| Summary: | 碩士 === 國立中興大學 === 化學工程學系所 === 107 === In this study, we systematically investigate the effect of in-situ polymerization conditions on the magnetic nanoparticle dispersion in the poly(N-vinyl carbazole)/Fe3O4 (PNVK/Fe3O4) nanocomposite films, derived by mixing the surface-modified Fe3O4 magnetic nanoparticles with NVK monomer in DMF solvent or DMF/H2O co-solvent. Four parameters, including the nanoparticle concentration, the grafting density, the reaction temperature and the solvent quality, have been considered as key factors in this study for establishing the relationships between the four paratmeters and their corresponding dispersion morphologies of Fe3O4 nanoparticles in the PNVK matrix.
The present study revealed that the dispersion state of 20 wt% Fe3O4 nanoparticles in the PNVK/Fe3O4 nanocomposites prepared in DMF solvent could be effectively controlled by the reaction temperature. Particularly, three different types of dispersion morphologies (namely, the large aggregates, the small aggregates and the fractal network) have been observed with increasing the reaction temperature. We propose that the interplay between the self-polymerization of monomers (which may lead to the attractive depletion mechanism) and the grafting reaction of monomers onto particle surfaces (which may give rise to the interparticle bridging effect) could play an important role in governing the final dispersion state of Fe3O4 nanoparticles in the PNVK polymer matrix. Furthermore, these different structures led to different magnetic properties. The higher coercivity of Fe3O4 nanoparticles was found in the case of large aggregate structure, while the lower coercivity in the fractal network structure. On the other hand, 20 wt% nanocomposites prepared in the DMF/H2O co-solvent always formed the fractal structure irrespective of the DMF/H2O ratio.
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