| dc.description.abstract | The purpose of this research is the preparation of transparent thick film or monolith with high refractive index. Titanium oxide, with a reported refractive index of 2.5 for anatase, can be a suitable inorganic additive in improving the refractive index of organic-inorganic hybrid materials. Epoxy resin, which is in common use of LED’s encapsulation. If titanium oxide and epoxy could be composited into a transparent material, the resulting product would have wide applications. To achieve such hybrid material with high refractive index and good transparency, the particle size of titanium dioxide must be below 10 nm, for otherwise light scattering effect would dominate.
For the synthesis of nano-sized titanium dioxide, tetrachloride (TiCl4) was used as a precursor, followed by hydrolysis and condensation reactions. After washed the white titanium hydroxide gel by water, peptization and crystallization took place in acidic condition. Since peptize size is strongly dependent on the solution concentration, pH and peptizing temperature, the first part of this research was finding the optimum experimental parameters to produce the smallest nano particles dispersible in water.
To disperse titanium dioxide in organic solvent and resin, surface modification of the particles is pivotal. Two aliphatic amines, for instance, n-hexlamine and dodecylamine were modifying agents used in this study. After surface modification with these agents, titanium dioxide can be dispersed in chloroform.
Concurrently, surface modification was done with functional silane, 3-(Trimethoxysilyl) propyl methacrylate (MPS) and 3-Glycidoxypropyl trimethoxysilane(GPS), allowing titanium dioxide to be dispersible in ethylacetate. Having successfully dissolved titanium dioxide, epoxy resin 4221 and EP828 were added.
The as-synthesized TiO2/epoxy thick film is formed from MPS&GPS modified TiO2 and then dispersed in ethylacetate/epoxy 4221 mixture. From thermal gravimetric analysis (TGA), the 8 micron thick film contains up to 50 wt% inorganic material (approximately 45 wt% TiO2 estimated). In addition, the refractive index is measured to be up to 1.70, and it has over 96% transmittance at 600nm wavelength. Nonetheless, such tranparent thick film has a very low glass transition temperature (~70oC), resulting in limited applications.
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