Perpendicular orientation of microdomains in PS-b-PMMA thin films on the PS brushed substrates

The microdomain orientation in thin films of cylinder- and lamella-forming polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) copolymers on polystyrene (PS) brushed (or grafted) substrates was studied using scanning force microscopy (SFM) and grazing incidence small-angle X-ray scattering (GISAXS), where the grafting density (σ) of the underlying PS layers are controlled. The perpendicular orientation for cylindrical and lamellar microdomains in PS-b-PMMA films was found when the grafting density range of the PS brush was adjusted, which is presumably caused by the surface heterogeneity of the effective PS brush chains on the PS brushed substrates, rather than the balanced interfacial interactions. These results suggest that the homopolymer brushed substrates of the same chemical identity with one component of BCP may serve as a facile means to achieve a desired microdomain orientation of BCP films by controlling σ of the underlying polymer layers.