| Up to now, the conventional method of preparing conductive polymer/inorganic nanocomposites is that inorganic particles have been synthesized and embedded in the polymer matrix via in situ polymerization or precipitation method. Most of the target products show a core-shell structure, the main drawback is that inorganic nanoparticles aggregate easily, so it must be dispersed via ultrasound or dispersing in a medium after the surface modification to carry on the subsequent complex process.In view of the nitrogen atom of aniline having a lone pair of electrons, aniline can form complexes with many transition metal ions. Therefore a new method for growth of inorganic nanoparticles in the polyaniline matrix is designed in the present work. The specific steps are as follows:Firstly, polyaniline doped with transition metal ions (Mn+) was synthesized by oxidative pomerization of aniline complexes with metal ions (Mn+); Then, the non-doped polyaniline-based nanocomposites were prepared by subsequent thermal process in which the metal ions source in the polyaniline chains gradually nucleation, growth and crystallization to form the inorganic nanoparticles in polyaniline matrix; Finally, the novel nanocomposites with both conductivity and magnetic properties were obtained by doping with appropriate acid (SSA). This method is named as "coordination-polymerization-hydrothermal" method in the present work. The specific studies and results are as follows:(1) Firstly aniline monomer is utilized for coordinating with metal ions (Mn+) and polymerization by adding oxidant (NH4)2S2O8(APS), forming the polyaniline doped with metal ions (Mn+). The effects of different metal ions on the morphology of as-synthesized polyaniline are characterized by the scanning electron microscopy (SEM). The results indicate that the type of metal ion content, the coexistence of different metal ions and the temperature of the polymerization process have a huge effect on the morphology of as-synthesized polyaniline.(2) The PAn-FeOOH, PAn-CoFe2O4and PAn-CoLao.15Fe1.85O4nanocomposites were prepared by a novel "coordination-polymerization-hydrothermal" method, and doped by sulfosalicylic acid. The influence of reactants ratio and concentration of doping acid on electromagnetic properties of resulting composites was investigated. The micrographs, structure and electromagnetic properties of nanocomposites were characterized by the scanning electron microscopy (SEM), X-ray diffraction (XRD), FT-IR spectroscopy and electromagnetic measurements.(3) For the PAn-FeOOH nanocomposites, when the content of FeOOH in composites is24.12wt%, the conductivity is about0.83S/cm, and the thickness of composites is at3mm, a maximum reflection loss of -33.75dB at12.88GHz is observed with a bandwidth of6.14GHz above-10dB loss; For the PAn-CoFe2O4nanocomposites, when the content of CoFe2O4in composites is8.86wt%, the conductivity is about0.43S/cm, and the thickness of composites is at2mm, a maximum reflection loss of-16.71dB at16.01GHz is observed with a bandwidth of4.68GHz above-10dB loss, and different thicknesses exhibit different absorbing properties; In terms of the PAn/CoLaxFe2-xO4nanocomposites, the optimal microwave absorption performances are under x-0.15, that is the substitution ratio of La is7.5%, when the content of CoLaxFe2-xO4in composites is8.23wt%and the conductivity of composites is about0.833S/cm. When the layer thickness is2mm, the maximum reflection loss reaches to a maximum-42.65dB at15.91GHz with a bandwidth of6.14GHz above-10dB loss. The nanocomposites exhibit excellent microwave absorbing capacity and can meet the necessary requirements for high-performance absorbing materials with "light, thin, strong, and wide".(4) The electromagnetic properties of the PAn-FeOOH, PAn-CoFe2O4and PAn-CoLa0.15Fe1.8504nanocomposites are compared and the absorbing mechanism is discussed in the article. It is found by comparing microwave absorbing properties of each composite that in addition to the conductivity, magnetic permeability and impedance matching of the components, the specific surface area, interface effect and pore features of the nanocomposites have a great impact on its microwave absorbing properties. The results also found that with the increase of the thickness of PAn-CoLa0.15Fe1.85O4nanocomposites, the absorption peak number increases gradually from the original one to two and three, and the absorption peak located at the low, mid and high frequency position. The results have a guiding role to the future microwave-absorbing materials for tailoring and regulation according to practical requirements. |
PDF Full Text Request