Papers by Author: X. Hu

Abstract: Titania/organically modified silane hybrid thin films for photonic applications were prepared by combining a low temperature sol-gel technique and a spin-coating process from an organic-inorganic hybrid system. Effects of the titanium content and heat treatment temperature on the structural and optical properties of the hybrid thin films were characterized by atomic force microscopy and UV-visible spectroscopy. It is found that the optical and microstructural properties of the hybrid thin films depend on the heat-treatment temperature and titanium molar contents. The thickness and the refractive index of the hybrid thin films were also measured and found to be related to the heat treatment temperature and titanium molar content. These results indicate that a dense and high transparent hybrid thin film can be obtained at a low heat treatment temperature. Potential photonic device structural patterns can easily fabricated from the as-prepared hybrid thin films by using etching process.

Abstract: Titania/organically modified silanes (ormosils) organic-inorganic hybrid thin films doped with azobenzene small molecules are prepared by a low temperature sol-gel spin-coating process for optical switch applications. Acid-catalyzed solutions of γ-glycidoxypropyltrimethoxysilane and methyltrimethoxysilane mixed with tetrapropyl orthotitanate are used as matrix precursors. Atomic force microscopy is used to study the morphological properties of the hybrid thin films. Results indicate that crack-free thin films with a thickness of about 1.3μm can be obtained by a single spin-coating process after a low heat treatment temperature. The propagation mode properties of the hybrid thin films are also studied by employing a prism coupling technique. The photo-responsive properties of the hybrid films baked at different temperatures are induced by an irradiation with UV light and subsequent visible light.

Abstract: The effects of compatibilization and mould geometry on the fibrillation of liquid crystalline polymer were investigated in this study. The blend is composed of polycarbonate (PC) and LC5000, a thermotropic liquid crystalline polymer consisting of 80/20 wt% of hydroxybenzoic acid and poly(terephthalate). The effect of compatibilization was investigated by studying the morphological properties of injection moulded plaques and significant enhancement in the fibrillation of LCP was observed in the moulded samples after addition of the compatibilizer. The effect of mould geometry was studied by comparing results obtained from three types of specimens, namely, specimens cut from large rectangular plaques, moulded rectangular bar specimens and molded dog-bone specimens. It was found that mould geometry had a direct influence on the magnitude of the elongational and shear stresses in the melt during molding and thus affected the degree of LCP fibrillation. Moreover, it was observed that the constriction at the “neck” of the dogbone geometry actually facilitated development of LCP fibre in the blend by increasing shear stress during moulding and promoting LCP fibre coalescence.