Arrangement of lamellar microdomains of block copolymer confined in hemispherical cavities having two controlled interfaces

Abstract

We studied the arrangement of lamellar microdomains of polystyrene-block- poly(methyl methacrylate) copolymer (PS-b-PMMA) confined in hemispherical cavities prepared by anodic aluminum oxide template. The cavities have two controlled interfaces. One is the cavity wall grafted with three different brushes (two selective brushes made of PMMA-OH and PS-OH and one neutral brush made of PS-ran-PMMA-OH). The other is the top surface of the cavity covered with films of PMMA and PS homopolymers and PS-ran-PMMA copolymer. When the cover film was selective to one of block components, parallel lamellae were formed at the top of the cavity. On the other hand, the lamellar microdomain arrangement at the middle and bottom parts of the cavity highly depended on the nature of brushes on the cavity wall: concentric (onion-like) lamellae for a selective brush and unspecific complex structure for a neutral brush. Once parallel lamellae and concentric lamellae meet together, isolated spheres consisting of one block are formed. When the cavity wall is modified by the neutral brush and the cover layer is selective to one of the blocks, stacked lamellae are observed. However, when the cover film is neutral to both block chains, concentric lamellae or bicontinuous lamellae are formed, depending on the nature of the brushes on the cavity wall. We also performed numerical mean field calculations based on the well-established self-consistent field theory, from which we were able to reproduce the experimental results.