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 Tg. 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.