Internal Structure of Diblock Copolymer Brushes.

Although diblock copolymer brushes (DCBs) have been studied due to their stimuli-responsive behavior, their internal structure has been unknown. We have resolved the internal structure of DCBs using neutron reflectivity and grazing incidence small-angle X-ray scattering (GISAXS). The internal brush structure of DCBs of polystyrene-$b$-poly(methyl acrylate) (PS-b-PMA) and PMA-$b$-PS depends strongly on the block sequence and the value of $\chi $N. For the thinnest films a model of two layers with an interfacial region of finite width provides a good description of the data. For dPS-b-PMA films that are thicker and of sufficiently asymmetric composition, a third layer must be included. The necessity of including a third layer is consistent with lateral ordering of some type in the center of the brush, as evidenced by correlation peaks in GISAXS data.