|dc.description.abstract||The capping agents remained on the surface of the zirconia nanocrystals have an extensive effect on the dispersion test of nanoparticle. In this study, we developed a method for synthesizing zirconia nanocrystals without any capping agents. The zirconia nanocrystals was processed through zirconium carbonate basic hydrate and sodium hydroxide under the low temperature hydrothermal method. The amount of zirconia obtained per batch was as high as 25 wt%. The crystalline and grain size of zirconia was controlled by the net-Na ratio, defined as ([Na]-2[CO3]) with the produced cubic zirconia larger than 1.6, while the grain size decreased from ~8 nm to ~3 nm between net-Na/Zr=1.6 to 13.7.
In addition, the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was employed for explaining the dispersion behavior of nanoparticles grafted with two types of modifier. The first modifier contains different carbon chain length of carboxylic acid chelated on zirconia surfaces. The second modifier comprises hydrophobic carboxylic acid and hydrophilic silane. When the surface chelated with long chain carboxylic acid, the zirconia nanoparticles can be dispersed in dielectric constant less than 7.5 solvents. According to the solid state 13C NMR spectrum, no additional residues remained on the surface of zirconia nanocrystals. The soft-brush model was used to analyze the dispersion test of nanoparticles. According to the model, the length of the ligands must be longer than 0.28 nm in order for the osmotic and elastic repulsion to offset the van der Waals attraction before the latter becomes too strong.
Zirconia nanocrystals grafted with hydrophobic and hydrophilic groups can be prepared by ligand exchange method. When zirconia nanocrystals grafted with 1.90 mmol of BA and 1.34 mmol of 3-trimethoxysilyl-propyl-methacrylate (MPS) per gram zirconia, they can be dispersed from non-polar solvent such as benzene to polar solvent such as IPA. Base on DLVO calculation, the electrostatic potential was far smaller than the energy barrier of 15KBT even in high dielectric constant solvents; thus, our modified zirconia nanoparticles that can be dispersed in broad range of solvents was due to steric effect. Selecting the relative length is very important to the dispersion behavior in dual modified system because when the relative length becomes large, the short modifier would be shielded by the long modifier. Finally, the modified zirconia nanocrystals can blend with the commercial acrylic resin to produce nanocomposite with high refractive index of 1.725. Therefore, this technology of nanoparticle dispersion can be applied effectively to the research of optical film field.||en_US|