Molecular dynamics simulations of oscillatory Couette flows with slip boundary conditions

TL;DR

This study uses molecular dynamics simulations to explore how slip boundary conditions affect oscillatory and steady Couette flows, revealing a shear rate-dependent slip length and its relation to interfacial structure.

Contribution

It demonstrates that slip length depends on local shear rate in oscillatory flows and correlates with interfacial fluid structure, extending understanding of slip behavior under dynamic conditions.

Findings

Slip length increases linearly with shear rate in steady flows.

Velocity profiles in oscillatory flows match Stokes flow with shear-dependent slip.

Friction coefficient correlates with the structure of the first fluid layer.

Abstract

The effect of interfacial slip on steady-state and time-periodic flows of monatomic liquids is investigated using non-equilibrium molecular dynamics simulations. The fluid phase is confined between atomically smooth rigid walls, and the fluid flows are induced by moving one of the walls. In steady shear flows, the slip length increases almost linearly with shear rate. We found that the velocity profiles in oscillatory flows are well described by the Stokes flow solution with the slip length that depends on the local shear rate. Interestingly, the rate dependence of the slip length obtained in steady shear flows is recovered when the slip length in oscillatory flows is plotted as a function of the local shear rate magnitude. For both types of flows, the friction coefficient at the liquid-solid interface correlates well with the structure of the first fluid layer near the solid wall.