Title:
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TiO2 nanorod polymer composite materials
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The remarkable characteristics of Ti02 are widely used, from everyday life
applications (pigments, food/cosmetics additives) to more specialised systems,
including photovoltaics and structural composites. Use in polymers is substantial
(25% of all Ti02 produced), but most applications and research focus on commercial
powders. A new generation of Ti02 nanoparticles has emerged, based on very small,
single-crystals, with well-defined morphology and phase. A limited number of papers
report the use of this new nanoscale Ti02 in polymer nanocomposites, and indicate
improved properties. Although the synthesis of anisotropic nanoparticles (e. g.
nanorods) has been well-reported, use in polymer nanocomposites remains largely
unreported. This thesis broadly covers three topics: (1) synthesis of Ti02 nanorods
using different sol-gel routes in presence of structure directing agents, (2)
modification of the nanorod surface chemistry in order to control dispersion and
surface properties and (3) fabrication of titania nanorod-polymer composites. Singlecrystal
anatase nanorods were produced with variable aspect ratio (3-12), depending
on the specific structure directing agent (SDA) used during synthesis. Due to organic
functionalisation at the nanorod surface, nanorods could be well dispersed in
chloroform. A new procedure, based on the self-cleaning ability of Ti02 under UV,
was developed for removal of organics from the nanorod surface, without
compromising the nanorod morphology, crystallinity or dispersibility. This powerful
tool can be used to change the surface character of the nanorods to generate aqueous
TNR dispersions. Stable dispersions were achieved using quaternary ammonium
hydroxides to modify the surface electrostatically and sterically. Once dispersed
individually, the surface can be further modified by sol-gel chemistry. Composite
work involved blending both organic and water-soluble polymers with nanorod
dispersions in chloroform and water, respectively, to produce composite films of
exceptional optical transparency, even for nanorod loadings up to 30 wt%. The films
possess very strong, wavelength-tuneable UV absorbance, which could be used in UV
filters and optical limiting. The presence of SDAs or dispersants at the nanorodpolymer
interface hinders strong adhesion, as evidenced by marginally lower tensile
strength and thermal stability of the nanocomposites. The photo-stability of the
nanorod composites is comparable to that of the pure polymer and better than that of
composites with commercial equiaxed TiO2 nanoparticles.
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