Slip boundary conditions for shear flow of polymer melts past atomically flat surfaces

TL;DR

This study uses molecular dynamics simulations to explore how slip length varies with shear rate and fluid density in polymer melts near atomically flat surfaces, revealing complex dependencies and interfacial friction behaviors.

Contribution

It provides new insights into the shear rate and density dependence of slip length and interfacial friction in polymer melts at atomically smooth surfaces.

Findings

Slip length exhibits a local minimum and rapid growth at high shear rates.

The friction coefficient transitions from constant to power-law decay with slip velocity.

Interfacial friction is influenced by surface structure factor and contact density.

Abstract

Molecular dynamics simulations are carried out to investigate the dynamic behavior of the slip length in thin polymer films confined between atomically smooth thermal surfaces. For weak wall-fluid interactions, the shear rate dependence of the slip length acquires a distinct local minimum followed by a rapid growth at higher shear rates. With increasing fluid density, the position of the local minimum is shifted to lower shear rates. We found that the ratio of the shear viscosity to the slip length, which defines the friction coefficient at the liquid/solid interface, undergoes a transition from a nearly constant value to the power law decay as a function of the slip velocity. In a wide range of shear rates and fluid densities, the friction coefficient is determined by the product of the value of surface induced peak in the structure factor and the contact density of the first fluid layer near the solid wall.