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CBE Doctoral Dissertation Defense: “A molecular understanding of the structure-property relationships of model end-linked polymer networks” (Han Zhang)
February 4 at 11:00 AM - 1:00 PM
Abstract:
Polymer networks, including thermoplastics, thermosets, elastomers and gels, are among the most versatile and widely utilized polymeric materials, with applications spanning drug delivery systems, membranes and implantable devices. A comprehensive understanding of the intricate relationship between the macroscopic properties and the structure and topology of polymer networks is crucial for advancing their utilization and facilitating the design of new materials. Molecular simulations have proven invaluable in exploring the structure-property relationships across various material systems. However, compared to other polymeric systems, such as polymer melts and glasses, polymer networks have received comparatively less attention in molecular simulation studies. A primary challenge lies in the inherent inhomogeneities of polymer networks, such as loop defects and dangling ends. Nevertheless, many fundamental theories about polymer networks are based on idealized network models assuming homogeneous and defect-free structures. The understanding of polymer networks from a molecular perspective has remained limited, as methods for construct models that accurately reflect real polymer network topologies have only recently begun to emerge.
This dissertation presents a computational framework that integrates molecular dynamics simulations, Monte Carlo simulations and network analysis to explore the structure-property relationships in model end-linked polymer networks containing topological defects. We demonstrate that constructing networks from engineered tapered copolymers significantly expands the composition range in which co-continuous morphologies form. These co-continuous morphologies exhibit great potential to combine typically incompatible material properties within a single sample, unlocking exciting opportunities for advanced materials design. Additionally, we investigate the elastic properties of these networks, providing valuable physical insights into how these properties are influenced by the key structural parameters of the networks, including polymer mole fractions, chain lengths and solvent quality.
Advanced computational tools are also employed to investigate the fracture process of end-linked polymer networks from a molecular perspective. Network analysis proves to be a simple yet powerful approach for identifying potential failure locations within polymer networks based solely on their initial undeformed configurations. Furthermore, by leveraging molecular simulations, we deliver a quantitatively refined, molecular-level understanding of the fracture process, tracking energy storage and dissipation at the bond, chain, generation and tree levels within the networks. These findings offer a molecular-level perspective on the influence of structure parameters and topological defects in the networks, providing valuable insights for the mechanism behind the failure process and the inverse design strategies of network materials with tailored properties.
Meeting ID: 966 7815 7284
Passcode: 809660
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Han Zhang
CBE PhD Candidate
Thesis Advisor: Robert A. Riggleman (CBE)
Committee Members: Russell J. Composto (MSE, BE, CBE), John C. Crocker (CBE), Daeyeon Lee (CBE)