Preparation And Properties Of Flexible Polymer-Based Electromagnetic Interference Shielding Composites

With the booming development of communication technology and electronic devices,electromagnetic wave radiation caused by electromagnetic wave leakage will cause serious interference and damage to sensitive electronic components,leading to unstable operation or loss of control of electronic devices in aerospace,weapon equipment,and wearable devices.Moreover,it brings great harms to human blood,immune system,reproductive system and embryo development.To ensure the normal operation of electronic equipment and protect human health,it is necessary to use electromagnetic interference（EMI）shielding materials to block electromagnetic waves.In recent years,the conductive polymer composites（CPCs）with one single or hybrid conductive fillers dispersed in the single-phase or multiphase polymer matrix have taken great attention.Compared with the traditional metal materials,CPCs show a wide application prospect due to their advantages of low density,good flexibility,excellent corrosion resistance,good chemical stability,easy processing and low cost.Nevertheless,to obtain the desirable EMI shielding performances,high filling amounts of conductive fillers are usually needed,which is disadvantageous to the mechanical properties and flexibility of CPCs due to the agglomeration of conductive fillers.Therefore,polymer-based EMI shielding materials that combine flexibility and high EMI shielding effectiveness（EMI SE）is of great importance for EMI shielding systems in areas of aerospace,weapons equipment and wearable devices.Based on this,the flexible co-continuous segregated PU@Ti₃C₂T_x/AgNWs composite films were fabricated via the facile layer-by-layer（LBL）dip-coating hydrogen bonding assembly followed by hot-pressing approach using PU sponge as the three-dimensional（3D）skeleton template.Further,asymmetric（Ti₃C₂T_x@FeCo/ANF）-（Ti₃C₂T_x/ANF）composite aerogels were fabricated by environmentally friendly ice template-directional freezing using aramid nanofibers（ANFs）as the matrix.The microstructures and morphologies of composite materials were characterized analytically by X-ray photoelectron spectroscopy（XPS）,Fourier transform infrared spectroscopy（FTIR）,X-ray diffraction（XRD）,scanning electron microscopy（SEM）,and transmission electron microscopy（TEM）.The magnetic properties,electrical conductivity,EMI shielding properties,Joule heating properties and mechanical properties of the EMI shielding composites were tested by vibrating sample magnetometer（VSM）,Lattice 2258C probe instrument,vector network analyzer,thermo gravimetric analyzer（TGA）and mechanical properties testing.The main conclusions of this paper are as follows:（1）The flexible co-continuous segregated PU@Ti₃C₂T_x/AgNWs composite films were fabricated by facile LBL dip-coating hydrogen bonding assembly followed by hot-pressing approach using PU sponge as 3D skeleton template and Ti₃C₂T_x MXene and AgNWs as conductive fillers.Hydrogen bonding interactions were formed between Ti₃C₂T_x MXene and PU,as well as Ti₃C₂T_x MXene and AgNWs;2D Ti₃C₂T_x MXene and 1D AgNWs are wrapped on the skeletons of open-celled PU foams and interconnected with each other,forming a highly efficient 3D Ti₃C₂T_x/AgNWs conductive network.After hot-pressing,The cocontinuous segregated structures with continuous conductive network and continuous polymer matrix was constructed.Thanks to the co-continuous segregated structure,the flexible PU@Ti₃C₂T_x/AgNWs composite films show high conductivity,excellent EMI shielding performance（88 dB）and Joule heating performance（116.7℃）as well as good mechanical properties and working stability.（2）The flexible asymmetric（Ti₃C₂T_x@FeCo/ANF）-（Ti₃C₂T_x/ANF）composite aerogels with electromagnetic recombination layer and conductive shielding layer were fabricated by environmentally friendly ice-templatedirectional freeze-drying process.Due to the construction of asymmetric structures,electromagnetic waves will undergo a special "absorption-reflectionreabsorption",which gives the composite materials an electromagnetic interference shielding mechanism based on absorption loss.The absorption coefficient（A）of the composite aerogel increases as the ratio of the thickness of the conductive magnetic compound layer to the conductive shielding layer increases.With the increase of the ratio of conductive shielding layer Ti₃C₂T_x MXene to ANFs,the electrical conductivity of the conductive shielding layer of the composite aerogel is gradually increased,and the EMI SE of the composite aerogel is gradually increased.When the thickness ratio of electromagnetic recombination layer and conductive shielding layer is 2:1 and the mass ratio of Ti₃C₂T_x MXene to ANFs is 4:1,the EMI SE of composite aerogel with the density of only 0.024 g·cm^-3 can reach 59.75 dB and the reflection coefficient（R）is only 0.38,which is a guideline for the development of low-reflection polymer-based electromagnetic interference shielding composites.