Collective ordering of colloids in grafted polymer layers

Abstract

We present Monte Carlo simulations of colloidal particles pulled into grafted polymer layers by an external force. The insertion free energy for penetration of a single colloid into a polymer layer is qualitatively different for surfaces with an ordered and a disordered distribution of grafting points and 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 forces, colloids penetrate and form internally ordered, columnar structures spanning the polymer layer. The competition between the tendency for macro-phase separation of colloids and polymers and the elastic-like penalty for deforming the grafted layer results in the micro-phase separation, i.e. finite colloidal clusters characterized by a well-defined length scale. Depending on the conditions, these clusters are 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.