SURFACE ENRICHMENT IN A MISCIBLE POLYMER BLEND - AN EXPERIMENTAL TESTOF SELF-CONSISTENT-FIELD AND LONG-WAVELENGTH APPROXIMATION MODELS

Neutron reflectivity (NR) and low-energy forward recoil spectrometry ( LE-FRES) were used to study surface enrichment in miscible blends of d euterated polystyrene, d-PS, and poly(styrene-co-4-bromostyrene), PBr0 .049S, having a 0.049 mole fraction of 4-bromostyrene units. The d-PS component was found to segregate preferentially to the polymer blend/a ir interface, whereas no enrichment of either component was detected a t the polymer blend/silicon interface. The experimental values of the surface concentration, phi(1), and the surface excess, z, of d-PS wer e interpreted using both the theory of Schmidt and Binder (SE) (J. Phy s. II (Paris) 1985, 46, 1631) and the self-consistent field (SCF) appr oach of Genzer et al. (Phys. Rev. E 1994, 50, 2373). Although both SE and SCF models were found to be in good qualitative agreement with the experimentally measured values of phi(1) and z, we demonstrate that the latter proves to be in better quantitative agreement with the expe rimental results. Moreover, a comparison of the SE and SCF volume frac tion profiles of d-PS revealed that the SCF model described more accur ately the experimental profile. We also demonstrated that adding long- range interactions to the surface potential in the SCF model produced just minor changes in the shape of the d-PS profile near the surface.