CBE Seminar: Polymer Self-assembly in the Presence of Liquid Crystals

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Abstract: 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. This talk explores the self-assembly and directed self-assembly of a variety of mesophase forming systems – liquid crystalline (LC) BCPs, block co-oligomers and BCP-analogous macromolecules containing mesogens. These systems display 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. The stimuli responsiveness of LC mesophases represents a useful handle via which 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. In particular, 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.

Bio: Chinedum Osuji received his doctorate in materials science and engineering from MIT in 2003, for studies of structure-property relationships and self-assembly of liquid crystalline block copolymers with Edwin L. Thomas. From 2003-2005, he was a senior scientist at Surface Logix Inc. where he worked on soft lithography, and from 2005-2007 was a postdoctoral associate in applied physics with David A. Weitz at Harvard University where he studied shear-induced structure and dynamics of colloidal gels. From 2007-2018, he was on the faculty at Yale University in the Department of Chemical and Environmental Engineering. In 2018 he joined the University of Pennsylvania where he is currently the Eduardo D. Glandt Presidential Professor and Chair in the Department of Chemical and Biomolecular Engineering, and a secondary member of the faculty in materials science and engineering. Osuji is an associate editor for Macromolecules and serves on editorial advisory boards for Physical Review Materials, Journal of Materials Chemistry and ACS Polymers Au. He leads an experimental research group focused on structure and dynamics of soft materials and complex fluids. Topics of interest include structure-property relationships in ordered soft materials, directed self-assembly of block copolymers and other soft mesophases or molecular materials, and rheology and slow dynamics of disordered systems.

Osuji is a fellow of the American Physical Society and a recipient of a CAREER award from the National Science Foundation (2008) and the 2010 Arthur Greer award of Yale College. He received an Office of Naval Research's Young Investigator award and a 3M Nontenured Faculty award in 2012. He is the recipient of the Dillon Medal of the American Physical Society (2015), the Hendrick C. Van Ness Award (2019), and the Nano Research Young Investigator Award (2019).

Host: Assistant Professor Quinton Smith