Surface Segregation of Low Surface Energy Polymeric Dangling Chains in a Cross-Linked Polymer Network Investigated by a Combined Experimental-Simulation Approach

The surface properties of polymeric materials are generally determined by the chemical groups present at their surface. For low surface energy polymeric films the preferential location of the low surface energy chemical groups at the surface is crucial for the low-adhesion properties which are of high interest for various engineering fields. Controlling the surface segregation of such chemical groups would allow maintaining the materials properties at high performance level all through its service lifetime. In this work we used a combined experimental simulation approach to study the surface segregation and the bulk distribution of low surface energy polymeric dangling chains, chemically bonded to a cross-linked poly(urethane) network. The surface properties of the cross-linked polymeric films, prepared with different experimental parameters, were investigated by contact angle (CA) measurements and X-ray photoelectron spectroscopy (XPS). A dissipative particle dynamics (DPD) method was used to model the distribution of the low surface energy dangling chains, at the surface and in the bulk of the cross linked systems, equivalent to the ones prepared experimentally. The combined results show with excellent agreement the segregation of the low surface energy polymeric dangling chains toward the air polymer interface. The influence of different experimental parameters, such as fluorine concentration and dangling chains molecular mobility, on the surface segregation is discussed. DPD simulations revealed further details of the polymeric films structure: the formation of a depletion zone beneath the top surface and the presence of highly dynamic clusters of the polymeric dangling chains in the bulk of the network, but not at its surface.