Rate-dependent slip boundary conditions for simple fluids

TL;DR

This study uses molecular dynamics simulations to explore how slip length in simple fluids depends on shear rate and wall-fluid interactions, revealing a nonlinear to linear transition influenced by surface structure and temperature.

Contribution

It introduces a new formula linking slip length to in-plane structure factor, contact density, and temperature, valid across various shear rates and interaction strengths.

Findings

Slip length increases nonlinearly at weak interactions

Transition to linear rate dependence with stronger interactions

A universal formula accurately predicts slip behavior

Abstract

The dynamic behavior of the slip length in a fluid flow confined between atomically smooth surfaces is investigated using molecular dynamics simulations. At weak wall-fluid interactions, the slip length increases nonlinearly with the shear rate provided that the liquid/solid interface forms incommensurable structures. A gradual transition to the linear rate-dependence is observed upon increasing the wall-fluid interaction. We found that the slip length can be well described by a function of a single variable that in turn depends on the in-plane structure factor, contact density and temperature of the first fluid layer near the solid wall. Extensive simulations show that this formula is valid in a wide range of shear rates and wall-fluid interactions.