  We analyze the shear response of grafted polymer chains in shear flow via
coarse-grained molecular dynamics simulations. Our simulations confirm that the
shear response is dominated by the brush's outermost correlation volume, which
depends on shear rate at high Weissenberg number. The system's shear stress can
be approximated by the brush's entropic stress. The simulations further reveal
that at low Weissenberg number, the entropic shear stress of grafted chains is
independent of the Weissenberg number. Increasing the Weissenberg number leads
to Wi-dependent behavior: chains first reorient along the shear direction and
elongate at higher Wi. The entropic shear stress increases linearly with
Weissenberg number in this regime. We relate these calculations to experimental
observations on the velocity dependence of brush and hydrogel friction.
