Preparation Of Functional Conductive Particles And Its Application In Electromagnetic Shielding Materials

The microstructure and composition of functional conductive particles haveimportant influence on the electromagnetic response characteristics of the materials.The use of simple,effective,and inexpensive way to fabricate doped PANI with micro/nanostructures has become one of the hotspots in this field.In this dissertation,the formation mechanism of doped PANI with microstructures,the relationship between the structure and electromagnetic shielding performance are investigated in details.The mechanism of electromagnetic shielding is also proposed.In addition,the application of the obtained functional conductive particles in polymer-based electromagnetic shielding composites is investigated.The main research contents are as follows:?1?Dope-PANI nanoparticles with specific micromorphologies were synthesizedin aqueous solution by using template-free chemical oxidation polymerization.The results showed that the shielding efficiency of PANI increases with the increase of acid concentration.With the increase of reaction time,the shielding efficiency shows the trend of increased first and then decreased.The types of doping acids had a significant effect on the microstructure of PANI.The PANI doped with camphorsulfonic acid and PANI doped with hydrochloric acid showed sea cucumber-like morphology,while the PANI doped with phosphoric acid and sulfuric acid presents the nanofiber morphology.By comparing the chemical structure,grain size,and d-spacing,it was found that the degree of oxidation and crystallinity of PANI varied with the type of doped acid.The results also indicated that the nanoparticles with coarse and microstructure increase the contact point between electrons in the particles,resulting in the enhancement of the electrical conductivity and electromagnetic shielding effect.The as-prepared PANI exhibits the electromagnetic shielding properties mainly based on the absorption loss.Among these materials,PANI doped with camphorsulfonic acid exhibits the highest electrical conductivity(1.28±0.17S·cm^-1)and an excellent electromagnetic interference?EMI?shielding effectiveness?SE?with 22dB?thickness of 0.35mm?in the X-band was achieved.?2?BF@PANI composite particles with core-shell structure were prepared byusing in situ chemical oxidative polymerization method.The as-prepared BF@PANI composite adopted the natural and inexpensive BF as its core and the PANI as the shell.The results show that with the increase of the amount of aniline,the EMI SE increased first and then decreased.The EMI SE increased with time and increased slowly after 4 hours.There existed chemical interaction between BF and PANI cladding.The doping rate and crystallinity of the PANI layer were improved.The BF@PANI composite exhibits superior electrical conductivity(201±0.29S·m^-1),which is higher than that of the pristine PANI homopolymer(135±15 S·m^-1)prepared under the same experimental conditions.The comparison between the theoretical calculation and the experimental results indicates that the enhancement of electromagnetic properties for the BF@PANI composite is due to the core-shell architecture,which could induce the multiple reflections of electromagnetic wave.The composites show absorption dominated total EMI SE of 28.8 dB at a thickness of 0.40 mm in the X-band.?3?On the basis of the above research,the PANI and BF@PANI are used asfunctional composition in the electromagnetic shielding material.On the one hand,electromagnetic shielding materials were obtained by in-situ polymerization of PANI on the surface of nonwoven fabric?NW?with camphorsulfonic acid as the doping acid.The results show that the deposition amount of PANI increases with the prolongation of the reaction time.The composites with thin thickness,compact structure,and high shielding efficiency could be obtained after compression treatment.The EMI SE is up to 40.8 dB at the thickness of 1.10 mm.On the other hand,both of PANI and BF@PANI were used as the conductive fillers,a series of polyvinyl butyral?PVB?-based electromagnetic shielding films were prepared through the solution casting method.The results show that compared with PVB/PANI,the conductive network in the PVB/BF@PANI composites is more likely to form due to the fiber-like property of BF@PANI.The PVB/BF@PANI exhibits high conductivity and shielding efficiency.In addition,the dielectric loss and shielding efficiency of PVB/BF@PANI composites increased with the BF@PANI content.