Structure of grafted polymers, investigated with neutron reflectometry

Neutron reflectometry is used to investigate the structure of polymers end- grafted to an interface at high grafting densities, so-called brushes. Our system consists of polystyrene-polyethyleneoxide (PS-PEO) diblock copolymer s, irreversibly adsorbed at the air/D2O interface. At relatively low grafti ng densities the density profile of a monodisperse brush is block-like, wit h a tail region in which the density smoothly decays towards zero. At high grafting density the profile is predominantly parabolic. Bimodal brushes ar e examined for several length ratio's and mixing ratio's. At a given grafti ng density the extension of the long chains is larger in a bimodal brush th an in a monodisperse. This additional extension increases with increasing l ength and fraction of small chains. Good agreement is found between the den sity profiles obtained from analysis of the neutron reflectometry data and profiles predicted by the Scheutjens-Fleer self-consistent-field model. (C) 2000 Published by Elsevier Science B.V. All rights reserved.