Cylindrical Domains of Block Copolymers Developed via Ordering under Moving Temperature Gradient

Abstract

A zone heating method, which imposes the moving temperature-gradient (▿T) field on ordering process of various melts in general, enabled to control a macroscopic orientation of microdomain structures in block copolymer bulk. We applied the method to a polystyrene-block-polyisoprene diblock copolymer forming hexagonally packed cylindrical domains (hex−cyl) in the absence of external fields. We discovered that the method creates the following special texture of hex−cyl: (1) The texture seemingly consists of volume-filled columnar grains with the grain axis parallel to the ▿T axis (defined as the Oz axis). (2) The cylinder axis always orients perpendicular to the Oz axis with a rotational angle φ of the cylinder axis around the Oz axis being fixed within a grain but statistically varying randomly among different grains. (3) One set of the (100) plane of hex−cyl preferentially oriented perpendicular to Oz axis with a small rotational degree of freedom around the cylinder axis. We interpret that the special texture is a consequence of the surface-induced order−disorder transition of the block copolymer under the moving ▿T field.