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Polymers 2016, 8(7), 254; doi:10.3390/polym8070254

Influence of Chain Stiffness, Grafting Density and Normal Load on the Tribological and Structural Behavior of Polymer Brushes: A Nonequilibrium-Molecular-Dynamics Study

1
Laboratory for Surface Science and Technology, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland
2
School of Mathematical and Physical Sciences, University of Reading, Reading RG6 6AX, UK
3
Laboratory for Smart Interfaces in Environmental Nanotechnology, Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Champaign, IL 61801, USA
4
Polymer Physics, Department of Materials, ETH Zurich, CH–8093 Zurich, Switzerland
*
Authors to whom correspondence should be addressed.
Academic Editor: Roland G. Winkler
Received: 31 May 2016 / Revised: 24 June 2016 / Accepted: 1 July 2016 / Published: 8 July 2016
(This article belongs to the Special Issue Semiflexible Polymers)
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Abstract

We have performed coarse-grained molecular-dynamics simulations on both flexible and semiflexible multi-bead-spring model polymer brushes in the presence of explicit solvent particles, to explore their tribological and structural behaviors. The effect of stiffness and tethering density on equilibrium-brush height is seen to be well reproduced within a Flory-type theory. After discussing the equilibrium behavior of the model brushes, we first study the shearing behavior of flexible chains at different grafting densities covering brush and mushroom regimes. Next, we focus on the effect of chain stiffness on the tribological behavior of polymer brushes. The tribological properties are interpreted by means of the simultaneously recorded density profiles. We find that the friction coefficient decreases with increasing persistence length, both in velocity and separation-dependency studies, over the stiffness range explored in this work. View Full-Text
Keywords: boundary lubrication; shear; coefficient of friction; solvent quality; semiflexible polymers; planar brush; bending stiffness; FENE-chain model; polymer brushes boundary lubrication; shear; coefficient of friction; solvent quality; semiflexible polymers; planar brush; bending stiffness; FENE-chain model; polymer brushes
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Singh, M.K.; Ilg, P.; Espinosa-Marzal, R.M.; Spencer, N.D.; Kröger, M. Influence of Chain Stiffness, Grafting Density and Normal Load on the Tribological and Structural Behavior of Polymer Brushes: A Nonequilibrium-Molecular-Dynamics Study. Polymers 2016, 8, 254.

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