Polymer brushes under shear: molecular dynamics simulations compared to experiments

Singh, M. K., Ilg, P. ORCID: https://orcid.org/0000-0002-7518-5543, Espinosa-Marzal, R. M., Kröger, M. and Spencer, N. D. (2015) Polymer brushes under shear: molecular dynamics simulations compared to experiments. Langmuir, 31 (16). pp. 4798-4805. ISSN 1520-5827 doi: 10.1021/acs.langmuir.5b00641

Abstract/Summary

Surfaces coated with polymer brushes in a good solvent are known to exhibit excellent tribological properties. We have performed coarse-grained equilibrium and nonequilibrium molecular dynamics (MD) simulations to investigate dextran polymer brushes in an aqueous environment in molecular detail. In a first step, we determined simulation parameters and units by matching experimental results for a single dextran chain. Analyzing this model when applied to a multichain system, density profiles of end-tethered polymer brushes obtained from equilibrium MD simulations compare very well with expectations based on self-consistent field theory. Simulation results were further validated against and correlated with available experimental results. The simulated compression curves (normal force as a function of surface separation) compare successfully with results obtained with a surface forces apparatus. Shear stress (friction) obtained via nonequilibrium MD is contrasted with nanoscale friction studies employing colloidal-probe lateral force microscopy. We find good agreement in the hydrodynamic regime and explain the observed leveling-off of the friction forces in the boundary regime by means of an effective polymer–wall attraction.