Springs in stripes: Evaluating chiral block copolymer behavior in the lamellar morphology

N Buchanan and MJ Grant and P Padmanabhan, PHYSICAL REVIEW MATERIALS, 9, 065601 (2025).

DOI: 10.1103/PhysRevMaterials.9.065601

Chiral block copolymers exhibiting coil-helix conformations self- assemble into several novel phases, including metastable ones. The role of the helical conformations in the thermodynamics of self-assembly is an open question, where different experimental chemistries exhibit different behaviors. In this work, a tunable simulation model is utilized to capture the wide range of experimentally observed conformations. Coil-helix block copolymers containing three types of helical conformations with differing pitch and molecular aspect ratio at different values of stiffness are studied in the lamellar microstructure, chosen to minimize the effects of packing frustration. It is found that, regardless of pitch, flexible helices exhibit anisotropy greater than the coil-coil analogues, but the anisotropy does not significantly impact the domain size of the microstructure. Stiffer helices having larger anisotropy cause a dramatic increase in domain size, depending on the pitch. A larger increase in anisotropy arises for helices with larger molecular aspect ratio, which occurs in this study for molecules with smaller pitch. Within the lamellar phase, the stiff helices exhibit strong nematic ordering and show strong interdigitation, where each molecule occupies the entire region between two adjacent interfaces. Strong nematic ordering also enhances local helicity away from the interface. Together, these results suggest that the effects of chirality and stiffness can exhibit a wide range of behavior, suggesting that coil-helix polymers can be designed specifically to achieve desired characteristics.

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