  We study the equilibrium properties and the wetting behavior of a simple
liquid on a polymer brush, with and without presence of lubricant by multibody
Dissipative Particle Dynamics simulations. The lubricant is modelled as a
polymeric liquid consisting of short chains that are chemically identical to
the brush polymers. We investigate the behavior of the brush in terms of the
grafting density and the amount of lubricant present. Regarding the wetting
behavior, we study a sessile droplet on top of the brush. The droplet consists
of non-bonded particles that form a dense phase. Our model and choice of
parameters result in the formation of a wetting ridge and in the cloaking of
the droplet by the lubricant, i.e. the lubricant chains creep up onto the
droplet and eventually cover its surface completely. Cloaking is a phenomenon
that is observed experimentally and is of integral importance to the dynamics
of sliding droplets. We quantify the cloaking in terms of its thickness, which
increases with the amount of lubricant present. The analysis reveals a
well-defined transition point where the cloaking sets in. We propose a
thermodynamic theory to explain this behavior. In addition we investigate the
dependence of the contact angles on the size of the droplet and the possible
effect of line tension. We quantify the variation of the contact angle with the
curvature of the contact line on a lubricant free brush and find a negative
value for the line tension. Finally we investigate the effect of
cloaking/lubrication on the contact angles and the wetting ridge. We find that
lubrication and cloaking reduce the contact angles by a couple of degrees. The
effect on the wetting ridge is a reduction in the extension of the brush chains
near the three phase contact line, an effect that was also observed in
experiments of droplets on crosslinked gels.
