Tuning Viscoelastic and Mechanical Properties in Advanced Thermosets: The Role of Stoichiometry, Surface Modification, and Hybrid Synthesis
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Cho, Jaehyun
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Abstract
This dissertation presents an integrated materials design strategy for tuning the mechanical, thermal, and viscoelastic properties of advanced thermosets. The research addresses the growing demand for high-performance, reprocessable polymers through three complementary investigations focused on covalent adaptable networks (CANs), its composite systems, and organic-inorganic hybrids development.
The first study investigates Aza-Michael chemistry based CAN, demonstrating that the stoichiometric balance between acrylate and amine functional groups is a critical parameter for controlling stress relaxation and reprocessability. Spectroscopic and mechanical analyses reveal that while systems with balanced stoichiometry maintain mechanical integrity over multiple reprocessing cycles, off-stoichiometry compositions can be engineered for faster network rearrangement at the cost of mechanical robustness.
The second part of the work introduces an interfacial engineering strategy to modulate stress relaxation by incorporating surface-modified silica nanoparticles into the CAN matrix. While amine-functionalized fillers enhanced stress relaxation, the effect was found to be highly dependent on the matrix stoichiometry rather than the alkyl chain length of the surface ligands. These findings highlight the nuanced interplay between filler-matrix interactions and network dynamics, where fillers simultaneously provide chemical pathways to accelerate bond exchange while imposing physical constraints that increase the energy barrier for relaxation.
Finally, the dissertation presents a novel organic–inorganic hybrid epoxy system using aluminum isopropoxide (AIP) as a dual-function agent that acts as both a polymerization initiator and a structural crosslinker, eliminating the need for conventional hardeners. A custom high-pressure curing method was developed to fabricate dense, homogeneous materials. Kinetic analysis confirmed an autocatalytic reaction mechanism, and an optimal AIP concentration was identified to yield superior thermal and mechanical properties.
Together, these studies illustrate a comprehensive design strategy that provides fundamental insights and practical tools for developing the next generation of reprocessable, high-performance thermosets.
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2025-07-29
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Dissertation