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

Abstract

Molecular dynamics simulations were employed to study the frictional behavior of silica layers passivated with hydroxyl groups and n-pentanol chains at constant shear stress, constant normal load, and isothermal conditions. We analyzed the shear stress conditions that produce sliding conditions under regimes of single slips, multiple slips, and continuous sliding. We also analyzed the single and multiple slips in terms of their conformations and displacements and proposed a sliding mechanism between the methyl groups of the n-pentanol chains located at the sliding surface. We studied the equilibration periods, which can reach high accelerations, prior to the continuous sliding behavior. A critical ordering of the hydrogen bonds at the silica surface is needed prior to reaching the stationary state. The velocities obtained in the stationary states follow a logarithmic dependence with the shear stresses, as previously reported for the single slip regime. Finally, we studied the conformations of the systems under the shortest and the largest shear stresses, which resulted in small changes in the lubricant volume, expanded as the shear stress increased.