Soft-materials such as block copolymers, surfactant and liquid crystals exhibit variety of ordered microstructures. Among them, the phase diagrams of diblock copolymers have been extensively investigated both experimentally and theoretically. Matsen and Shick[1] calculated the phase diagram of diblock copolymer melts by using self-consistent field theory (SCFT) and predicted that the phase diagram contains four types of structures: sphere packed in body-center-cubic, hexagonally-packed cylinders, lamellar and double-gyroid network. Khandpur et al.
Morphological changes related to deformation of styrene-butadiene-styrene block copolymers with a cylindrical microdomain structure have been studied by small-angle X-ray scattering. The behavior of originally isotropic, solution-cast samples has been compared with the deformation and related structural changes of samples with original macroscopically oriented morphology. The structure related to various stages of deformation has been determined from SAXS patterns by considering separately changes in the single-particle scattering and changes in the lattice factor, both of which influence the scattering patterns. The early and intermediate stages of deformation of the triblock copolymer are controlled by its morphology, while at large extensions the deformation and resulting structure are determined by molecular orientation in the polybutadiene phase.
Real-time and in-situ small-angle X-ray scattering (SAXS) studies were conducted on polystyrene-block-poly (ethylene-alt-propylene) copolymer films having alternating lamellar microdomains. SAXS was detected with a 2D detector from the film specimens subjected to a large-amplitude oscillatory shear deformation with a sawtooth type strain y (-0.5 < y < 0.5) at frequency / = 0.0149 or 1 Hz and at temperature T = 105 or 130 °C. The specimens initially had a uniaxial orientation with the lamellar normal 1 preferentially oriented parallel to the film normal (OZ axis). The shear deformation at low temperature and low frequency (f = 0.0149 Hz, T = 105 °C) or that at high temperature and high frequency (f = 1 Hz, T-130 °C), with the displacement vector parallel to the OY axis and the shear gradient axis parallel to the OZ axis, gave a biaxial orientation with 1 preferentially oriented along either the OZ or OY axis, the former being dominant to the latter. On the other hand, the shear deformation at high temperature and low frequency (f = 0.0149 Hz, T = 130 °C) gave an improved uniaxial orientation of 1 with respect to the OZ axis. A preferred orientation of 1 along the OX axis, the neutral axis, was not detected in any case. The two deformations which gave the biaxial orientation involved about the same shear stress level, but this stress level was much higher than that involved in the deformation giving rise to the improved uniaxial orientation.
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.
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