Constructing High-efficiency Electromagnetic Interference Shielding Composites Based On The Principle Of Reflection And Scattering At Multi-interface

With the high-speed development of electronic technology and the wide use of electronic equipment,the radiation of electromagnetic waves had not to be ignored yet,and electromagnetic interference(EMI)shielding materials came into being.Conductive polymer composites(CPCs)have many advantages in the field of EMI shielding,such as low cost,low density,easy processing.CPCs are usually made of one or more kinds of conductive fillers,which are dispersed in the polymer matrix through a variety of blending ways.Moreover,as an excellent EMI shielding material,not only CPCs need much concentration of conductive fillers inside the composites to improve the polarization loss of electromagnetic waves,but also CPCs require the construction of the conductive interfaces to increase the multiple reflection and scattering loss of electromagnetic waves.In this paper,a series of methods were used to construct EMI shielding materials with superior comprehensive performance based on the design of many conductive interfaces inside the CPCs to enhance the EMI shielding performance.(1)By means of a simple method on electroless plating,silver was coated on the surface of the treated PLA micro-particles,and then the obtained PLA@Ag micro-particles were fused and pressed to form the PLA/silver nanoplates(PLA/Ag)composites.The lateral size of large-area silver nanoplates which were uniformly dispersed in the PLA matrix is directly related to the size of the PLA micro-particles,and the thickness is in nanoscale.The slice thickness and the density of the 2D silver nanoplates depends on the treating time on the surface PLA micro-particles and the concentration of Ag~+,the PLA/Ag composites with compact and complete large-area silver nanoplates exhibited excellent electrical conductivity and electromagnetic shielding performance.According to the value of absorption and reflection on EMI shielding,the enhancement ascribed to the conductive network constructed by the large-area composites in the PLA/Ag composites,which increased its multiple reflection and scattering loss in the conductive interfaces,resulted the great enhancement on the EMI shielding performance at low concentration of silver.The reported method is so simple to obtain PLA/Ag composites with high electrical conductivity and excellent EMI shielding performance.(2)In the experiment above,the PLA/Ag composites confirmed that the construction of conductive interfaces within the CPCs can enhance the EMI shielding performance under low filler content.In order to design better comprehensive property of EMI shielding composites,the distribution of multiwall carbon nanotubes(MWCNTs)in a compatible poly(L-lactide)(PLLA)/poly(oxymethylene)(POM)blend was adjusted by constructing stereocomplex crystallites(SCs),built conductive interfaces by the crystallite exclusion effect.The results have shown that when the content of poly(D-lactide)(PDLA)was 2.5 wt%,PLLA/2.5PDLA/POM/MWCNT composite had the most conductive interfaces and the most complete conductive network provided by the conductive paths,the electrical conductivity reached 5.56 S/m and the EMI shielding effectiveness(EMI SE)reached 20.1 dB with only 0.9 wt%MWCNT in the composites.In addition,the formation of tiny SCs crystals enhanced the mechanical properties of the composites to a certain extent,especially the tensile toughness.(3)Based on the conductive interfaces constructed by the volume exclusion effect in the composites,the flexible CPCs were chosen to design flexible EMI shielding composites.As a third component,the cotton fiber with high length-diameter ratio was chosen to join the flexible substrate--polydimethylsiloxane(PDMS)/MWCNT composites.The adjunction of the CTF not only significantly increased the electrical conductivity of the composites,but also effectively enhanced the EMI shielding performance of the composites.The main reason for the enhancement was that the high aspect ratio of insulated CTF limited the distribution of MWCNT in the PDMS matrix,and created a large number of conductive interfaces to increase the multiple reflection and scattering loss of electromagnetic waves through PDMS/MWCNT/CTF composites,which greatly enhanced the EMI shielding performance.Moreover,due to the flexibility of CTF and excellent interfacial compatibility with PDMS,the tensile strength of the composites had been greatly improved.Furthermore,the electrical conductivity and EMI shielding performance have not changed much even though experienced 6000-time blending.In general,the PDMS/MWCNT/CTF composite was a flexible electromagnetic shielding composite with excellent comprehensive performance by constructed conductive interfaces in the composites,which has great potential in the application of EMI shielding.(4)The above results fully proved that the construction of the conductive interfaces had great enhancement on the EMI shielding performance of CPCs,and the conductive interfaces based on the nanoporous structure could provide a possibility for design of lightweight high-performance EMI shielding composites.Based on the solid POM/PLLA/MWCNT(S-PMLNT)composites,the POM/MWCNT composites with porous structure were prepared through selective etching PLLA chains,solvent exchanging and freeze-drying because of the well compatibility and great solvent difference between PLLA and POM.Although the electrical conductivity of the composites had been reduced,the density was decreased and the EMI shielding performance was greatly enhanced,due to the nanoporous structure constructed by removing PLLA chains which created a large number of conductive interfaces to increase the multiple reflection and scattering loss of EMI waves through P-PMNT composites.In addition,the P-PMNT composites exhibited excellent compression and tensile properties.In general,the lightweight high-performance P-PMNT composites were successfully obtained by design lots of conductive interfaces.