Preparation And Properties Of Mxene/Polymer Electtomagnetic Interference Shielding Nanocomposites

The rapid development of communication technology and the popularity of wearable electronic devices,gradually aggravate the electromagnetic radiation pollution,which not only interferes with the normal work of high precision instruments,but is harmful to the human health,and therefore it is urgent to develop high-performance electromagnetic interference(EMI)shielding materials to alleviate or even eliminate the pollution.With the advantages of light weight,corrosion resistance,easy processing,versatile property tunability,polymer-based EMI shielding nanocomposites have attracted more and more attention.As a new kind of nanomaterial,two-dimensional transition metal carbide/nitride(MXene)has both high electrical conductivity and rich surface groups,which has significant advantages in the preparation of polymer-based EMI shielding nanocomposites.However,in some applications,there are still some problems.For example,the adhesion of MXene to most of polymer substrates is weak,and its structure is unstable in wet environment,so the EMI shielding coating has weak adhesion to the substrates and poor environmental stability.In addition,it is difficult to combine the excellent EMI shielding performances with low thickness for MXene-based polymer nanocomposites.Besides,MXene nanosheets are not easily dispersed in the hydrophobic polymer matrix,especially in inert polyolefins,so it is difficult to prepare polymer nanocomposites with excellent electromagnetic shielding performance at low MXene contents.In this work,MXene nanosheets are used as conductive fillers for waterborne polyurethane and polypropylene,respectively.Using new strategies and reasonable structure design,we prepare MXene/WPU-based EMI shielding coatings that are suitable to a variety of substrates,MXene/ST-Zn O/WPU nanocomposite films,and MXene/PP nanocomposites with outstanding EMI shielding performances.The main work is as follows:(1)In order to solve the problems of poor adhesion and environmental stability of MXene,water-based conductive inks with stable dispersion based on MXene/WPU are obtained by combing WPU with strong adhesion with MXene on the basis of the good interface compatibility between the nanosheets and matrix,and can be applied to polyimide(PI)membrane,cotton textile,melamine sponge,and other substrates as EMI shielding coatings.WPU can not only enhance the adhesion fastness of MXene to the substrate,but also protect the conductive network of MXene,and improve its environmental stability.MXene/WPU coatings not only have a satisfactory adhesion stability to PI membrane substrate,with an adhesive force reaching ISO level 1,which can meet most commercial requirements,but also have both an average EMI shielding effectiveness(SE)of up to 40.3 d B in the X-band at a low coating thickness of 20μm,and a good environmental stability,with a decline rate of no more than 7%for EMI SE after the treatments by ultrasonic shock and acid,alkali,and organic solvents.Moreover,the coatings with cotton textile and melamine sponge as substrates both show good EMI shielding performances,with average SE of 39.7 d B and 60 d B,respectively in the X-band.The MXene/WPU coatings endow a variety of insulating substrates with excellent EMI shielding performances by a simple and efficient process.(2)In view of the difficulty of combining excellent EMI shielding performance with low thickness for polymer nanocomposites when MXene nanosheets are randomly dispersed in WPU matrix,on the basis of the three-dimensional skeletons and volume-exclusion effects of silane-modified tetra-needle Zn O whiskers(ST-Zn O),MXene/ST-Zn O/WPU(MTW)nanocomposite films are prepared by coating ST-Zn O with MXene nanosheets,followed by compounding with WPU.Compared with MXene/WPU(MW)nanocomposite films,the MTW counterparts with the same MXene mass content and sample thickness have higher conductivity and EMI shielding properties.The MTW nanocomposite film has not only an ultrahigh conductivity of 4.8×10~4 S/m,but also an excellent EMI shielding performance of more than 70 d B in the X-band at a low thickness of 0.1 mm.In addition,the MTW nanocomposite films exhibit excellent Joule heating performances with an equilibrium temperature of 113℃at a low driving voltage of 3 V.(3)In view of the difficulty of dispersing MXene nanosheets in hydrophobic polymers,the hierarchical porous PP textiles are first activated by oxygen plasma and PEI,then coated with MXene nanosheets,and finally converted into dense MXene/PP nanocomposites by the vacuum assisted hot pressing process.PP fibers are molten into polymer matrix to stabilize the interconnected MXene conductive networks and play a role of volume-exclusion.The MXene/PP nanocomposites show not only an ultralow percolation threshold of 0.027 vol%,but also a high conductivity of 4.4×10~2 S/m and an excellent EMI shielding performance of above 60 d B in the X-band at a low MXene content 2.12 vol%.This work provides a new method for preparing MXene/polymer nanocomposites with a low percolation threshold.