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

Abstract

Using Couette and Poiseuille flow, we extract the temperature dependence of the slip length, $δ$, from molecular dynamics simulations of a coarse-grained polymer model in contact with an attractive, corrugated surface. $δ$ is dictated by the ratio of bulk viscosity and surface mobility. At weakly attractive surfaces, a lubrication layer forms, $δ$ 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, $δ$ 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.