Abstract:Molecular dynamics simulations are a powerful tool to characterize liquid-solid friction. A slab configuration with periodic boundary conditions in the lateral dimensions is commonly used, where the measured friction coefficient could be affected by the finite lateral size of the simulation box. Here we show that for a very wetting liquid close to its melting temperature, strong finite size effects can persist up to large box sizes along the flow direction, typically ∼30 particle diameters. We relate the obser… Show more
“…A recent work 59 pointed out that small inhomogeneous systems, under certain conditions, tend to underestimate the solid-liquid friction. However, in this work we have not accounted for this effect, as we focussed solely on the derivation and application of the TTCF formalism under constant pressure conditions for the study of highly confined fluid systems.…”
Section: Methodology and Computation Detailsmentioning
We derive the transient-time correlation function (TTCF) expression for the computation of phase variables of inhomogenous confined atomistic fluids undergoing boundary-driven planar shear (Couette) flow at constant pressure. Using nonequilibrium molecular dynamics simulations, we then apply the TTCF formalism to the computation of the shear stress and the slip velocity for atomistic fluids at realistic low shear rates, in systems under constant pressure and constant volume. We show that, compared to direct averaging of multiple trajectories, the TTCF method dramatically improves the accuracy of the results at low shear rates, and that it is suitable to investigate the tribology and rheology of atomistically detailed confined fluids at realistic flow rates.
“…A recent work 59 pointed out that small inhomogeneous systems, under certain conditions, tend to underestimate the solid-liquid friction. However, in this work we have not accounted for this effect, as we focussed solely on the derivation and application of the TTCF formalism under constant pressure conditions for the study of highly confined fluid systems.…”
Section: Methodology and Computation Detailsmentioning
We derive the transient-time correlation function (TTCF) expression for the computation of phase variables of inhomogenous confined atomistic fluids undergoing boundary-driven planar shear (Couette) flow at constant pressure. Using nonequilibrium molecular dynamics simulations, we then apply the TTCF formalism to the computation of the shear stress and the slip velocity for atomistic fluids at realistic low shear rates, in systems under constant pressure and constant volume. We show that, compared to direct averaging of multiple trajectories, the TTCF method dramatically improves the accuracy of the results at low shear rates, and that it is suitable to investigate the tribology and rheology of atomistically detailed confined fluids at realistic flow rates.
“…The high density of the wall is due to the reduced diameter of the wall particles and corresponds to ρ w = 1 if the quantities were normalized, assuming σ w = 1. A recent work 59 pointed out…”
Section: The Journal Of Chemical Physicsmentioning
We derive the transient-time correlation function (TTCF) expression for the computation of phase variables of inhomogenous confined atomistic fluids undergoing boundary-driven planar shear (Couette) flow at constant pressure. Using nonequilibrium molecular dynamics simulations, we then apply the TTCF formalism to the computation of the shear stress and the slip velocity for atomistic fluids at realistic low shear rates, in systems under constant pressure and constant volume. We show that, compared to direct averaging of multiple trajectories, the TTCF method dramatically improves the accuracy of the results at low shear rates, and that it is suitable to investigate the tribology and rheology of atomistically detailed confined fluids at realistic flow rates.
“…Figure 1 (a) shows the MD simulation system of a quasi-1D Couette-type flow, where the basic setup is a standard one similar to our previous study. 31,32 The two parallel solid walls were fcc crystals and every pair of the nearest neighbors in the walls was bound through a harmonic potential Φ h (r) = k 2 (r − r eq ) 2 , with r being the interparticle distance, r eq = 0.277 nm, and k = 46.8 N/m. Interactions between fluid particles and between fluid and solid particles were modeled by a 12-6 LJ potential…”
In this work, we showed a calculation method of local stress tensor applicable to nonequilibrium MD systems based on the Method of Plane (MoP). From the relation between the macroscopic velocity distribution function and the microscopic molecular passage across a fixed control plane, we derived a method to calculate the basic properties of the macroscopic momentum conservation law including the density, the velocity, the momentum flux, the interaction and kinetic terms of the stress tensor defined on a surface with a finite area. Any component of the streaming velocity can be obtained on a control surface, which enables the separation of the kinetic momentum flux into the advection and stress terms in the framework of MoP.We verified the present method through the extraction of the density, velocity and stress distributions in a quasi-1D steady-state Couette flow system and in a quasi-2D steady-state system with a moving contact line. In our method, as opposed to volume average method, the density, mass and momentum fluxes are defined on a surface, which is essential to be consistent with the mass and momentum conservation laws in dynamic systems.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.