Structural Control And Properties Research Of Electromagnetic Interference Shielding Polymer Composites With Low Reflection

In recent years,facing the electromagnetic protection needs of the new generation of lightweight,intelligent,and wearable electronic equipment,conductive polymer composites?CPCs?for electromagnetic interference shielding have received widespread attention and got rapid development.Compared with traditional metal materials,CPCs show the advantages of low density,good processability,adjustable conductivity,and corrosion resistance.According to the principle of impedance mismatch,CPCs with high conductivity can show excellent electromagnetic shielding performance due to the severe surface electromagnetic wave reflection.Therefore,the current research direction of electromagnetic shielding materials tends to use new highly conductive materials or corresponding structural designs to obtain excellent conductive properties.However,such materials rely on severe surface reflections cannot fundamentally solve the problem of electromagnetic interference,as their reflectivity?R?often exceeds 90%to cause serious secondary electromagnetic interference.Therefore,using the magnetic and dielectric loss of magnetic and dielectric materials to reduce electromagnetic wave reflection is becoming a research hotspot in the current electromagnetic shielding field.However,due to the limitation of impedance mismatch,reducing reflection and improving electromagnetic shielding performance are mutually restricted.As a result,in the current research,low-reflection electromagnetic shielding materials are difficult to obtain idea shielding performance,and the excessively high reflectivity of high-shielding materials cannot be effectively adjusted.Therefore,this paper takes the low reflection and high shielding electromagnetic shielding materials as the research target,based on the structural control of CPCs to realize the design and regulation of low reflection electromagnetic shielding network.And solved the contradiction between reducing the reflectivity and improving the electromagnetic shielding performance in the existing research.The efficient electromagnetic shielding materials with significantly low reflection characteristics are finally obtained.The relevant research content is as follows:?1?Utilizing the controlled loading of metal on the surface of polymer particles by chemical deposition technology,ultra-high molecular weight polyethylene?UHMWPE?polymer composite particle coated with a dense metallic nickel?Ni?layer was prepared.The composite GTR/UHMWPE@Ni with double matrix was prepared by blending with ground tire powder?GTR?particles and hot pressing.Benefiting from the high melt viscosity of UHMWPE and the inherent 3D cross-linked structure of GTR,the nickel layer is selectively distributed at the interface between the two substrates,and cooperates with the semi-percolation carbon black?CB?network inherent in the GTR substrate to construct a“Magnetic conductive metal-Carbon”hybrid network.Based on the design of hybrid network,when the Ni content is only 1.04 vol%,the electrical conductivity of the material is 62.5 S/m,and the electromagnetic interference shielding effectiveness?EMI SE?reaches 47.3 dB.In addition,the material exhibits obvious low reflection characteristics.By adjusting the Ni content in the hybrid network,the reflectivity of the composite material is reduced to 0.58 at 0.71 vol%Ni content,and simultaneously,an effective electromagnetic shielding effectiveness of 30.8 dB is obtained.?2?Employing the synthesized reduced graphene oxide decorated with ferroferric oxide?Fe₃O₄@rGO?nanoparticles and highly conductive multiwalled carbon nanotube?MWCNT?as functional fillers.The multilayer Fe₃O₄@rGO/MWCNT/WPU flexible composites were prepared by using layer-by-layer casting method.The composite was composed of three layers of Fe₃O₄@rGO/WPU absorption layer in front and one MWCNT/WPU reflection layer in back.By regulating the rGO content of each absorption layer,the controllable positive conductive gradient and negative magnetic gradient along the incident direction of electromagnetic waves were established.Leading the incident electromagnetic waves suffer from a special“absorption-reflection-re-absorption”process,and thus realize an absorption dominated shielding mechanism.The composite exhibits significant low reflection characteristics and effective EMI SE.By increasing the electromagnetic gradient and MWCNT content,the R value can be reduced to 0.27,and the EMI SE can be increased to 35.9 dB.The low reflection characteristics and electromagnetic shielding effectiveness are controlled in the same direction.?3?First,the gradient multilayer Fe₃O₄@rGO/MWCNT/WPU composite in the previous chapter was defined as ar.The effect of a-layer thickness on the electromagnetic shielding performance and the relationship between the MWCNT content and the R were further studied.By matching the a-layer and the r-layer,the R value of the ar composite was further reduced to0.24.Based on the structure and preparation of ar,the raar,arar and arra with different electromagnetic gradient directions were prepared through the gradient stacking.For raar,the a-layer with gradient structural design is placed between the parallel r-layers to form a sandwich structure like resonant cavity.The raar composites exhibit ultra-efficient EMI SE,and the value is as high as 83.3 dB.The arra composites exhibits device characteristics:electromagnetic wave conversion and re-emission,which greatly decrease the EMI SE of composites.As the arar show both the electromagnetic wave response characteristics of raar and arra.Thus,the arar was endowed with high-efficient EMI SE,and meanwhile,showing electromagnetic wave emission behavior.By regulating the a-layer and r-layer,the EMI SE of arar can be arrived at55.7 dB,and the corresponding R value is only 0.28.