Article pubs.acs.org/Macromolecules
Control of Air-Interface-Induced Perpendicular Nanocylinder Orientation in Liquid Crystal Block Copolymer Films by a SurfaceCovering Method Motonori Komura,*,†,‡ Atsushi Yoshitake,‡ Hideaki Komiyama,‡ and Tomokazu Iyoda‡ †
Department of Electrical and Electronics Engineering, National Institute of Technology, Numazu College, 3600 Ooka, Numazu, Shizuoka 410-8501, Japan ‡ Division of Integrated Molecular Engineering, Chemical Resources Laboratory, Tokyo Institute of Technology, 4259-R1-25 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8503, Japan S Supporting Information *
ABSTRACT: A liquid crystalline block copolymer, composed of poly(ethylene oxide) (PEO) and polymethacrylate (PMA)bearing azobenzene (Az) mesogen side chains, uniquely forms perpendicularly oriented PEO cylinders in a film on various substrates, independent of the substrate surface energy. In this paper, it is revealed that the perpendicular cylinders are formed at the air interface of the block copolymer film, as the perpendicular cylinders and liquid crystal structures were observed only in the vicinity of the air interface for a block copolymer film annealed for a short period of 5 s. On the basis of this mechanism of air-interface-induced perpendicular cylinder formation, we developed a surface covering method to prevent the perpendicular cylinder formation and instead induce parallel cylinder formation. Moreover, uniaxial cylinder films were fabricated by a combination of the surface covering and substrate rubbing methods. The surface covering layer for controlling cylinder orientation can be removed to utilize the block copolymer film for templating.
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INTRODUCTION
structures. These include microphase-separated nanostructures and crystalline or liquid crystalline structures. We report on a designed amphiphilic liquid crystalline block copolymer, PEO-b-PMA(Az), consisting of a hydrophilic poly(ethylene oxide) (PEO), and a hydrophobic polymethacrylate with azobenzene mesogen side chains (PMA(Az)). This block copolymer forms a highly ordered microphase-separated film with perpendicularly oriented cylindrical PEO domains surrounded by the PMA(Az) matrix having a smectic liquid crystalline phase.7 The microphase-separated film with the hydrophilic PEO cylinders can be easily applied to numerous block copolymer templating processes due to its amphiphilic properties.8 This block copolymer displays an extremely wide PEO cylinder window (0.083 < PEO volume fraction
