Investigation of Frank-Kasper phases in High Compositionally and Conformationally Asymmetric Block Copolymers
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The quasicrystalline structures disclosed in diblock copolymers (BCPs) have fascinated new insight for designing soft materials endowed with unique structural properties. Recently, Bates and coworkers discovered various of Frank-Kasper (FK) phases such as Sigma (σ), A15, C14 and C15 phases. Based on the self-consistent field theory, the stability window of σ phase between hexagonally packed cylinder (HEX) and body-centered cubic (BCC) phases becomes larger as the value of conformational asymmetry (ε) of BCPs increases. In this study, we designed a high-ε, high‒χ and low‒Tg BCPs consisting of the soft siloxane in major and rigid fluorine-containing acrylate to simplify the rapid equilibrium of nano-structures at lower temperatures. Evaluated value of ε was about 2.20 which is higher than other BCPs reported in the literature. As a result, between HEX and BCC phases under a disordered state, the FK σ and C14 phases were identified by the small-angle X-ray scattering analysis.