| In recent years,conductive polymer composites(CPCs)have been widely used and rapidly developed in the field of electromagnetic protection due to their low density,good processing and forming property,adjustable electrical conductivity and corrosion resistance.However,in the face of the electromagnetic protection needs of the new generation of integrated,wearable,intelligent and other high-yield thermal electronic devices,the necessary thermal conductivity functional design of CPCs electromagnetic interference shielding materials has become an important development direction of new electromagnetic interference shielding composites.Based on the current design strategy of multi-interface structure control for high efficiency shielding materials,a multi-interface conductive network is built inside the composite material to achieve the ideal shielding efficiency under low fillers loading is an useful method.However,the introduction of multiple interfaces into the polymer matrix with low thermal conductivity will reduce the phonon transmission ability of the composite material,which greatly increases the difficulty of optimizing the thermal conductivity of the electromagnetic shielding material.It is difficult to meet the requirements of high electrical conductivity and high thermal conductivity of the material in the field of electromagnetic protection at the present stage.Therefore,this paper takes high thermal conductivity and high shielding electromagnetic shielding material as the research target,starting from the structure control and molding strategy of CPCs,realized the conductive polymer matrix-effective building thermal conductive network,solves the problem that it is difficult to realize high thermal conductivity and high electromagnetic interference shielding effectiveness at the same time,and finally obtains the efficient electromagnetic shielding material has the function of thermal conductivity.Relevant research contents are as follows:(1)Non-woven fabric(NWF)composite film coated with silver(Ag)layer was prepared by controllable loading of metal on three-dimensional disordered fiber surface by chemical deposition process.A flexible,efficient and reliable electromagnetic interference shielding composite film with good mechanical properties and shielding reliability was prepared by composite film with waterborne polyurethane(WPU).Thanks to the effective construction of3D metal network with high electrical conductivity and thermal conductivity,at the Ag load is10.5 wt%,the electrical conductivity reaches 31746 S/m,and the electromagnetic shielding efficiency reaches 72.5 d B.Moreover,due to the effective transfer of tensile stress by this structure,the tensile strength of the composite film reaches 12 MPa,and Young's modulus reached 257.2 MPa.The second network was constructed by introducing graphene loaded Fe-Co(Fe Co@rGO)magnetic thermal conductivity particles into the WPU.Due to the highly efficient hysteresis loss capacity and the unique"absorption-reflection-reabsorption"electromagnetic loss mechanism,the electromagnetic shielding efficiency of the composite material was improved to 77.1 d B.The 2D thermal conductivity filler is easier to lap between the three-dimensional Ag networks,providing more phonon transmission paths,and realizing the optimization of thermal conductivity of the composite material(1.65 W·m-1k-1).(2)Based on the exploration of prefabricated network-resin backfill forming thought in the previous chapter,it is crucial to build a prefabricated network with controllable size and morphology for the performance optimization of composite materials.In this chapter,a reduced graphene oxide(rGO)aerogel with highly controlled electrical conductivity and oriented bubble pores was prepared by ice template combined with high temperature heat treatment,and a flexible and efficient electromagnetic shielding composite material was prepared by composite with PDMS flexible resin.At the heat treatment temperature of 1000?,the electrical conductivity of rGO aerogel reaches 242.7 S/m,which endows the rGO/PDMS composite with excellent efficient EMI SE of 40.6 d B.Hexagonal boron nitride(hBN)with dielectric and thermal conductivity properties was introduced to make hBN evenly arranged in the orientation bubbles of the rGO prefabricated network,so as to realize the effective construction of the electrical-thermal double network.Moreover,because the regular C=C structure of rGO can efficiently transmit phonons,hBN can perform dielectric loss on electromagnetic waves.Therefore,the electromagnetic shielding and thermal conductivity of the composite were optimized by the two networks.The electromagnetic shielding performance was improved to 43.1 d B,and the thermal conductivity reached 1.19 W·m-1k-1 when the load of hBN was 20 wt%.(3)Based on the high design ability of the prefabricated network forming idea,the low reflection characteristics of the thermal conductive electromagnetic shielding composites were controlled.The multi-walled carbon nanotubes/silver(MWCNT/Ag)multilayer conductive network was prepared by directional freeze drying combined with heat flux assisted process.The conductive gradient was obvious from top to bottom.In addition,MWCNT/Ag/hBN/PDMS composites with highly adjustable thermal conductivity and shielding properties were prepared by constructing an efficient thermal conductivity network with hexagonal boron nitride/polydimethylsiloxane(hBN/PDMS).By means of the layer by layer loss of the gradient conductive network to the electromagnetic wave and the dielectric loss of the hBN packing to the electromagnetic wave,the EMI SE of the composite material in the X-band reaches 69 d B,and because of the gradient structure design with low surface conductivity and the introduction of hBN with low dielectric,the R value of the composite material is reduced to 0.18.To achieve the low reflection characteristics of the composite material with high electromagnetic shielding efficiency.At the same time,the MWCNT/Ag prefabricated network and hBN are bridged to each other to transfer phonons efficiently,which makes the thermal conductivity of the composites reach 0.6 W·m-1k-1. |
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