Static and dynamic properties of the interface between a polymer brush and a melt of identical chains

TL;DR

This study uses molecular dynamics simulations to analyze the static and dynamic behaviors of polymer brushes interfacing with a melt of identical chains under shear, revealing how grafting density influences interfacial properties.

Contribution

It provides new insights into how grafting density affects the interfacial structure and flow behavior of polymer brushes in contact with melts under shear conditions.

Findings

Interdigitation of melt into the brush varies with grafting density.

Viscosity and slip length depend on shear velocity and grafting density.

Orientation of chains is affected by shear and grafting density.

Abstract

Molecular dynamics simulations of a short-chain polymer melt between two brush-covered surfaces under shear have been performed. The end-grafted polymers which constitute the brush have the same chemical properties as the free chains in the melt and provide a soft deformable substrate. Polymer chains are described by a coarse-grained bead-spring model with Lennard-Jones interactions between the beads and a FENE potential between nearest neighbors along the backbone of the chains. The grafting density of the brush layer offers a way of controlling the behavior of the surface without altering the molecular interactions. We perform equilibrium and non-equilibrium Molecular Dynamics simulations at constant temperature and volume using the Dissipative Particle Dynamics thermostat. The equilibrium density profiles and the behavior under shear are studied as well as the interdigitation of the melt into the brush, the orientation on different length scales (bond vectors, radius of gyration, and end-to-end vector) of free and grafted chains, and velocity profiles. The viscosity and slippage at the interface are calculated as functions of grafting density and shear velocity.