Research On Structure Regulation And Electromagnetic Shielding Performance Of MXene-based Nanofiber Membrane

Two-dimensional transition metal carbides（MXene）have good hydrophilicity and excellent electrical conductivity,and have broad application prospects in the field of electromagnetic shielding.However,pure MXene film has poor mechanical properties and poor structural stability,which is difficult to meet the practical application of electromagnetic shielding materials.Therefore,in our study,based on the layer-by-layer assembly strategy,a light-weight and flexible MXene-based conductive composite film was constructed by using polyacrylonitrile（PAN）nanofiber film as the substrate by compounding with MXene.On the basis of optimizing the synthesis process of MXene nanosheet,sandwich structure,double conductive layer structure and double scale structure were constructed by modifying PDMS（polydimethylsiloxane）on the surface of composite film,modifying PPy（polypyrrole）inside fiber and doping PPy inside the nanosheet to gradually improve the electromagnetic shielding performance（EMI SE）of composite film.The practical application of MXene-based fiber composite film in the field of electromagnetic shielding is realized in the future.Meanwhile,the problems of uncontrollable thickness of EMI shielding material,low shielding efficiency and difficult dispersion of conductive filler are solved.The specific research contents are as follows:（1）The PAN nanofiber film was used as the substrate,and the MXene-based composite film was constructed by hydrophilic modification of polydopamine（PDA）and dip-coating process.On the basis of optimizing the synthesis process of multilayer MXene nanosheets,the effects of MXene dip-coating times on the morphology,tensile,electrical conductivity and EMI shielding properties of the composite films were investigated.The results shown that when the number of dip-coating times was 4,the thickness of the composite film was 45μm,the tensile strength was 101.06 MPa,the EMI SE value was 31.75 d B,the EMI shielding efficiency was 99.93%,and the SSE/t value was 4864.44 d B cm²g^-1.It was proved that the MXene-based conductive composite film with certain mechanical strength could be prepared by the composite of MXene and PAN nanofiber film,which effectively solved the problem of poor mechanical properties of pure MXene film.（2）To improve the stability and EMI shielding performance of MXene-based conductive composite film,the layered optimization of MXene nanosheets was carried out,and the surface of the composite film was hydrophobic modified by silicon-containing hydrophobic agent（PDMS）to improve the structural stability of the conductive layer,and the sandwich structure of MXene based conductive composite film（PNP@MXene film）was constructed.The effects of hydrophobic modification on the structural stability,electrical conductivity and EMI shielding performance of composite films were investigated.The thickness of the composite film was 29μm,the surface contact angle was 125.49°,the EMI SE and SSE/t value was 28.82 d B and12422.41 d B cm²g^-1,which could shield 99.87%of electromagnetic waves.The results shown that the coupling of different functional layers realized the high-performance EMI shielding of MXene-based composite films under ultra-thin thickness,which provided a research idea for the structural stability design of MXene-based composite films.（3）In order to further improve EMI shielding effectiveness,the PPy conductive core-shell structure was constructed on the fiber film by low-temperature interface polymerization process to realize the internal fiber functionalization,and the MXene-based conductive composite film with double conductive layer structure was constructed by sequential composite MXene conductive layer.The effects of PPy modification and hydrophobic modification on the EMI shielding properties of MXene-based composite films were explored,and the synergistic shielding mechanism of PPy-modified MXene-based composite films was studied.The thickness of the final composite film was 45μm,the surface contact angle was 124.99°,the EMI SE and SSE/t values were 37.71d B and 14779.90 d B cm²g^-1,which could shield 99.98%of electromagnetic waves.（4）In order to further improve EMI shielding effectiveness and structural stability of conductive layer,MXene nanosheets assembled inside PPy nanoparticles were combined with PAN film by filtration technology.And Ni-Co（NC）microspheres and PDMS were combined to achieve hydrophobic modification on the surface of the composite film,and then MXene-based composite film with dual scale structure was constructed.On the basis of determining the optimal process for assembling MXene nanosheets inside pyrrole,the effect of suction filtration process on the structure and EMI shielding performance of the composite film was studied.The synergistic hydrophobic mechanism between NC microspheres and PDMS was explored,and the shielding mechanism of the composite film with dual scale structure was explained.The surface contact angle of the composite film was 138.99°,and the EMI SE value reached 38.73 d B,which could effectively shield 99.99%of the electromagnetic wave.Meanwhile,the combination of the internal assembly of MXene in PPy and the suction filtration process was expected to broaden the industrial application of MXene-based conductive materials,which can be flexibly used in wearable electronic devices and shielding devices.（5）In order to deeply reveal the inside and outside shielding mechanism of the MXene-based composite film,the electromagnetic dissipation properties of pure MXene nanosheets and PPy-modified MXene nanosheets with different contents were comparatively studied,and the attenuation process and shielding mechanism of electromagnetic waves in MXene layer were proved.The electromagnetic field simulation（CST）model of MXene-based composite film was established to study the influence of surface hydrophobic modification and conductive functional layer modification on the changes of electric field intensity and energy loss in the electromagnetic wave shielding process,and it was verified that electromagnetic radiation pollution can be effectively shielded by regulating the functional layer.It provided a theoretical basis for the design of lightweight,flexible and high-performance MXene-based composite film.