Roles of mesh size, segmental dynamic, glass transition temperature and molecular structure on penetrant diffusion in dense vitrimers
Huang, Junrou
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https://hdl.handle.net/2142/124475
Description
Title
Roles of mesh size, segmental dynamic, glass transition temperature and molecular structure on penetrant diffusion in dense vitrimers
Author(s)
Huang, Junrou
Issue Date
2024-02-20
Director of Research (if dissertation) or Advisor (if thesis)
Evans, Christopher M
Braun, Paul V
Doctoral Committee Chair(s)
Braun, Paul V
Committee Member(s)
Moore, Jefferey S
Silverman, Scott K
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Diffusion
Vitrimer
Segmental dynamic
Mesh size
Abstract
Vitrimer, which is crosslinked by associative dynamic bond, can flow like thermoplastic under pressure or heat via bond exchange reaction, while maintain its crosslink density like thermoset. There are several potential benefits of bond exchange event that haven’t been explored. For examples, bond exchange could change the nanoscale structure inside the polymer network, which can be used as one way to control the transport properties. Understanding small molecule penetrant diffusion in polymer network is important for developing highly-efficient and selective membranes. The diffusion process is complicated, influenced by multiple factors such as polymer structure, temperature, segmental motion and interaction between penetrant and polymer. This thesis will detail our effort on understanding how dynamic bond affects the diffusion process in polymer.
Project I aims to study how a fluorescent molecule, BTBP, diffuses in n-butyl acrylate network with dynamic boronic ester crosslinks. Two different boronic ester crosslinks with widely varying bond exchange rates were utilized to study the effect of exchange kinetics on penetrant diffusion. Probe diffusion of a large anisotropic fluorescent dye molecule was investigated by fluorescence recovery after photobleaching (FRAP). The diffusion coefficients of the dye were normalized by either the mesh size or Tg/T, and in both cases diffusion is enhanced in the dynamic networks. Faster bond exchange in the network leads to faster diffusion in vitrimers.
In project II, we investigated the selective diffusion of two different dyes by reactive diffusion. These two penetrants have similar structure, but one of them could participate in reversible dynamic bonding with the dynamic crosslinks and the other could not. Our results show that dynamic crosslinks can slow down penetrant diffusion and provide a route towards selective transport in polymer membranes.
In project III, we studied the penetrant diffusion in controlled radical polymerized (CRP) and free radical polymerized (FRP) network. The choice of polymerization method do not alter Tg, but affect the modulus and crossover time. The diffusion coefficients of CRP and FRP network are similar after normalization by Tg or volumetric crosslink density.
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