{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/125569"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/125569","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Structural relaxation and penetrant diffusion in polymer networks","abstract":"Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2025-02-04 without embargo terms","abstract_html":"Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2025-02-04 without embargo terms","abstract_has_math":false,"creators":["Lin, Tsai-Wei"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Chemical Engineering","degree_department":null,"school":null,"contributors":["Sing, Charles E","Schweizer, Kenneth S","Evans, Christopher M","Kuenstler, Alexa S"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2024,"date_issued":"2024-07-09","date_published":"2024-07-09","updated_at":"2026-07-22T22:25:02Z","subjects":["Penetrant Diffusion","Crosslinked Polymer Networks","Glass Transition","Alpha Relaxation Time","Molecular Dynamics","Membrane Separation"],"languages":["en","eng"],"rights":["Copyright 2024 Tsai-Wei Lin"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/2142/125569","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Sing, Charles E","Schweizer, Kenneth S","Evans, Christopher M","Kuenstler, Alexa S"]},{"key":"dc:creator","label":"Author","values":["Lin, Tsai-Wei"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2024-07-09","2024-08"]},{"key":"dc:type","label":"Dc Type","values":["text","Thesis"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Chemical Engineering"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Penetrant Diffusion","Crosslinked Polymer Networks","Glass Transition","Alpha Relaxation Time","Molecular Dynamics","Membrane Separation"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en","eng"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright 2024 Tsai-Wei Lin"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://hdl.handle.net/2142/125569"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2025-02-04 without embargo terms","The student, Tsai-Wei Lin, accepted the attached license on 2024-07-05 at 10:44.","The student, Tsai-Wei Lin, submitted this Dissertation for approval on 2024-07-05 at 11:11.","This Dissertation was approved for publication on 2024-07-09 at 13:30.","DSpace SAF Submission Ingestion Package generated from Vireo submission #20954 on 2025-02-04 at 21:04:15","Controlling the permeation of atomic, molecular, and nanoparticle “penetrants” through dense polymeric media (liquid, glass, crosslinked permanent or dynamic rubber network, thermoset) is a crucial scientific problem broadly relevant in materials, biological chemistry, and energy sciences. In particular, understanding how the many physicochemical factors (e.g., size, shape, and chemistry) and thermodynamic state control penetrant activated mass transport is critical for membrane separations, which serve as promising alternatives to distillation or extraction for chemical separations. A remaining challenge for membrane design is the trade-off between permeability and selectivity described by an empirical upper bound of membrane performance, which the scientific community has been thriving to shift higher through structure/property optimization of membranes. Therefore, we are motivated to explore a new paradigm of using highly-crosslinked networks near glass transition temperature Tg for the selective transport of small molecules. Polymer networks hold promise in membrane separation because dramatic differences in molecular diffusion can result from subtle changes in the network structure. We constructed a coarse-grained molecular dynamics simulation model that reflects the specific polymer chemistry of the network studied, along with experiment and theory done by collaborators, to understand the role that crosslinking has in governing the structural relaxation and the transport of penetrants in polymer networks. We observed a very large increase in segmental relaxation time and glass transition temperature Tg as a result of tight crosslinking and provided a mechanistic microscopic understanding of the observations by showing that structural relaxation involves a coupled local cage and nonlocal collective physics, with the latter becoming more dominant upon cooling. Our investigation of penetrant diffusion reveals that permanent crosslinking can regulate penetrant transport through (1) the near-Tg coupling between penetrant hopping and the structural relaxation of polymer networks (2) the confining mesh that obstructs penetrant motion. We found that the main effect of permanent crosslinking is to slow down polymer structural relaxation and greatly suppress the elementary penetrant hopping event, while signatures of mesh confinement, though of secondary importance, are observed at certain conditions depending on penetrant size and thermodynamic state. The good agreement between experiment, simulation, and theory demonstrated size ratio (penetrant diameter to Kuhn length) as a key variable determining penetrant diffusivity, though the role of chemistry-specific effects (e.g, shape, penetrant-polymer interaction) are non-negligible, as shown in simulation and theory. Finally, we study the bond exchange dynamics and structural relaxation in associative dynamics covalent network (i.e., vitrimers) over wide ranges of crosslink densities fcross, temperatures T, and bond exchange rate. Simulations unravel the intricate interaction between these two dynamic processes and reveal that only when the bond exchange time scale is comparable to Kuhn segmental alpha time will the dynamic crosslinking show noticeable acceleration of segmental relaxation and change in Tg. Overall, we have developed models to connect experimental findings and theoretical predictions for specific polymer networks. These models elucidate the effect of crosslinking on structural relaxation in both permanent and dynamic polymer networks. By combining simulation, experiment, and theory, we identify the mechanisms of penetrant diffusion in crosslinked networks. These insights can not only guide the engineering of polymer membranes for separation but also expand our understanding of the dynamics of polymers and penetrants in crosslinked networks."]},{"key":"dc:format","label":"Dc Format","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Structural relaxation and penetrant diffusion in polymer networks"]}]}],"canonical_facts":{"dc:contributor":["Sing, Charles E","Schweizer, Kenneth S","Evans, Christopher M","Kuenstler, Alexa S"],"dc:creator":["Lin, Tsai-Wei"],"dc:date":["2024-07-09","2024-08"],"dc:description":["Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2025-02-04 without embargo terms","The student, Tsai-Wei Lin, accepted the attached license on 2024-07-05 at 10:44.","The student, Tsai-Wei Lin, submitted this Dissertation for approval on 2024-07-05 at 11:11.","This Dissertation was approved for publication on 2024-07-09 at 13:30.","DSpace SAF Submission Ingestion Package generated from Vireo submission #20954 on 2025-02-04 at 21:04:15","Controlling the permeation of atomic, molecular, and nanoparticle “penetrants” through dense polymeric media (liquid, glass, crosslinked permanent or dynamic rubber network, thermoset) is a crucial scientific problem broadly relevant in materials, biological chemistry, and energy sciences. In particular, understanding how the many physicochemical factors (e.g., size, shape, and chemistry) and thermodynamic state control penetrant activated mass transport is critical for membrane separations, which serve as promising alternatives to distillation or extraction for chemical separations. A remaining challenge for membrane design is the trade-off between permeability and selectivity described by an empirical upper bound of membrane performance, which the scientific community has been thriving to shift higher through structure/property optimization of membranes. Therefore, we are motivated to explore a new paradigm of using highly-crosslinked networks near glass transition temperature Tg for the selective transport of small molecules. Polymer networks hold promise in membrane separation because dramatic differences in molecular diffusion can result from subtle changes in the network structure. We constructed a coarse-grained molecular dynamics simulation model that reflects the specific polymer chemistry of the network studied, along with experiment and theory done by collaborators, to understand the role that crosslinking has in governing the structural relaxation and the transport of penetrants in polymer networks. We observed a very large increase in segmental relaxation time and glass transition temperature Tg as a result of tight crosslinking and provided a mechanistic microscopic understanding of the observations by showing that structural relaxation involves a coupled local cage and nonlocal collective physics, with the latter becoming more dominant upon cooling. Our investigation of penetrant diffusion reveals that permanent crosslinking can regulate penetrant transport through (1) the near-Tg coupling between penetrant hopping and the structural relaxation of polymer networks (2) the confining mesh that obstructs penetrant motion. We found that the main effect of permanent crosslinking is to slow down polymer structural relaxation and greatly suppress the elementary penetrant hopping event, while signatures of mesh confinement, though of secondary importance, are observed at certain conditions depending on penetrant size and thermodynamic state. The good agreement between experiment, simulation, and theory demonstrated size ratio (penetrant diameter to Kuhn length) as a key variable determining penetrant diffusivity, though the role of chemistry-specific effects (e.g, shape, penetrant-polymer interaction) are non-negligible, as shown in simulation and theory. Finally, we study the bond exchange dynamics and structural relaxation in associative dynamics covalent network (i.e., vitrimers) over wide ranges of crosslink densities fcross, temperatures T, and bond exchange rate. Simulations unravel the intricate interaction between these two dynamic processes and reveal that only when the bond exchange time scale is comparable to Kuhn segmental alpha time will the dynamic crosslinking show noticeable acceleration of segmental relaxation and change in Tg. Overall, we have developed models to connect experimental findings and theoretical predictions for specific polymer networks. These models elucidate the effect of crosslinking on structural relaxation in both permanent and dynamic polymer networks. By combining simulation, experiment, and theory, we identify the mechanisms of penetrant diffusion in crosslinked networks. These insights can not only guide the engineering of polymer membranes for separation but also expand our understanding of the dynamics of polymers and penetrants in crosslinked networks."],"dc:format":["application/pdf"],"dc:identifier":["https://hdl.handle.net/2142/125569"],"dc:language":["en","eng"],"dc:rights":["Copyright 2024 Tsai-Wei Lin"],"dc:subject":["Penetrant Diffusion","Crosslinked Polymer Networks","Glass Transition","Alpha Relaxation Time","Molecular Dynamics","Membrane Separation"],"dc:title":["Structural relaxation and penetrant diffusion in polymer networks"],"dc:type":["text","Thesis"],"thesis:degree_discipline":["Chemical Engineering"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Ph.D."],"thesis:institution_name":["University of Illinois at Urbana-Champaign"]},"updated_at":"2026-07-22T22:25:02Z"}