Generalization of the Use of Random Copolymers To Control the Wetting Behavior of Block Copolymer Films

Abstract

Random copolymer brushes of poly(styrene-r-methyl methacrylate) (PS-r-PMMA) have previously been used to control the wetting behavior of poly(styrene-b-methyl methacrylate) (PS-b-PMMA) block copolymer. Here we demonstrate that the use of random copolymer may be generalized to other block copolymer systems. A series of poly(styrene-r-2-vinylpyridine-r-hydroxyethyl methacrylate) (PS-r-P2VP-r-PHEMA) random copolymers was synthesized and evaluated as brush layers to control the orientation of domains in thin films of poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) block copolymer. On nonpreferential brushes, thin films of PS-b-P2VP had a mixed orientation of domains consisting of a perpendicular orientation of lamellar domains near the copolymer−substrate interface and a parallel orientation of lamellar domains at free surface because of the lower surface energy of the PS block. The composition window of brushes that induce vertical orientation of domains near the substrate ranges from 47.8% styrene to 57.0% styrene, as determined by SEM and GISAXS measurements of films after removal of the parallel-oriented domains at surfaces (remaining film thickness ≈ 50 nm). When the PS-b-P2VP film was confined between two brushes having compositions within the above range, perpendicular-oriented lamellae that traversed the film thickness were obtained.