| Summary: | 碩士 === 逢甲大學 === 化學工程學所 === 99 === The first part of the study investigated the correlation between thermally responsive wettability switching and surface morphology of poly(N-isopropyla- crylamide) (PNIPAm)-modified ZnO pore-array surface. PNIPAm is grafted on ZnO pore-array surface by surface initiated polymerization. Considering the 3D capillary effect(Wenzel’s model) and air trapping effect(Cassie’s model), the effects of thickness of the PNIPAm layer and surface morphology on the thermally responsive wettability switching behavior of the PNIPAm modified pore-array film were studied. The air trapping effect can be controlled by changing the pore size, the amount of grafted PNIPAm polymer, and the shape of the pore edge. The roughness of the surface and expanding pore edge with mushroom- like texture of the S2 film amplify the thermally responsive wettability switching between hydrophilicity and hydrophobicity. The pore structure is gradually filled with increasing the amount of grafting. When the pore structure is completely filled, it results in the lower switching behavior. Moderately increasing the molecular chain length of the PNIPAm can amplify thermally responsive wettability switching properties. By controlling the ZnO pore-array structure and the amount of grafted PNIPAm layer, the S2 film shows excellent reversibility for more cycles and quick transformation between hydrophilicity and hydrophobicity.
The second is the preparation of gas sensors with porous three-dimensional framework using the TiO2/polymer double-shell hollow microsphere as the templates. PNIPAm was grafted on the TiO2 nanoparticle surface. Its dispersing stability was investigated by centrifugal method. The grafted PNIPAm can increase the dispersing stability of the nanoparticle. The uniformity of the film can be improved by using the PNIPAm encapsulate TiO2 nanoparticle dispersion. After removing the PNIPAm shell by calcination, a solid TiO2 nanoparticle film can be prepared. Besides, double-shell hollow spheres were prepared by encapsulating the hollow polymeric spheres with TiO2 shells. Solid polymeric spheres were used as templates for comparison. The gas sensor of the porous thin film with interconnected three-dimensional pores was prepared by coating the hollow spheres encapsulated with TiO2 and templates removal process. The correlation between the structure and the gas sensing properties of the porous film prepared by packed hollow microsphere was investigated. The response properties of the sensor toward NO2 depend on the type of template and TiO2 film with three- dimensional porous structure. Using the hollow sphere as template helps to prevent the collapse of the hollow microsphere and retain the microporous structure after the template removal process. Compared to TiO2 polycrystalline films, these films showed enhanced gas sensitivity. Such improvement in sensitivity results from the porous structure of the hollow microsphere film which not only increases the active surface area but also promotes the gas diffusion.
|
|---|
