Molecular Assembly and Mechanics of Functional Mesoscale Architectures

Machnicki, Catherine Elaine

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Overview

Year:: 2023
Contributor:: Machnicki, Catherine Elaine (creator); Wong, Ian (Advisor); Kim, Kyung-Suk (Advisor); Rubenstein, Brenda (Reader); McDonald, Benjamin (Reader); Brown University. Department of Chemistry (sponsor)
Genre:: theses
Subject:: Atomic force microscopy; Lithium ion batteries; 2D Materials; Aerogels; Polyurea
Extent:: 12, 193 p.

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Abstract:: Engineering new functional materials and devices requires a mechanistic understanding of their nanoscale constituents and intermolecular interactions. In this thesis, I investigate self-assembled, mesoscale-architectured materials for environmental remediation, extreme mechanics, and energy storage. First, I prepare aerogels by freeze-casting naturally derived biopolymers such as silk fibroin. These biopolymers often form mechanically weak structures that degrade in water, which limits their performance under ambient conditions. Adding 2D material fillers such as graphene oxide (GO) or transition metal carbides (e.g., MXene) reinforce these aerogels via intermolecular interactions with the polymeric binder. Freeze-casting of graphene oxide and silk fibroin results in a highly water-stable, mechanically robust aerogel, not observed with silk-only or MXene and silk aerogels. These multicomponent aerogels can be utilized for environmental sensing, thermal insulation, and electrical conductivity. Second, I elucidate molecular-level deformation and failure mechanisms, i.e., clustering, dissociation, and reorganization of hard-phase nanostructures (HPNs) in synthetic polyurea. The mechanisms were revealed by an in-situ AFM probe for nano-phase morphology evolution under incremental straining followed by stress relaxation and mesoscale coarse-grain molecular dynamics (CG-MD) simulations. The dynamic-hydrogen-bond dissociation and load deformation sharing characteristics of the HPNs are intrinsic to the dynamic-toughening mechanism of polyurea. The morphological clustering of HPNs is observed to be an extrinsic toughening mechanism of void-growth initiation and ductility through void coalescence. These results bridge the molecular-structural design of copolymers to the function of dynamic strengthening and toughening under extreme loading. Finally, I evaluated two in-situ methodologies to detect failure modes under fast charging in architectured graphite anodes in lithium-ion batteries. I adapted a multi-beam optical stress sensor (MOSS) to monitor the stress evolution during lithium intercalation under fast charging. Next, we developed an in-situ optical imaging assembly to observe the graphite anode surface chemistry. Analysis from each method gave insight into the intercalation behavior for architectured graphite anodes, which can help elucidate mechanisms of failure. Overall, this thesis establishes design rules for interacting molecular building blocks for enhanced control of material structure and performance.
Notes:: Thesis (Ph. D.)--Brown University, 2023

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Citation

Machnicki, Catherine Elaine, "Molecular Assembly and Mechanics of Functional Mesoscale Architectures" (2023). Chemistry Theses and Dissertations. Brown Digital Repository. Brown University Library. https://repository.library.brown.edu/studio/item/bdr:rgf94yjn/

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Chemistry Theses and Dissertations

Theses and Dissertations for the Chemistry department.
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