Assembling and organizing block copolymer nanostructures with the aid of liquid crystals*

Attaching mesogens to block copolymer backbones (BCP) can result in a rich interplay of self-assembly on multiple lengthscales, and provides new opportunities to control nanostructure development. We examine the self-assembly and directed-self assembly under magnetic fields of LC BCPs and BCP-analogous macromolecules containing mesogens. We observe a rich phase behavior, including the formation of gyroid morphologies and highly asymmetric phase diagrams, and we encounter systems with structural periodicities as small as ~6 nm. We consider the phase behavior and field alignment of a cylinder-forming system in the presence of labile mesogens that swell the LC block. The system transitions from hexagonal cylinders to FCC spheres beyond a critical mesogen concentration. Despite the isometric nature of the cubic lattice, the system aligns with the [100] axis parallel to the applied magnetic field, resulting in a degenerate, fiber-like texture. We speculate that this response may originate from symmetry breaking due to the action of the field that leads to a 2-step ordering process of the spherical microdomains. Alternatively, the response may indicate the presence of an unexpected magnetic easy axis in this cubic system.