Hierarchical Nanostructures and Self-Assemblies in Smectic-Nematic Liquid Crystalline Diblock Copolymers

Coexistence of smectic and nematic orders in 3D curvaceous bicontineous cubic or hexagonal hierarchical structures is observed in a novel class of nanophase separated, flexible double liquid crystalline (LC) diblock copolymers of different molecular weights (MWs) but similar compositions, obtained via sequential anionic polymerization. The diblock copolymer of higher MW exhibits an exceptional order-order transition (OOT) from lamellae (Lam) to hexagonal-packed cylinder (HPC) upon nematic ordering. In contrast, the polymer with lower MW forms a thermodynamically stable, ordered gyroid structure, interwining with LC defects on nanoscale. Delicate balance of collective LC interactions and geometric frustration dictates this unique behavior, which offers a genuine way to fine-tune 2D and 3D complex structures with sub-10 nm feature sizes.