[SY-O8] Friction mechanism of nanostructured steel in lubricant: A coarse-grained molecular dynamics study
Intensive studies have been dedicated to the problem of boundary lubrication in recent years. Experimental studies have demonstrated a significant reduction in friction coefficients of steel that has nanostructured surfaces. It is conjectured that nanostructured metals have a large density of sites with strong attraction to lubricant molecules, resulting in reduced friction. The detailed mechanism of the phenomenon however remains unclear.
To reveal the mechanism of lubrication between metal surfaces, atomic- or molecular-level investigations are required for the effect of metal-molecule interaction on boundary lubrication. Coarse-grained molecular dynamics (CGMD) is a useful and efficient simulation method to tackle such problems. Indeed, a CGMD study of shear flow of lubricant molecules between metal surfaces showed that the more molecules were adsorbed on the surfaces, the lower the friction coefficient became. Nevertheless, molecular-level mechanisms are not fully understood regarding the experimentally presented effect of the surface nanostructure on the friction coefficient or the nature of structural ordering in shear flow.
In this study, we performed CGMD simulations with the aim to reveal the molecular-level friction mechanism in boundary lubrication between nanostructured steel surfaces. As lubricant molecules, polyethylene (nonpolar) and fatty acid (polar) were modeled by the coarse-grained method representing methylene (CH2) and carboxyl (COOH) groups by individual particles. The effect of the surface nanostructure was mimicked by distributing atoms producing stronger attraction with the molecular groups. The effect of alignment of the strong potentials on the friction coefficient is apparent in the case of polar molecules. In both polar and nonpolar lubricants, the nanostructure enhances critical shear stress for separation of adsorbed lubricants from the surface. These results suggest salient influence of the surface nanostructure on the friction coefficient.
To reveal the mechanism of lubrication between metal surfaces, atomic- or molecular-level investigations are required for the effect of metal-molecule interaction on boundary lubrication. Coarse-grained molecular dynamics (CGMD) is a useful and efficient simulation method to tackle such problems. Indeed, a CGMD study of shear flow of lubricant molecules between metal surfaces showed that the more molecules were adsorbed on the surfaces, the lower the friction coefficient became. Nevertheless, molecular-level mechanisms are not fully understood regarding the experimentally presented effect of the surface nanostructure on the friction coefficient or the nature of structural ordering in shear flow.
In this study, we performed CGMD simulations with the aim to reveal the molecular-level friction mechanism in boundary lubrication between nanostructured steel surfaces. As lubricant molecules, polyethylene (nonpolar) and fatty acid (polar) were modeled by the coarse-grained method representing methylene (CH2) and carboxyl (COOH) groups by individual particles. The effect of the surface nanostructure was mimicked by distributing atoms producing stronger attraction with the molecular groups. The effect of alignment of the strong potentials on the friction coefficient is apparent in the case of polar molecules. In both polar and nonpolar lubricants, the nanostructure enhances critical shear stress for separation of adsorbed lubricants from the surface. These results suggest salient influence of the surface nanostructure on the friction coefficient.