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Title: The mild synthesis of zinc oxide nanoparticles and nanocomposites via hydrolysis of well-characterised zinc organometallics
Author: Orchard, Katherine Lorraine
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2011
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This thesis centres on the development of a clean, one step method for generating surface-functionalised zinc oxide (ZnO) nanoparticles for application in the synthesis of well-dispersed inorganic-organic nanocomposites. The nanoparticle synthesis method utilises the controlled hydrolysis of organometallic zinc compounds, employing diethylzinc as a bulk precursor and an alkylzinc carboxylate as a substoichiometric, secondary precursor to deliver the capping ligands. A series of ethylzinc carboxylate species were synthesised and studied by NMR spectroscopy (EtZn(OOCR); R = H, CH3, and (CH2)nCH3, where n = 4, 10, 16). The ligand stoichiometry of the complexes was found to depend on the nature of the solvent (coordinating vs. non-coordinating), and single crystal X-ray experiments indicated that the strength of the donor interaction of a coordinating solvent affects the nuclearity of the complex‟s repeat unit in the solid state. In addition, the isolated complexes of the acetate derivative were active catalysts for the copolymerisation of CO2 and cyclohexene oxide. The ZnO nanoparticle synthesis route was first explored in the absence of a polymer matrix and was proven to yield hydrophobic nanoparticles with a narrow size distribution without the need for size selection steps (average particle size 3.6 ± 0.2 nm, σ = 15% using stearate; HR-TEM). The effect of varying different synthesis parameters on the resulting ZnO particle size and morphology was investigated. Additional inorganic zinc phases were observed on slowing the reaction rate, allowing insight into the mechanism of delivery of carboxylate groups to the growing nanoparticle surfaces. Finally, in situ ZnO/epoxy resin nanocomposites were prepared. The degree of nanoparticle dispersion improved with surface-functionalisation in the order stearate < uncapped < benzoate (TEM), which correlated with the nature of the particle-matrix interaction (DSC). In situ prepared nanoparticles (uncapped) were also introduced into conventional microcomposites and found to improve the composite density and thermal conductivity relative to the highest loading of microparticles alone.
Supervisor: Williams, Charlotte ; Shaffer, Milo Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available