Stabilizing Multi-Stranded Helical Supercylinders via Synergistic Effect of A- and C-Block Bidispersity in Frustrated ABC/ABC Binary Blends

Abstract Helical supercylindrical structures are one type of unique morphologies formed by “frustrated” linear ABC triblock copolymers, which exhibit more intricate geometrical features than straight cylinders. Their stabilization mechanism, especially the feasibility of stabilizing multi-stranded helices (such as quadruple helices) over broad parameter spaces, remains to be further elucidated. Using self-consistent field theory (SCFT), this work investigates how A- and C-block length bidispersity regulates the stability of hierarchical supercylindrical structures in the frustrated ABC/ABC linear triblock copolymer binary blends. The calculated phase diagrams reveal the distinct roles of A- and C-block bidispersity in regulating hierarchical supercylindrical phases. Introducing A-block bidispersity enhances the overall relative stability of hierarchical supercylinders and sequentially stabilizes the hierarchical supercylindrical phases H3C, C4C, H4C, and C6C. On this basis, C-block bidispersity operates through a morphology-selective mechanism by preferentially stabilizing helical supercylindrical phases with more severe C-block stretching nonuniformity within the matrix, thereby substantially expanding the phase regions of H3C and H4C. Our work not only deepens the understanding of the mechanisms governing the stability of helical supercylindrical structures but also offers a molecular design strategy for the experimental fabrication of multi-stranded helical supercylindrical structures, especially quadruple helices.