A self-consistent field study of the wetting transition in binary polymer blends

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Abstract
A self-consistent field approach is used to investigate the partial to complete wetting transition for an A:B polymer blend at coexistence where polymers A and B have equal numbers of segments, N. The surfacefree energy, F s , is modeled using the quadratic form suggested by Schmidt and Binder [J. Phys. II (France) 46, 1631 (1985)], namely, F s =−μφ 1 −0.5gφ 1 2 , where μ and g are the surface equivalents of the bulk chemical potential and interaction energy, respectively, and φ 1 is the surface volume fraction of the surface preferred component (A). For selected values of g and the bulk volume fraction of A, φ ∞ , the volume fraction profile and A surface excess, z *, are calculated as a function of increasing μ. The first and second order wetting transitions are indicated by a discontinuity and divergence, respectively, of z * and φ 1 . In our simulations, at high values of φ ∞ only first order transitions are detected for both N=100 and N=1000. However, both first and second order wetting transitions are observed for low values of φ ∞ depending on the value of g. The latter results contrast with those of Carmesin and Noolandi [Macromolecules22, 1689 (1989)], who found that only first order wetting transitions are possible polymer mixtures. However, our results are in agreement with recent Monte Carlo simulations carried out by Wang and Binder [J. Chem. Phys. 94, 8537 (1991)] and Pereira and Wang [J. Chem. Phys. 104, 5294 (1996)].