurs during heat treatment process. The density profile, which was partially computed by a hyperbolic tangent function, reveals that both the liquid–vapor interfacial thickness and the solid–vapor separation increase with temperature. Nonetheless, the liquid phase diminishes at high temperatures and the solid–vapor separation begins to decay as the temperature increases further. We also investigated the lubricant weight and bond loss profiles to provide an insight on the thermal instability of nonfunctional and functional lubricant films. Our simulation results show that the functionality of the lubricant film can greatly influence lubricant desorption albeit a slight effect on lubricant decomposition. For both nonfunctional and functional thin lubricant films, lubricant desorption is the domination depletion process and is attributed as the root for lubricant degradation and failure.