Synthesis And Properties Of The Electromagnetic Functionalized Nanocomposites

Nanoscaled magnetic materials (NMM) are important functional materials with wide applications. They are the nanoscaled materials that have been widely used in various industries. Conducting polymers (CP) is a newly arised research topic in 1970's. Among the conducting polymers, conducting polypyrrole (PPy) with conjugated double bond is of great interest because it has the merits of easy synthesis, good antioxidation, high conductivity, easy film forming and high softness, et al. Recently, particular interest is focused on the electromagnetic functioned nanocomposites because the resulting nanocomposite materials exhibit not only excellent magnetic properties but also interesting electrical or optical properties. They have the wide applications in the electromagnetic shielding, microwave absorption, electrochromic device and nonlinear optics, et al. The main content and major results of this thesis are given as follows:1. Spinel ferrites MnFe₂O₄, Mn_0.5Zn_0.5Fe₂O₄ and Mn_0.4Zn_0.3Co_0.3Fe₂O₄ were prepared through substitution of different metal ions via the polymer-pyrolysis method. The magnetic properties of the MnFe₂O₄ and Mn_0.5Zn_0.5Fe₂O₄ measured at room temperature exhibited the super-paramagnetic behavior. However, Mn_0.4Zn_0.3Co_0.3Fe₂O₄ exhibited a ferromagnetic behavior due to the introduction of Co2+.2. Three-dimensional ordered core-shell structured polypyrrole (PPy)-coated polystyrene microspheres (PPy-PS) were synthesized using the polystyrene microspheres as the template. The hollow three-dimensional ordered PPy microspheres can be gained by removing the polystyrene in the tetrahydrofuran. The results showed that conductivity of PPy microspheres at room temperature is higher than the PPy-PS microspheres.3. The electromagnetic functionalized NMM-TiO₂ and NMM-PPy nanocomposites were synthesized and their properties were investigated and discussed.A: MnFe₂O₄-TiO₂ nanocomposites were prepared by hydrolysis of titanium butoxide precursor in the presence of MnFe2O4 nanoparticles. The result showed that real permittivity of the nanocomposites increased with the content of the TiO₂, but the imaginary permittivity of the nanocomposites kept constant and its value was low.B: Synthesis of different electromagnetic functionalized PPy nanocomposites was conducted. PPy-FeOOH nanocomposites were synthesized by one step method. The electromagnetic functionalized PPy-coated M-barium ferrite (MF) nanocomposite powders with high coercive force and residual magnetization and PPy-coated carbonyl iron nanocomposite powders (CIP) with high saturated magnetization were prepared by the chemical synthesis in the presence of MF and CIP, respectively.4. The microwave absorbing behavior of the electromagnetic functionalized PPy composites was investigated in the frequency range of 2¹8GHz. The results showed the MF-PPy nanocomposites (mass ratio of pyrrole to MF=1.0) exhibited the best microwave absorbing properties, and the band width with an absorbing property >10dB and >5dB are 5.4GHz and 7.6GHz, respectively.