Shear behavior of a confined thin film: Influence of the molecular dynamics scheme employed
Résumé
In this work, we have considered and compared two molecular dynamics schemes widely used when studying a thin fluid film confined between solid surfaces and undergoing boundary shear. In the first approach, the non-equilibrium simulations are performed on a confined fluid explicitly connected to bulk reservoirs. In the second one, non-equilibrium simulations are carried out on the confined fluid only, in which the average density is deduced from a prior simulation in the grand canonical ensemble. We have found that the apparent properties (average density and effective viscosity) of a strongly confined Lennard-Jones liquid are significantly different using one scheme or the other when the solid surfaces induce a strong structure in the whole fluid, i.e., for small separations between the solid surfaces. Furthermore, the shear velocity dependence of the friction force has been found to be as well very sensitive to the approach chosen and can be well understood in terms of the fluid structure, which can even lead to a visco-plastic behavior of the fluid in some cases. Finally, it is shown that the first scheme is the only one usable to explore the history-dependence of the friction force as observed in experiments.
Mots clés
Boundary shears
Bulk reservoirs
Confined fluids
Effective viscosity
Fluid-structures
Friction force
Grand canonical ensemble
Lennard-Jones liquids
Non-equilibrium simulations
Prior simulation
Shear behavior
Shear velocities
Solid surface
Thin fluid films Engineering controlled terms: Friction Engineering main heading: Molecular dynamics