Abstract: Liquid crystals possess structural order that is intermediate between that of fully isotropic liquids and three-dimensionally periodic solids. They are intriguing soft matter systems that display a rich collection of physico-chemical phenomena that are of fundamental interest, but that are also useful for the engineering of useful materials and devices. Here, we explore the influence of liquid crystallinity on macromolecular self-assembly (microphase separation) and on the demixing of simple binary systems (macrophase separation). 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. 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 and magnetoresponsive systems, including field-induced symmetry breaking. Finally, we explore phase separation due to thermally induced demixing in binary mixtures of mesogens with a hydrocarbon solvent. In the presence of sufficiently elastic mesophases, demixing occurs via the formation of filamentous intermediates that exhibit lower elastic free energy relative to the canonical spherical domains or droplets seen during conventional liquid-liquid phase separation. We detail the subsequent cascade of events as filaments grow and collapse into flat drops that form a ramified smectic network around which active flows are established as the phase separation proceeds.
Bio: Dr. Osuji is 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, at University of Pennsylvania. He is an Associate Editor for Macromolecules and a member of the Board of Directors of the Materials Research Society (2021-2014). 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 molecular materials, and rheology of dense, disordered systems. Prof. Osuji received his undergraduate degree in Materials Science and Engineering from Cornell followed by his Ph.D, also in Materials Science and Engineering from MIT in 2003. From 2003-2005 he was a Senior Scientist at a startup company, Surface Logix Inc., before moving to Harvard as a Postdoctoral Associate in Applied Physics (2005-2007). He was on the faculty at Yale University in the Department of Chemical and Environmental Engineering from 2007-2018 before moving to the University of Pennsylvania. Prof. Osuji is a Fellow of the American Physical Society, and a recipient of a CAREER award from the National Science Foundation (2008). 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). In 2022 he received the Prince Sultan Bin Abdulaziz International Prize for Water (PSIPW).
