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Title:Mechanochemical activation at solid interfaces
Author(s):Sung, Jaeuk
Director of Research:Sottos, Nancy R.
Doctoral Committee Chair(s):Sottos, Nancy R.
Doctoral Committee Member(s):Moore, Jeffrey S.; Chen, Qian; Evans, Christopher
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Mechanochemistry, Mechanophore,
Abstract:Surfaces functionalization provides an enabling platform for molecular tailoring of the chemical and physical properties of a surface in an on-demand fashion. Prior research has established that self-assembled mononolayer (SAM) functionalization can lead to dramatic changes in surface properties, but there remain significant gaps between understanding cohesive interactions at the molecular level and macroscopic interfacial fracture toughness at SAM-modified interfaces. Characterization and application of surface chemistry changes resulting from activation of force-sensitive mechanophore modified interfaces remains largely unexplored. In this dissertation, two different functionalization approaches to molecularly tailor interfacial changes are investigated. First, the influence of SAM tail group chemistry on the fracture of SAM-modified Si-Au interfaces is characterized. Second, the activation of force-sensitive mechanophore functionalized interfaces is explored. In both approaches, significant changes in interfacial properties are achieved with the application of external force. The interfacial fracture toughness of a SAM-modified Si-Au interface with different tail group chemistry compositions is studied. Thiol and methyl terminated SAMs with varying composition are prepared by surface modification. A modified laser spallation setup and finite element scheme are used to analyze energy evolution during dynamic delamination process. The interfacial fracture toughness of the SAM-modified Si-Au interface increases by 86% with the increase in thiol composition. The computational predictions revealed that plastic energy dissipation plays a pivotal role in energy dissipation in dynamic delamination. The activation of a patterned maleimide-anthracene (MA) mechanophore functionalized epoxy-fused silica interface is characterized with laser-induced stress waves. Active specimens with MA mechanophore covalently bonded at the fused silica and epoxy interface were successfully fabricated. Fluorescence microscopy, X-ray Photoelectron Spectroscopy (XPS), and Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS), confirmed that mechanochemical activation occurring only in active specimens above the threshold activation stress between 149 MPa and 163 MPa. Analysis of the resulting fluorescence showed an ‘on-off’ activation, not observed in bulk mechanochemically active polymers. Local activation of a MA mechanophore functionalized polymer brush-silicon interface is achieved with atomic force microscopy (AFM) lithography. Active specimens with MA mechanophore functionalized between a PGMA polymer brush-silica interface were successfully fabricated. AFM surface topology images, fluorescence microscopy, and ToF-SIMS confirm that mechanochemical activation occurs exclusively in active specimen regions where high contact force was applied. Fluorescence microscopy reveals that as the contact force increases, the degree of activation increases and plateaus eventually. Overall, high spatial and density control of interfacial mechanophore activation is demonstrated with AFM lithography. Finally, the feasibility of mechanically controlled surface-initiated polymer growth using maleimide-furan (MF) mechanophore functionalized surface and AFM lithography is explored. AFM force induced activation of MF mechanophore was confirmed by surface topology imaging, XPS, ToF-SIMS, and fluorescence microscopy. Activation of MF generates maleimide chemical moieties on the specimen surface, that can react with thiol-maleimide-furan (TMF) functionalized molecules dissolved in DMSO solvent. Changes in surface topology and XPS signature confirm that an in situ click addition reaction takes place. This in situ activation-addition reaction shows that mechanophore functionalized surface can be utilized to promote productive chemistry for material fabrication.
Issue Date:2019-03-26
Rights Information:Copyright 2019 Jaeuk Sung
Date Available in IDEALS:2019-08-23
Date Deposited:2019-05

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