  There is ample evidence that polymer brushes reduce friction between
surfaces. Several industrial applications take advantage of this fact, such as
those in plastic bag production, where the brushes act as slip agents; however,
the complex mechanisms that give rise to such reduction of friction are not yet
fully understood. In this work we report coarse grained, dissipative particle
dynamics simulations carried out for surfaces functionalized with erukamide
brushes, a polymer commonly used in the plastics industry as a slip agent
between surfaces. We calculate their rheological properties, such as the
coefficient of friction (COF) and the viscosity, {\eta}, as functions of the
number of chains grafted on the surfaces under the influence of stationary,
Couette flow. Moreover, we consider also the case when a fraction of the
erukamide chains is not adsorbed and moves freely between the surfaces. We show
that the COF reaches an equilibrium value of about 0.29 in these two cases, in
agreement with experimental results. On other hand, the viscosity grows
monotonically, as a result of the increasing collisions when the erukamide
content is increased. The force between brushes is found to be in agreement
with predictions from scaling theories. We find that the addition to free
chains helps stabilize the film formed by the brushes and the solvent, as
others have found experimentally. The mechanisms that give rise to these
phenomena are studied in detail.
