  We performed molecular dynamics simulations to study equilibrium and flow
properties of a liquid in a nano-channel with confining surfaces coated with a
layer of grafted semiflexible polymers. The coverage spans a wide range of
grafting densities from essentially isolated chains to dense brushes. The
end-grafted polymers were described by a bead spring model with an harmonic
potential to include the bond stiffness of the chains. We varied the rigidity
of the chains, from fully flexible polymers to rigid rods, in which the
configurational entropy of the chains is negligible. The brush-liquid
interaction was tuned to obtain a super-hydrophobic channel, in which the
liquid did not penetrate the polymer brush, giving rise to a Cassie-Baxter
state. Equilibrium properties such us brush height and bending energy were
measured, varying the grafting density and the stiffness of the polymers. We
studied also the characteristics of the brush-liquid interface and the
morphology of the polymers chains supporting the liquid for different bending
rigidities. Non-equilibrium simulations were performed, moving the walls of the
channel in opposite directions at constant speed, obtaining a Couette velocity
profile in the bulk liquid. The molecular degrees of freedom of the polymers
were studied as a function of the Weissenberg number. Also, the violation of
the no-slip boundary condition and the slip properties were analyzed as a
function of the shear rate, grafting density and bending stiffness. At high
grafting densities, a finite slip length independent of the shear rate or
bending constant was found, while at low grafting densities a very interesting
non-monotonic behaviour on the bending constant is observed.
