Atomistic modeling of environmental aging of epoxy resins
Author(s)
Li, Yao
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Abstract
In this work, epoxy resins were modeled using all atom representations in
nanoscale simulation boxes. Tetrafunctional epoxy and corresponding multifunctional
amine were chosen as model materials. Algorithms of constructing interconnected
network structures were invented developed to properly account for the chemical
structures and computational cost.
Monomers were generated in diamond lattice and crosslinked to model complex
epoxy multifunctional network. The initial configurations were relaxed and equilibrated
using molecular dynamics and suitable force field. Physical, thermal and mechanical
properties resulting from equilibrated simulation box are in good agreement with
experimental results.
Possible impact of chemical degradation was studied by adopting oxidation and
hydrolysis algorithms. Mechanism of degradation was based on bonds reaction
probability and chemical structures of epoxies. Both oxidation and hydrolysis were found
to decrease materials performances by reducing number of crosslinking points. Elastic
modulus of materials was directly related to crosslinking density.
Interfaces between two types of epoxies were constructed to study interactions at
interfaces. Covalent bonds linking two components play an important role in interfacial
strength. Free volume calculation helps to identify and monitor nucleation of crazes and
voids within materials. It was found voids and cracks prefer to initiate and grow at
2
interfaces and lead to failures. Additional compatibilizer layers can improve overall
composite performances by preventing void growth at interfaces.
Diffusion pattern of water in epoxy resins was studied by tracking displacement
of single molecules during certain time intervals. The characteristic of water diffusion in
epoxies was interpreted by free volume theory.
Reactive force field was introduced to study thermal degradation behavior of
epoxy resins. Number of molecules and variation of different types of covalent bonds
during heating processes were tracked and analyzed to uncover the degradation
mechanism of epoxy resins.
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Date
2012-03-29
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Text
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Dissertation