Preparation And Electromagnetic Proferties Of Chiral (Spiral) Substrate And Its Co-Ferrite Composites

In recent years, with the further exploration of traditional absorbing material research, the application of ferrite absorbing material in the electronmagnetic wave absorption and shielding is of common occurrence. However, the applications of ferrites as ideal absorbing materials are limited because of their inherent rigidity, high density, difficult processing and other shortcomings. In order to meet the needs of the development of the absorbing material in the modern production and life, researches devote themselves to research and develop a kind of excellent absorbing material with "thin, light, wide and strong" comprehensive performance. Coiled carbon nanotubes were the optimum material for the microwave absorption as their excellent conductivity, chirality, good dielectric properties and considerable loss of the electromagnetic waves. Chiral polymers, such as chiral polyaniline and polylactic acid, etc, could play a very important role in the field of microwave absorption as their good conductivity and chiral feature, and the good chemical stability, lower density, controllable electromagnetic parameters and easy preparation, etc. Considering the magnetic loss of the ferrite, the chirality and dielectric loss of coiled carbon nanotubes, chiral polyaniline and polylactic acid, and their respective physical and chemical properties, we hope to prepare the two-component composites formed by above three chiral (spiral) materials as the substrate and Co-ferrite. The composites not only have both chirality and good dielectric loss and magnetic loss, but also improved much in stability, density and frequency response. Based on the topic, the main results of this paper are as follows:(1) The coiled carbon nanotubes/Co-ferrite (CCNTs/CFO) composites were prepared by co-precipitation method. The chiral polyaniline/Co-ferrite (L-PANI/CFO) composites were synthesized by co-precipitation method, L-PANI of which was prepared by in-situ chemical oxidative polymerization using L-camphor sulfonic acid as chiral dopant and ammonium peroxydisulfate as oxidant. The polylactic acid/Co-ferrite (PLLA/CFO) composites were prepared by using the ring-opening polymerization of L-lactide and co-precipitation, respectively.(2) The structures of the samples were characterized by X-ray diffraction. The morphologies and particle sizes of the samples were observed by scanning electron microscopy and transmission electron microscopy, respectively. The thermal stabilities of the samples were measured by thermogravimetric analyzer. The results showed that the composites are not simple mixture of each component. There may existed interactions and synergistic effect between them, which further caused a significant change and influence on the structures, morphologies, and functional characteristics of the composites.(3) 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 at room temperature under applied magnetic field. The results revealed that the main factors affected the conductivities included the content of the conductive component, the interactions and synergistic effect between two components. Overall, the conductivities of the composites mainly increase as the increase of conductive components generally. The saturation magnetization of the composites is lower than that of pure ferrite, and decrease as the increase of nonmagnetic components due to the dilution effect of the nonmagnetic component (coiled carbon nanotubes, chiral polyaniline and polylactic acid).(4) The complex permittivity and complex permeability of the composites were tested respectively by an impedance/material analyzer and a vector network analyzer in the frequency range of 1 MHz～3 GHz and 2～18 GHz at room temperature, and the microwave absorption peoperties were calculated by analog method. The results indicated that three composites (CCNTs/CFO, L-PANI/CFO and PLLA/CFO) both possessed of relatively favourable absorbing performance, and have a potential application in the field of microwave shielding and absorption.