奈米氧化鋯粒子表面殘留保護劑時，會對於分散性測試的結果有很大的影響。因此，本研究開發無添加任何保護劑之合成奈米氧化鋯之方法。奈米氧化鋯主要是透過碳酸鋯和氫氧化鈉經低溫水熱法所製備且具有較高的氧化鋯濃度佔整體系統中的25 wt%。奈米氧化鋯的晶相和結晶大小可根據「純鈉比」來進行調控，其「純鈉比」被定義為([Na]-2[CO3])。當「純鈉比」大於0.3時，則可得立方晶之奈米氧化鋯。當「純鈉比」從1.6增加到13.7時，其結晶大小會約從8奈米降至3奈米。 此外，本研究也利用DLVO (Derjaguin-Landau-Verwey-Overbeek)理論來探討表面修飾兩種不同類型改質劑之奈米氧化鋯粒子的分散行為。第一種為表面螯合不同長短碳鏈的有機酸。第二種為表面同時具有疏水性的有機酸和親水性的矽烷。當表面螯合長碳鏈有機酸時，奈米氧化鋯可被分散到介電常數小於7.5的有機溶劑。經固態核磁共振碳譜證實沒有額外的化學物殘留氧化鋯表面。本研究利用「軟鏈接枝模型」分析分散性測試的結果發現有機酸碳鏈的長度必須要大於0.28 nm才能使滲透勢能和彈性勢能在凡德瓦爾勢能變強之前進行抵銷。 奈米氧化鋯可以透過配位體交換法讓表面螯合具有疏水性的有機酸和親水性的矽烷。當表面具有1.90 mmol/g的丁酸和1.34 mmol/g的3-(甲基丙烯酰氧)丙基三甲氧基矽烷時，奈米氧化鋯則具有非常廣泛的分散範圍從非極性有機溶劑的苯到極性有機溶劑的異丙醇。根據DLVO理論的計算，經表面修飾奈米氧化鋯的靜電勢能遠小於位能障礙 (61.72×10-21焦耳，15KBT在298K)即使分散在高介電常數的有機溶劑。因此，奈米氧化鋯能夠具有非常廣泛的分散範圍主要是立體障礙的貢獻。在雙改質劑系統中，選擇適當相對長度的改質劑是一件非常重要的事情，因為當相對長度差距太大時，較短改質劑的性質則會被較長改質劑遮蔽。最後，經表面修飾的氧化鋯可與商用壓克力樹脂混摻且製作出折射率為1.725之奈米複合材料。因此，這樣的奈米粒子技術將可被應用在光學膜領域。 ;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.
