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Order–Order Transition between the FCC and HCP Structures in Binary Homopolymer–Block Copolymer Blends
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DOI：10.1021/acs.macromol.6c00876.png)
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Abstract
En 中文
Recently, it was discovered that block copolymers with spherical morphologies can form various complex lattices. Since then, close-packed lattices formed from soft spherical morphologies have been studied from both experimental and theoretical perspectives. In this study, the structural changes occurring in a close-packed lattice were investigated by small-angle X-ray scattering in a binary blend consisting of the polybutadiene–poly(ε-caprolactone) block copolymer and the polybutadiene homopolymer. At room temperature, an alternating crystalline–amorphous lamellar (CA-LAM) structure was formed, and nonequilibrium hexagonal cylinders (HEX) emerged after the melting of this CA-LAM structure. Upon increasing the temperature, the HEX structure was transformed into a face-centered cubic lattice (FCC) formed by soft spheres. Upon further heating, a phase transition from the FCC phase to a hexagonal close-packed (HCP) lattice occurred. When the temperature was subsequently reduced to the temperature region of the stable FCC and annealing was performed, the HCP structured converted to a FCC structure, indicating that the FCC → HCP phase transition represented a thermoreversible order–order transition. It was also found that the spheres were arranged with liquid-like packing (LLP) upon further heating above the order–disorder transition temperature (TODT), while cooling below the TODT promoted the formation of randomly stacked hexagonal close-packed (r-HCP) spheres. Additionally, the nonequilibrium structure of HEX likely led to the formation of a stable FCC structure owing to the slow phase transition. The mobility of the LLP phase was higher than that of the nonequilibrium structure at lower temperatures, resulting in the formation of r-HCP layers because of the rapid formation of an ordered phase.
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