Synthesis And Characterization Of Magnetic Conducting Nanosized Polymer Microspheres With Core-shell Structure

Recently, magnetic conducting polymer composites with both electrical and magnetic properties have received tremendous attention, and study on this kind of composites has become one of the most active and promising research fields. What makes inorganic/conducting polymer composites so attractive is their potential applications in batteries, electro-chemical display devices, molecular electronics, electro-magnetic shields, and microwave-absorbing materials. So far, although numerous synthetic routes, such as suspension polymerization, emulsion polymerization, dispersion polymerization, etc, have been developed to produce magnetic composite microspheres, there are still a lot of problems need to be resolved for preparing ideal and useful magnetic conducting composite microspheres. These problems include low magnetization, big size, polydispersity of particle size, low efficiency of encapsulation and so on.It is realized recently that the preparation of high quality magnetic conducting composite microspheres relies on the breakthrough of synthesis approaches and the detailed understanding of the polymerization mechanism in the presence of magnetic inorganic particles. The main objective of this dissertation is to prepare strong magnetic nanoparticles, to develop novel method to prepare magnetic conducting composite microspheres within nanometer, to find the relationship between the structure of composite microspheres and the preparation method, and to elucidate mechanism of preparation. In this paper Fe₃O₄ was doped with rare earth elements of great magnetic moment and the rare earth Fe₃O₄/conducting polymer nanosized microspheres were prepared by emulsion and microemulsion polymerization. The magnetic particles and magnetic conducting composite microspheres were characterized by TEM、XRD、FI-IR、ICPAES and TGA. The structure of microspheres, forming mechanism, electrical and magnetic properties and thermal stability were studied respectively. At the same time the vibrating sample magnetometer was used to determine and study the magnetic responsibility of rare earth doped Fe₃O₄ particles and composite microspheres.The Fe₃O₄ magnetic fluid was prepared by oxidation method, chemical coprecipitation method and microemulsion method, respectively. The optimized reaction condition and parameter were obtained by investigating the influence of surfactant concentration on particle diameter and its distributing, and influence of heating temperature and time on Fe₃O₄ magnetic property. There were some differences in the particle diameter, crystal structure and magnetic property of nanoparticles prepared by the three methods. To obtain inorganic nonoparticle with higher saturation magnetization, we used a novel method to synthesize La/Ce/Ni/Nd/Co doped Fe₃O₄ particles, and then the effects of the species of rare earth on magnetic responsibility were discussed. The specific saturation magnetization of La/Ce/Ni/Nd/Co doped Fe₃O₄ was higher considerably than that of pure Fe₃O₄. La/Ce/Ni doped Fe₃O₄ particles are superparamagnetic.The magnetic conducting Ni-doped Fe₃O₄-PPy polymer microspheres with average diameter of 70-85 nm were successfully synthesized in the presence of the nano-sized Ni-doped Fe₃O₄ magnetic particles. The results show that the resulting microspheres contained Ni-doped Fe₃O₄ nanoparticles and polypyrrole, and there were interactions between them as a result of shifting of XRD diffraction angle and FTIR wavenumber. The results of themogravimetric analysis showed that Ni-doped Fe₃O₄ nanoparticles improved the thermal stability of nanospheres, and the interactions existing between Ni-doped Fe₃O₄ nanoparticles and polypyrrole were confirmed again. The major factors influencing the magnetic property were analyzed, and the specific saturation magnetization of Ni-doped Fe₃O₄-PPy polymer microspheres increased with increasing Ni-doped Fe₃O₄ content. The conductivity of Ni-doped Fe₃O₄-PPy nanospheres depended on Ni-doped Fe₃O₄ content and its dispersibility. The conductivity of Ni-doped Fe₃O₄-PPy nanospheres is three orders of magnitudes higher than that of Ni-doped Fe₃O₄ nanoparticles. The conductivity was increased first and then decreased as the increasing of Ni-doped Fe₃O₄.Fundamental research on the microemulsion polymerization to prepare magnetic conducting nanocomposite microspheres was carried out. The work mainly focused on the final particle size, size distribution and magnetic properties of the composite microspheres. The magnetic conducting nanocomposite microspheres Ce-doped Fe₃O₄-PPy and La-doped Fe₃O₄-PANI with better size distribution and structure, and ideal magnetic properties were synthesized via microemulsion polymerization of aniline or pyrrole monomer. Their structures and properties were also characterized by TEM, IR, XRD, VSM, TGA and ICPAES. The results showed that the resulting microspheres of Ce-doped Fe₃O₄-PPy and La-doped Fe₃O₄-PANI were almost spherical with diameters 50-75 nm and 25-85 nm respectively. Two nanocomposite microspheres presented better core-shell structures and dispersibility than that of Ni-doped Fe₃O₄-PPy prepared by emulsion polymerization, and polymer covered the magnetic nanoparticles completely. Furthermore, the interaction between the magnetic particles and polypyrrole or polyaniline chains improved the thermal stability of nanocomposites. The specific saturation magnetizations of nanocomposite microspheres, Ce-doped Fe₃O₄-PPy and La-doped Fe₃O₄-PANI, depended on the inorganic magnetic nanoparticles, and they increased with increasing amount of Ce or La and Fe₃O₄ content. By controlling parameter, superparamagnetic nanocomposite microspheres La-doped Fe₃O₄-PANI with specific saturation magnetization 17.51 emu/g and conductivity 19.4×10^-4s·cm^-1, and Ce-doped Fe₃O₄-PPy with specific saturation magnetization 25.1 emu/g were prepared by microemulsion polymerization. So this novel La-doped Fe₃O₄-PANI composite material could be used for electrical-magnetic shields and microwave absorbing materials owing to its good electrical and magnetic properties.By comparing the emulsion polymerization with microemulsion polymerization, it can be concluded that the microemulsion polymerization is a better and more promising method because it can prepare magnetic conducting polymer micrespheres with good size distribution and core-shell structure, well electrical and magnetic response, and high efficiency of encapsulation.