The Department of Chemical and Biological Engineering invites you to attend student seminars by Jonathan Chan and Sumeng Hu on Thursday, June 2nd at 1:00pm in Tech M345/on Zoom.

Jonathan Chan will present a seminar titled, "Direct visualization of bottlebrush polymers in the solid state with super-resolution microscopy."

ABSTRACT: Although the behavior of single polymer chains informs our understanding of their properties, a clear image of chains that depicts their behavior within a bulk, solid state has eluded the polymers community for decades. This is surprising given the ubiquitous nature of polymeric materials. We use super-resolution optical microscopy to capture clear and convincing images of individual chains within the bulk using a model system of bottlebrush polymers. The grafted chains along these polymers cause the rigid, extended conformations characteristic to this class of materials. By changing architectural parameters of bottlebrushes, namely the grafting density and side chain length, the rigidity of the polymers is expected to change. Here, we fluorescently label the structure of bottlebrushes and image individual chains as they rest in a matrix of undyed polymer to investigate their bulk state behavior. In addition to studying the conformations of these chains, we also investigate their orientations as affected by flow-induced shear forces during spin coating. The specificity and resolution of our techniques provide a new dimension to study universally relevant materials to a degree not previously accessible.

Sumeng Hu will present a seminar titled, "Dynamic Covalent Polymer Networks and Network Composites: Sustainable Chemical Recycling of Traditionally Non-Recyclable Materials."

Conventional polymer networks and their composites cannot be melted down and recycled into new products because the long polymer chains are permanently cross-linked by fixed covalent bonds. To address this challenge, my research has focused on developing reprocessable polymer networks containing dynamic covalent cross-links that are robust at use conditions but allow for melt-state reprocessing at high temperature. Polyurethanes (PUs) are among the most widely used commodity polymers, and the vast majority of them are used in cross-linked forms. However, the efficient recycling of PUs has never been well established. In this talk, I will first introduce a study in which we use bio-based precursors and carbon dioxide as feedstocks to develop renewable polyhydroxyurethane (PHU) networks, which are a class of sustainable PU-like materials, with excellent intrinsic reprocessability. Besides addressing the recycling issue, it is important to demonstrate that properties of reprocessable polymer networks can be optimized to meet the ongoing demand for high-performance materials. We have fabricated reprocessable PHU network composites reinforced with reactive polyhedral oligomeric silsesquioxane (POSS). In comparison with neat PHU networks, the PHU-POSS network nanocomposites exhibit significantly enhanced thermal and mechanical properties, and, more importantly, these nanocomposites can be melt-reprocessed for multiple cycles at elevated temperatures with full cross-link density recovery.

Please note that we will begin serving cookies and coffee at 12:45pm. Arrive early to grab a snack and mingle!

Seminar Zoom Link: https://northwestern.zoom.us/j/94167861595