Rheological study of polymer flow past rough surfaces with slip boundary conditions

TL;DR

This study investigates how polymer films slip past rough surfaces using molecular dynamics and continuum simulations, revealing how surface roughness and shear influence slip behavior and polymer conformation.

Contribution

It combines molecular and continuum approaches to analyze slip phenomena on rough surfaces, highlighting the effects of surface corrugation and shear rate on slip length.

Findings

Slip length shows a local minimum at low shear rates for flat surfaces.

Effective slip length decreases with increased surface roughness.

Continuum models overestimate slip length when surface features are comparable to polymer size.

Abstract

The slip phenomena in thin polymer films confined by either flat or periodically corrugated surfaces are investigated by molecular dynamics and continuum simulations. For atomically flat surfaces and weak wall-fluid interactions, the shear rate dependence of the slip length has a distinct local minimum which is followed by a rapid increase at higher shear rates. For corrugated surfaces with wavelength larger than the radius of gyration of polymer chains, the effective slip length decays monotonically with increasing corrugation amplitude. At small amplitudes, this decay is reproduced accurately by the numerical solution of the Stokes equation with constant and rate-dependent local slip length. When the corrugation wavelength is comparable to the radius of gyration, the continuum predictions overestimate the effective slip length obtained from molecular dynamics simulations. The analysis of the conformational properties indicates that polymer chains tend to stretch in the direction of shear flow above the crests of the wavy surface.