(613a) Block Copolymer 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. Here, we examine the self-assembly and directed self-assembly of liquid crystalline (LC) BCPs, block co-oligomers and BCP-analogous macromolecules containing mesogens. We observe a rich 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. We consider the phase behavior and magnetic field alignment of LC BCPs in the presence of labile mesogens that selectively sequester with the LC block. At low concentrations in thin films, the labile mesogens induce a transition from parallel to perpendicular morphologies, for both lamellae and cylinder-forming systems. This display is rooted in homeotropic anchoring of the labile mesogen at the free air-surface of the film, and is robust against a variety of substrates. In bulk cylinder-forming samples, we observe a transition 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 an 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.