Structure analysis of titanate nanotube/organic molecule hybrid and self-healing polymer Public Deposited

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  • March 22, 2019
  • Jia, Yuanyuan
    • Affiliation: College of Arts and Sciences, Department of Physics and Astronomy
  • In this dissertation I report the structure and property characterization of two kinds of materials on the micro- and nano-scale level, the self-healing polymer Surlyn and a titanate nanotube/organic molecule hybrid. Multiple techniques have been utilized to study the structural, dynamic, thermal, and optical properties of the materials. In the first study, the thermal, structural, and dynamic properties of the self-healing polymer Surlyn (poly(ethylene-co-methacrylic acid) polymer neutralized with Na+) were investigated. By introducing a suitable cation, Na+ e.g., Surlyn possesses unique properties, such as the intriguing property of self-healing. Understanding the role of the cations in the material, the chemical structure and the physical properties of the polymer is crucial for potential applications. The thermal property of Surlyn is characterized by differential scanning calorimetry (DSC) and microscopic structures are studied by NMR. It is found that although thermal properties change significantly, the structure and dynamics of ionic aggregates (consisting of Na+-O- pairs) remain unchanged under aging and mechanical deformation. The distance between Na+ ions was also estimated. In the second study titanate nanotubes were successfully synthesized. Titanate nanotubes have great potential for applications in photocatalysis due to their unique structural and photocatalytic properties. However, their wide band gap, 3.7 eV, and the Ti defect sites present problems for the photovoltaic applications Surface modification, e.g. attachment of charge-transfer ligands, is one of the most effective approaches to modify the optical absorption spectrum and restore the sixfold coordination of Ti sites. In order to study the mechanisms of bonding between titanate nanotubes and the charge transfer ligands, I chose three different molecules, hydroquinone, 4-methoxypenol(MEHQ) and catechol. Each of these three molecules is expected to form different bonding configuration. The optical and structural properties of titanate nanotubes and the three hybrid structures (titanate nanotube/hydroquinone, titanate nanotube/MEHQ and titanate nanotube/catechol) are characterized by multiple techniques, such as UV-vis, Raman spectroscopy, X-ray diffraction and NMR spectroscopy, etc. It is found that by forming a bidentate structure, organic molecules (hydroquinone and catechol) and titanate nanotubes can form hybrid structures which are relatively stable in the aqueous environment. Also, it was demonstrated that there are significant differences in local structures between water-washed and acid-washed titanate nanotubes. For acid-washed nanotube, the local structure can be changed reversibly into an anatase-like structure by the incorporation of HQ, MEHQ, or CAT. This provides important clues for understanding the structure of titanate nanotubes and the interaction between ligands and nanotube surfaces. The hybrid system of titanate nanotubes/organic molecules has optical absorption significantly beyond 700 nm. This system could have very important applications in photocatalysis and photovoltaic devices.
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  • Wu, Yue
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  • University of North Carolina at Chapel Hill
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