Microwave Absorbing Properties And Mechanism Of PANI/magnetic Particle Composites

As a conducting polymer material, polyaniline (PANI) has elicited the most interest due to its unique properties about optical, electrical and magnetic. Compounded with magnetic components can gain functional composites and widen the use of PANI. The composites of PANI and metallic oxide or metallic ferromagnetic material can be conductors and magnets; their conductivities and magnetism can be adjusted through the control of the content between aniline and inorganic materials in the polymerization. Those composites will become a superior performance microwave absorbing materials.We successfully prepare the PANI/CIP composites by a situ chemical polymerization with carbonyl iron powders (CIP) as magnetic phase in order to improve both electrical and magnetic properties of composites. The composites of PANI/CIP exhibit the strong dielectric loss when the concentration of CIP is low; the main magnetic loss for PANI/CIP can be reached when the CIP content exceeds a critical value and its electromagnetic parameters are enhanced with increasing CIP concentration. It is found that the strongly enhanced EM-wave absorption of PANI/CIP composite should be attribute to the improved electromagnetic property and impedance matching.The composites of PANI/Fe3O4 can be obtained by a situ chemical polymerization with Fe3O4 nanoparticles (coated by oleic acid) as soft-template, APS as oxide, and HC1 as dopant, respectively. The complex permittivity of PANI/Fe3O4 can be modulated by changing both the mass ratios of [Fe3O4]/[ANI] and the molar ratios of [HCl]/[ANI]. It is found that the proper complex permittivity is in favor of enhancing absorbing property. And the diecectrical relaxation behaviours of the composites can be well described using Deby relaxation model.The composites of PANI/CIP/Fe3O4 has been prepared by a facile mechanical mixing with certain mass ratio (such as:7/3 and 5/5) of [PANI/CIP] to [PANI/Fe3O4]. It can be found that the EM-wave absorption property of PANI/CIP/Fe3O4 is the most outstanding compared with both PANI/Fe3O4 and PANI/CIP composites which is due to the electric loss together with magnetic loss and the good impedance matching.Based on the transmit line theory, a complex thickness dA* is introduced for materials with large magnetic loss factor to analyze the electromagnetic wave absorbing properties, where the absolute value of the normalized imaginary part of the complex thickness represents the degree of impedance mismatching and the real part denotes the effective thickness for microwave absorption. Using this method, the intensity and the corresponding material thickness of the reflection loss at each frequency can be well predicted and understood. This method well describes the microwave absorption behaviors of PANI/a-Fe and PANI/a-Fe/paraffin composites. It is found that the global minimum of reflection loss is determined by the energy depletion in the material and the interference cancellation of the incident and reflected waves happens at the air-material interface for the two composites.