Preparation And Electromagnetic Properties Of Polyaniline/Expanded Graphite/Co Ferrite Composites

The composites of conducting polymers-inorganic nanoparticles have the functional characteristic of the components, as well as the synergistic effect of the interactions between the components, including the chemical, electrostatic and interfacial interactions. Therefore, they have been applied widely in the fields of mechanics, optics, electrics, and magnetics. They have become the interdisciplinary frontiers of polymers chemistry, solid state chemistry, surface chemistry, and materials science. polyaniline has been most studied because of its easy synthesis, environmental stability, and simple doping/dedoping chemistry. It is interesting if coat expanded graphite with polyaniline, the electrical conductivity and dielectric loss of the composites increase. Meanwhile, if intercalate ferrite particles into the interspace between the expanded graphite layers, the agglomeration of the magnetic particles can be weakened, and the electromagnetic properties can be tuned. The component content of the three-component composites can be adjusted and controled in order to gain the favourable electromagnetic and electromagnetic loss properties. They have an important potential application in electromagnetic shielding and microwave absorption.In this paper, the conducting expanded graphite/polyaniline composites were synthesized by in-situ emulsion polymerization using dodecyl benzenesulfonic acid as dopant and surface active agent, ammonium peroxydisulfate as oxidant. The composites of expanded graphite/Co ferrite were prepared by co-precipitation method. Subsequently, Co ferrite and polyaniline were coated onto these two composites, respectively, yielding two "core-shell" three-component composites with different structures.The structures of the samples were characterized by X-ray diffraction (XRD). The morphologies and particle sizes of the samples were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The thermal stabilities of the samples were measured by thermogravimetric analysis (TG). The results indicated that the two-component and three-component composites are not simple mixture of the components, there may be interactions (including the chemical, electrostatic and interfacial interactions) and synergistic effect between them, which influence the structures, morphologies, and functional characteristics of the composites.The electrical conductivities of the samples were measured by the four-probe conductivity meter. The magnetic hysteresis loops of the composites were determined by using a vibrating sample magnetometer (VSM) at room temperature under applied magnetic field. The results showed that many factors affect the conductivities, such as the content of the conductive components, the interactions and synergistic effect between the components, the conductive network in the composites, the continuity of the polymer chains, conjugated degree and doping level. The conductivities of the composites mainly increase as the conductive components increase. The saturation magnetization of the composites are lower the pure ferrite, and decline as the conductive components increase due to the contribution of the nonmagnetic component (polyaniline and expanded graphite). The interfacial effect influence the magnetocrystalline anisotropy of the ferrite particles and the surface anisotropy of the composites in the polymerization, which results in the decrease of the composites'coercivities.Meanwhile, The permittivity and permeability of the composites were tested on an impedance/material analyzer in the frequency range of 1 MHz-3 GHz. The results demonstrated that the magnetic loss factors (Tanδm) increase and are associated with the volume fraction of the ferrite. The dielectric loss factors (Tanδe) are affected greatly by the the conductive components and their contents. The electromagnetic loss of the composites is a consolidated results of the magnetic and dielectric loss factors. The measurements of the complex permittivity and complex permeability of the composites were carried out by vector network analyzer in the range of 2-18 GHz at room temperature, and the microwave absorption peoperties were analog calculated. The results revealed that the two three-component composites obtained by two pathway are both possessed of favourable microwave absorption peoperties, and have a potential application in microwave shielding and absorption.