| With the development of the Internet information age,a large number of electronic products and microelectronic devices had come into being rapidly and they had become an inseparable part of human life and work.In addition,the research of scientific instruments and military equipment was also in full swing.However,electromagnetic radiation generated by using many electronic devices and instruments affected the normal operation of precision instruments,and may even completely destroy the function of equipment performance,resulting in data storage,energy and other losses.In addition,electromagnetic interference radiation also was a threat for human health.Therefore,the research on the preparation of electromagnetic shielding materials had become an important topic.Traditional electromagnetic shielding materials were derived from metals or metal alloys,but the disadvantages of high-density,poor erosion resistance and poor toughness of metallic materials limited their applications.Conductive polymer composites had been studied as electromagnetic shielding materials,which ascribe to the excellent properties of light weight,low cost,corrosion resistance,machinability.However,the electromagnetic shielding effectiveness of the conductive polymer composite with low content filler was too low to shield electromagnetic radiation,which ascribe to that the high electromagnetic shielding effectiveness depended on the high conductivity.The high content of conductive fillers would increase the cost and reduce the toughness of the material,limiting the application field of the material.Therefore,conductive polymer composites through structural controlling and designing had been studied for the preparation of high shielding effectiveness materials with low filler content.To prepare conductive polymer materials with low filler content owned high performance shielding efficiency,the structure design and phase regulation of the composite material realized the controllable distribution of the conductive filler to improve the electromagnetic shielding performance of the conductive composite.In this paper,the phase structure of conductive polymer blends was used to control the distribution of conductive fillers to achieve high electromagnetic shielding efficiency,then added the inorganic particles to conductive composites system controlling restricted distribution of conductive fillers to increase the electromagnetic shieldingeffectiveness,controlling the distribution of conductive fillers on the surface of the matrix by chemical deposition method prepared high shielding effectiveness of the conductive composites with the low filler content.As follow showed the main experimental contents:(1)PCL/PLA/MWCNTs composites in different phases were prepared by adding carbon nanotubes(MWCNT)to polycaprolactone(PCL)and polylactic acid(PLA)with different mass ratios.PCL/PLA/MWCNTs composites with sandwich and multilayer structures were prepared by thermal lamination.The effect of PCL/PLA/MWCNTs composites with different phase morphology and multi-layer structures controlling the distribution of conductive filler on electromagnetic interference shielding performance was studied,and the electromagnetic shielding mechanism of different phase morphology and structure was explored.The results shown that the electromagnetic shielding effectiveness of composite was highest among the various phase structures of blends when the mass ratio of PCL/PLA was 10/90.It could be attribute to that the phase morphology of this composite was similar to the island structure,MWCNTs selectively distributed in the PCL phase to form a large number of PCL/MWCNT phase distributing in the PLA matrix,and the PCL/MWCNTs phase forms many small islands to scatter or reflect electromagnetic waves and increase interface polarization,re-reflect waves were absorbed through dielectric losses.The sandwich structure which consisted of symmetric double-layered structure of two PCL/CNT pieces sandwiching pure PLA layer showed highest shielding effectiveness among other blends with multi-layered structure,and higher 20 dB than island structure.This phenomenon attributed to it that impedance mismatch in interface of PCL/CNT layer and PLA layer gave rise to coherent multiple internal reflection between two parallel PCL/CNT layers,and then reflected waves was attenuated by PCL/CNT layers.This study gave a guidance to fabricate conductive composites with high EMI shielding effectiveness by changing phase morphology or structure.(2)Solid glass microspheres(SGM)were added into polydimethylsiloxane/multiwalled carbon nanotube(PDMS/MWCNT)composites causing the restricted distribution of MWCNTs to prepare PDMS/MWCNT/SGM composites with continuous and dense conductive network,whose shielding effectiveness was 12 dB higher than that of the composite without glass microspheres.The effect of the diameter and the content of SGM on electromagnetic shielding effectiveness of the PDMS/MWCNT/SGM composites were investigated.It was found that shielding effectiveness of the composite increased with decreasing the diameter of SGM,while,the electromagnetic shielding effectiveness of the composite did not continuously increase with the content of glass microspheres increased.The electromagnetic shielding effectiveness of composite with glass microsphere content of 30vol% was highest,and the electromagnetic shielding effectiveness decreased when the content of glass microsphere exceeded 30 vol.%.The SGM content would change the conductivity by affecting the distribution of MWCNTs,so the mechanism of electromagnetic shielding was explored by analyzing the microstructure and electrical properties of materials to explain the change of electromagnetic shielding performance.Since the thickness of the conductive layer of PDMS/MWCNT was inversely proportional to the content of glass microspheres,the electromagnetic shielding effectiveness of the composite would reach the optimal value when they reach a balance.(3)A flexible polymer material with high electromagnetic shielding efficiency was prepared by wet chemical deposition with silver nanoparticles on the surface of non-woven cotton fiber(CFs).Ag@CFs non-woven material with a silver content of 1.61 vol.% was prepared by only costing the chemical deposition time of 10 s,which owned a high conductivity of ? 3333 S/m and a high electromagnetic shielding effectiveness of ? 71 dB.When the deposition time increases to 2 minutes,the shielding effectiveness of Ag@CFs non-woven material could increase to ? 110 d B.According to analyze morphology and conductivity of this material,the ultra-high electromagnetic shielding property of the flexible non-woven material was mainly due to the core-shell structure,which owned abundant interfaces and porous structure in the Ag@CFs non-woven fabrics,and the voids in Ag layers.Most electromagnetic waves are reflected at multiple interfaces within the material and then absorbed by dielectric losses.The Ag@CFs non-woven material with special porous and multi-interface core-shell structure achieved the goal of high electromagnetic shielding efficiency of polymer materials with low filler content. |
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