Interface localization-delocalization transition in a symmetric polymer blend: A finite-size scaling Monte Carlo study - art. no. 021602

Using extensive Monte Carlo simulations, we study the phase diagram of a sy mmetric binary (AB) polymer blend confined into a thin film as a function o f the film thickness D. The monomer-wall interactions are short ranged and antisymmetric, i.e., the left wall attracts the A component of the mixture with the same strength as the right wall does the B component, and this giv es rise to a first order wetting transition in a semi-infinite geometry. Th e phase diagram and the crossover between different critical behaviors is e xplored. For large film thicknesses we find a first order interface localiz ation-delocalization transition, and the phase diagram comprises two critic al points, which an the finite film width analogies of the prewetting criti cal paint. Using finite-size scaling techniques we locate these critical po ints, and present evidence of a two-dimensional Ising critical behavior. Wh en we reduce the film width the two critical paints approach the symmetry a xis phi = 1/2 of the phase diagram, and for D approximate to 2R(g) we encou nter a tricritical point. For an even smaller film thickness the interface localization-delocalization transition is second order, and we find a singl e critical point at phi = 1/2. Measuring the probability distribution of th e interface position, we determine the effective interaction between the wa ll and the interface. This effective interface potential depends on the lat eral system size even away from the critical points. Its system size depend ence stems from the large but finite correlation length of capillary waves. This finding gives direct evidence of a renormalization of the interface p otential by capillary waves in the framework of a microscopic model.