n-Pentanol Lubrication of Silica Layers Passivated with Hydroxyl Groups Under Constant Shear Stress and Load and Isothermal Conditions

We conducted molecular dynamics simulations to study the frictional behavior of hydroxyl-passivated silica layers lubricated with n-pentanol chains under constant shear stress, constant normal load, and isothermal conditions. We analyzed the resulting single, multiple, and continuous sliding regimes for several shear stresses at a single normal load and proposed a sliding mechanism between the n-pentanol chains' methyl groups. The critical ordering of hydrogen bonds between hydroxyl groups on the surface and the lubricant is necessary to reach the stationary state, where velocity follows a logarithmic dependence on shear stress up to a critical speed of 20 nm/ns. Stationary states corresponding to pure single slip and continuous sliding behaviors showed normal speed distributions, while multiple slip behavior showed near normal and bimodal distributions. In the single slip behavior, layers show constant displacements of 0.27 A, representing half the separation of two surface hydroxyls in the sliding direction. The lubricant experienced minor volume expansions throughout the range of studied shear stresses due to an increasing layer separation at the contact surface and increasing tilting of the lubricant chains. [GRAPHICS]

Automated summary

We used molecular dynamics simulations to investigate the friction behavior of hydroxyl-passivated silica layers lubricated with n-pentanol chains. Our study focused on constant shear stress, constant normal load, and isothermal conditions. We observed different sliding regimes and proposed a sliding mechanism between the methyl groups of the n-pentanol chains. The critical ordering of hydrogen bonds between the surface hydroxyl groups and the lubricant was found to be crucial for reaching a stationary state.