Particle Dimension Synergism And Electromagnetic Synergism Of Polydimethylsiloxane Based Composites For High Electromagnetic Interference Shielding Effectiveness And Low Reflection Characteristics

Currently,conductive polymer composites with absorption loss as the dominant mechanism have become a research hotspot in the field of electromagnetic interference shielding materials.Although many studies have achieved improvement on the absorption loss of composite materials,the important role of filler size and distribution in microwave attenuation and enhancement of material absorption loss has rarely been discussed.In addition,the electromagnetic synergistic effect is an important impact on the shielding performance and microwave absorption of composites.Therefore,this study further explores the important role of filler size distribution and electromagnetic synergism in heterogeneous structures on the microwave shielding of polydimethylsiloxane（PDMS）based composites.The research work of this thesis mainly includes the following aspects:First,a stable segregated particle size and multiple segregated particles were constructed by introducing Si O₂particles of different sizes into the polydimethylsiloxane/multi-walled carbon nanotube（PDMS/CNTs）samples.The dispersion of the particles was improved using a solvent-assisted method.Si O₂particles with different dimesion,including micrometer and nanometer sizes,were dispersed in the PDMS/CNT matrix to explore the size effect of the segregated particle surface are on the electromagnetic shielding performance.Multiple Si O₂particles with different sizes,including micrometer-micrometer pairs and nanometer-micrometer pairs,were combined to create composites with multiple interfaces to evaluate the impact of the segregated particle size distribution（multiple interfaces）on the electromagnetic shielding performance.Additionally,the microwave attenuation mechanism of composites with different diameters and various mixed-size Si O₂particles was discussed.Second,Ag-Co bimetallic hollow microspheres（Ag-Co-HMs）with high electromagnetic absorption performance were prepared by modifying the surface of hollow microspheres with highly conductive Ag and magnetic Co.On the one hand,the structure and microwave absorption properties of Ag-Co-HMs were evaluated.Ag-Co-HMs provide a large number of heterojunctions for the accumulation of charges and dipole moments,which helps attenuate microwaves.On the other hand,lightweight and absorptive efficient microwave shielding materials were prepared by adding Ag-Co-HMs to PDMS/CNT composites.The morphology,microwave shielding performance and mechanism of PDMS/CNT/Ag-Co-HM composites were also explored in this study.The hollow and heterojunction structures created gradient impedance,good impedance matching conditions,increased the possibility of microwaves entering the composites,and thus reduced microwave reflection.Finally,based on the efficient enhancement of electromagnetic interference shielding and microwave absorption ability of Ag-Co bimetallic heterostructure,Ag-Co bimetallic two-dimensional microsheets（Ag-Co-MS）were prepared to further explore the microwave attenuation mechanism of electromagnetic synergy.An absorption-type electromagnetic shielding composite material was fabricated at low filler content.The magnetic domain structure and electrostatic force distribution of the Ag-Co bimetallic microsheets were investigated to elucidate their electromagnetic wave attenuation mechanism.Furthermore,a small amount of Ag-Co bimetallic microsheets were incorporated into the PDMS/CNT composites to achieve efficient electromagnetic shielding and enhanced absorption loss at a low filler content.