Symmetry Breaking and Polymer Self-Assembly in the Presence of Liquid Crystals

The presence of mesogens attached to block copolymers (BCPs), or blended with BPCs, can result in a rich interplay of self-assembly on multiple length scales, and provides new opportunities to control nanostructure development. We explore the self-assembly and directed self-assembly of liquid crystalline (LC) BCPs, block co-oligomers and BCP-analogous macromolecules containing mesogens. These systems display complex phase behavior, including the formation of highly persistent domains, gyroid morphologies and strongly asymmetric phase diagrams, and we encounter systems with structural periodicities as small as ~6 nm. The stimuli responsiveness of LC mesophases represents a useful handle to control ordering processes, and we examine this in the context of a photoresponsive system in which cis-trans isomerization can be used to stimulate rapid ordering transitions under ambient conditions. We address the phase behavior and magnetic field alignment of LC BCPs in the presence of labile mesogens. The surface anchoring of the mesogens provides control over the orientation of the BCP structures, and volumetric swelling by the labile mesogens leads to order-order transitions. We observe a transition from hexagonal cylinders to FCC spheres beyond a critical mesogen concentration. Despite the isometric nature of the cubic lattice, this system aligns with its [100] axis parallel to an applied magnetic field, resulting in a degenerate, fiber-like texture. This response originates from symmetry breaking due to the action of the field, and shares features in common with magnetic metallic systems that undergo structural phase transformations associated with magnetic ordering.