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 w here polymers A and B have equal numbers of segments, N. The surface f ree energy, F-s, is modeled using the quadratic form suggested by Schm idt and Binder [J Phys. II (France) 46, 1631 (1985)], namely, F-s = -m u 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 com ponent (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 o rder wetting transitions are indicated by a discontinuity and divergen ce, 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 tran sitions are observed for low values of phi(infinity) depending on the value of g. The latter results contrast with those of Carmesin and Noo landi [Macromolecules 22, 1689 (1989)], who found that only first orde r wetting transitions are possible polymer mixtures. However, our resu lts are in agreement with recent Monte Carlo simulations carried out b y Wang and Binder [J. Chem. Phys. 94, 8537 (1991)] and Pereira and Wan g [J. Chem. Phys. 104, 5294 (1996)]. (C) 1997 American institute of Ph ysics.