  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.
