Neutron Reflectivity Study of Free-End Distribution in Polymer Brushes

In this study, the free-end distribution of a polystyrene self-assembled brush in good solvent (toluene-d) is directly probed by use of neutron reflectometry. This is accomplished by the selective deuterium enrichment of polystyrene chains so that all but the last 16% of the monomers of each chain are contrast-matched to the solvent. Thus, only these unlabeled terminal monomers are effectively visible to the neutrons. The analysis of the experimental results supports the picture that free ends are not localized at the brush height, but are distributed throughout the brush in agreement with previous theoretical and simulation studies. Detailed comparison is made between the experimentally determined free-end profiles and those predicted by self-consistent Field theoretical and simulation models.