Wetting and capillary condensation in symmetric polymer blends: A comparison between Monte Carlo simulations and self-consistent field calculations

We present a quantitative comparison between extensive Monte Carlo simulations and self-consistent field calculations on the phase diagram and wetting behavior of a symmetric, binary (AB) polymer blend confined into a film. The nat walls attract one component via a short-range interaction. The repulsion between monomers of different types leads to an upper critical solution point in the bulk. The critical point of the confined blend is shifted to lower temperatures and higher concentrations of the component with the lower surface free energy. The binodals close to the critical point are flattened compared to the bulk and exhibit a convex curvature at intermediate temperatures-a signature of the wetting transition in the semiinfinite system. We present detailed profiles of the two coexisting phases in the film and estimate the line tension between the laterally coexisting phases. Using the dependence of the thickness of the wetting layers and the shift of the chemical potential on the film width, we determine the effective interaction range between the wall and the AB interface. Investigating the spectrum of capillary fluctuation of the interface bound to the wall, we find evidence for a position dependence of the interfacial tension. This goes along with a distortion of the interfacial profile from its bulk shape. Using an extended ensemble in which the monomer-wall interaction is a stochastic variable, we accurately measure the difference between the surface energies of the components, and determine the location of the wetting transition via the Young equation. The Flory-Huggins parameter at which the strong first-order wetting transition occurs is independent of chain length and grows quadratically with the integrated wall-monomer interaction strength. We estimate the location of the prewetting line. The prewetting manifests itself in a triple point in the phase diagram of very thick films and causes spinodal dewetting of ultrathin layers slightly above the wetting transition. We investigate the early stage of dewetting via dynamic Monte Carlo simulations. We compare our findings to phenomenological descriptions and recent experiments.