Study On The Preparation,Assembly And Property Of Magnetic Nanocomposites

Controlled synthesis and assembly of nanometer magnetic materials is currently the subject of intense research work due to their novel properties, which could have promising applications, such as high-density magnetic recording media, sensors, catalysts, biotechnology, and magneto-optical devices and so on. In particular, it has been attracted much attentions in the fields of biotechnology and high-density magnetic recording media that the use of the nanometer magnetic materials. Therefore, scientists made abroad interests on the study of new nanometer magnetic materials and nanometer magnetic composite materials. In this thesis, we prepared a series of nanometer magnetic composites with polymer materials, and achieved the self-assembly of magnetic materials to developing patterned magnetic films, and the magnetic properties of the prepared materials were investigated in detail.In Chapter Two, we described the synthesis and characterization of magnetic polymer particles prepared by the different two methods of emulsion polymerization and surface-initiated atom transfer radical polymerization. It isdifficult to prepare small magnetic polymer particles (less than 130 nm) by emulsion polymerization; furthermore, the method of surface-initiated atom transfer radical polymerization solved this problem and could achieve the magnetic nanoparticles less than 15 nm. In this chapter, we prepared different diameter magnetic polymer particles by these two methods, and characterized the structure of the magnetic polymer particles in detail, and tested the magnetic properties of the particles. The synthesized magnetic polymer particles have fine magnetism. These results established the groundwork for the using of nanometer magnetic materials in the fields of bioscience, which were used as the medium of magnetic separated materials.In Chapter Three, we prepared two multifunctional magnetic composite particles. We describe the synthesis of bi-functional nanoparticles with super-paramagnetic Fe₃O₄ nanoparticle core and CdS nanoparticles shell, and core-shell nanocomposites of SiO₂/Fe₂O₃ microspheres, by surface-initiated atom transfer radical polymerization. We imported two functional monomer— cadmium dimethacrylate Cd(MA)2 and polymerizable surfactants modified small diameter hematite nanoparticles, during the polymerization of surface-initiated ATRP from initiator modified Fe₃O₄ and SiO₂ nanoparticle surface. The magnetic nanocomposites have both the properties of magnetic nanoparticles and the imported material, which extend the using fields of magnetic materials. These works would supply new methods for preparing functional magnetic nanocomposites.In Chapter Four, we described the construction of patterned magnetic film including magnetic rings, magnetic dots and magnetic strips on the 2D ordered self-assembled monolayers using soft lithography, surface wetting and de-wetting and thermal decomposition methods. Firstly, we presented a simple and controlled method for direct fabrication of ordered 2D arrays of magnetic rings. This method utilizes polystyrene coated magnetite nanoparticles as asolution, and the magnetic rings were fabricated on patterned self-assembled monolayers by dewetting from the solution. Polystyrene coated magnetite nanoparticles were synthesized by atom transfer radical polymerization, which promoted the dispersibility and stability of magnetite nanoparticles in chloroform. This approach offers a new way for patterning nanoparticulate rings with deliberate control over feature composition, size, as well as inter-feature distance. Secondly, we extended the thermal-decomposition technique to the patterned substrates and developed a simple and convenient method for patterning magnetite films by soft lithography and thermal decomposition of Fe(acac)3. In the case, we have prepared multi-patterned Fe(acac)3 films and then transformed the films into patterned Fe3C>4 at the elevated temperature (300°C) in a shorter reaction time than that in the emerging methods. These ordered magnetite patterns would be useful and extended to the fabrication and investigation of some integrated magnetic devices such as the high density magnetic recording materials.In summary, based on the different using of magnetic materials, we prepared multi-kind of magnetic nanocomopsites with polymer materials, and achieved the self-assembly of magnetic materials to developing patterned magnetic films. All of these works would establish the groundwork of the using of nanometer magnetic materials in the fields of bioscience and high density magnetic recording.