Temperature dependence of the slip length in polymer melts at attractive surfaces

TL;DR

This study investigates how the slip length of polymer melts at attractive surfaces varies with temperature using molecular dynamics simulations, revealing complex behaviors near the glass transition and the influence of surface attraction strength.

Contribution

It provides a detailed analysis of the temperature dependence of slip length in polymer melts at attractive surfaces, supported by a schematic model that generalizes the findings.

Findings

Large slip lengths increase upon cooling at weakly attractive surfaces.

Near the glass transition, slip lengths become very large.

Strongly attractive surfaces lead to small slip lengths and breakdown of Navier-slip condition.

Abstract

Using Couette and Poiseuille flow, we extract the temperature dependence of the slip length, $\delta$, from molecular dynamics simulations of a coarse-grained polymer model in contact with an attractive, corrugated surface. $\delta$ is dictated by the ratio of bulk viscosity and surface mobility. At weakly attractive surfaces, a lubrication layer forms, $\delta$ is large and increases upon cooling. Close to the glass transition temperature, $T_ g$, very large slip lengths are observed. At a more attractive surface, a``stick y surface layer" is build up, which gives rise to a small slip length. Upon cool ing, $\delta$ decreases at high temperatures, passes through a minimum and grows upon approaching $T_g$. At strongly attractive surfaces, the Navier-slip condit ion fails to describe Couette and Poiseuille flow simultaneously. The simulation results are corroborated by a schematic, two-layer model suggesting that the ob servations do not depend on the details of the computational model.