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

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 surface free energy, F-s, is modeled using the quadratic form suggested by Schmidt and Binder [J Phys. II (France) 46, 1631 (1985)], namely, F-s = -mu phi(1) - 0.5 g phi(1)(2), where mu and g are the surface equivalents of the bulk chemical potential and interaction energy, respectively, and phi(1) is the surface volume fraction of the surface preferred component (A). For selected values of g and the bulk volume fraction of A, phi(infinity), the volume fraction profile and A surface excess, z*, are calculated as a function of increasing mu. The first and second order wetting transitions are indicated by a discontinuity and divergence, respectively, of z* and phi(1). In our simulations, at,high values of phi(infinity) 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 phi(infinity) depending on the value of g. The latter results contrast with those of Carmesin and Noolandi [Macromolecules 22, 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)]. (C) 1997 American institute of Physics.