  We present Monte Carlo simulations of colloidal particles pulled into grafted
polymer layers by external fields. The insertion free energy of a single
colloid into the polymer layer is qualitatively different for surfaces with an
ordered and a disordered distribution of grafting points. Moreover, the
tendency of colloidal particles to traverse the grafting layer is strongly size
dependent. In dense colloidal suspensions, under the influence of sufficiently
strong external force, a collective instability allows the colloids to
penetrate and form internally ordered, columnar structures spanning the polymer
layer. Depending on the conditions, these colloidal clusters may be isolated or
laterally percolating. The morphology of the observed patterns can be
controlled by the external fields, which opens up new routes for the design of
thin structured films.
