Interfacial Segment Density Profiles of End-Anchored Polymers in a Melt

The segment density profile of end-functionalized deuterated polystyrene (EF-dPS) polymers anchored in a surrounding melt of hydrogenated polystyrene (hPS) to an interface with silicon was determined by neutron reflectometry. Thin films of mixtures with various volume fractions of the EF-dPS and hPS were spun cast from toluene solutions onto the silicon. These films as cast were uniform as a function of depth. After heating to 184 °C for approximately 1 day to allow equilibrium segregation to be achieved in the films, neutron reflection measurements were performed. The EF-dPS segment density profiles ϕ(z) needed to fit the reflectivity data showed a high ϕ at the silicon interface which increased to a maximum approximately 10 nm away from the interface and then fell monotonically to the bulk segment density ϕ_∞. The interface excess determined by integration of these profiles was in excellent agreement with that directly determined by forward recoil spectrometry on the same samples. The form of the profiles is consistent with the predictions of a self-consistent mean field theory if, in addition to a large attachment free energy of the end group to the silicon, there is a weak preferential attraction of the silicon for the more polarizable hPS segments relative to the less polarizable dPS segments.