| The explosive development of telecommunication technology and the innovation of electronic equipment have attracted people’s attention to the problem of electromagnetic radiation.Electromagnetic interference(EMI)not only affects the normal operation of equipment,but also threatens people’s health.One of the most effective ways to solve electromagnetic pollution is to prepare electromagnetic shielding materials with ultra-thin,light weight,strong attenuation ability and good mechanical stability.Up to now,new two-dimensional(2D)MXene materials have shown great potential in the field of electromagnetic shielding due to their excellent electrical conductivity,unique layered structure,adjustable surface chemistry and easy solution processability.However,single-component MXene based shielding materials have poor mechanical strength,not resistance to oxidation and single function,which seriously limit their application fields.In this paper,flexible and multifunctional MXene-based electromagnetic shielding films are constructed through component regulation and structural design,and the influence mechanism of component synergism,layered structure optimization and prefabricated conductive network structure on their electrical conductivity,mechanical strength and electromagnetic attenuation are studied.The specific research contents and results are as follows:(1)Based on the synergistic enhancement effect between materials with different dimensions,MXene/SWNTs films with nacre-like structure are prepared by vacuum-assisted filtration method.The doping of SWNTs with high aspect ratio reduces the contact resistance between MXene nanosheets,which improves the conductivity and electromagnetic shielding properties of composite film.The interpenetrating network structure and nacre-like structure improve the mechanical strength of MXene,which endows the composite film with flexible property.By optimizing the ratio of MXene to SWNTs,the tensile strength reaches 41.7 MPa,the electrical conductivity is 1851.9S/cm,and the electromagnetic shielding effectiveness(EMI SE)is 78.9 d B.When the thickness is 296μm,the EMI SE is as high as 108.1 d B.At the same time,the composite film maintains excellent stability in extreme conditions,such as ultrasonic treatment,acid/alkali corrosion,high/low temperature treatment,and combustion treatment.In addition,the composite film exhibits good photothermal conversion performance to extends its application field,and its surface temperature reaches 66.2 ~℃ under the light intensity of 100 m W/cm~2.(2)Inspired by the isolation structure and nacre structure,MXene@CNF films with alternating multilayer structure are prepared by alternating vacuum-assisted filtration method.The independently distributed MXene layer facilitates electron transmission and improves the conductivity and electromagnetic shielding performance of composite film.The alternately ordered CNF layers act as skeleton support to ensure the structural stability of MXene,improve the mechanical strength of composite film and endow it good flexibility.By optimizing the number of MXene layer,the tensile strength,electrical conductivity and EMI SE of the alternating multilayer film are 112.5MPa,143 S/m and 39.6 d B,respectively.When MXene content is 80 wt%,the EMI SE reaches 55.5d B.In addition,the composite film exhibits excellent Joule heating property to ensure the stability of polymer in low temperatures,and its surface temperatures can reach more than 100 ~℃ in 10 s at a voltage of 6 V.(3)The asymmetric sandwich MXene@Ag NW@CNF film is prepared by layer-by-layer vacuum-assisted filtration method.The independent distribution of MXene and Ag NW core layer improves the electron and phonon transfer,which makes the composite film have excellent electrical conductivity,electromagnetic shielding and thermal conductivity.The CNF skin layer ensures the stability of core layer structure,improves the mechanical strength of composite film,and endows it with excellent bending resistance.Through the optimization of component ratio,the tensile strength of asymmetric sandwich film is 118 MPa,the electrical conductivity is up to 37378S/m,the EMI SE is 55.9 d B,and the in-plane thermal conductivity is up to 15.53 W/m K.When the conductive filler is 80 wt%,the EMI SE reaches 75.8 d B.In addition,the composite film shows excellent photothermal conversion performance,and its surface temperature reaches 83.6 ~℃ at the light intensity of 100 m W/cm~2.(4)MXene/PEDOT:PSS@ANF film with Janus double-layer structure is prepared by the two-step vacuum-assisted filtration method.The independently distributed MXene/PEDOT:PSS layer improves conductivity and electromagnetic shielding performance of composite film.Among them,the doping of PEDOT:PSS improves the interfacial bonding strength of MXene layer and ANF layer,and endows the conductive layer with good hydrophobic performance(122.2~o),which improves the water erosion resistance of conductive layer.The mechanical support of ANF layer and the hydrogen bonding force between conductive layer and substrate significantly improve the mechanical strength and bending resistance of composite films.When the mass ratio of MXene to PEDOT:PSS is 7:1,the tensile strength and tensile strain of Janus films are as high as 155.9 MPa and 20%,respectively,the sheet resistance is as low as 2.18Ω/sq,and the EMI SE is 45.1d B.When the film thickness is 47μm,the EMI SE reaches63.7 d B.In addition,the composite film exhibits excellent Joule heating property and photothermal conversion capability,broadening their application range.The surfac temperature can be as high as 382 ~℃ when the applied voltage is 4 V.When the light intensity is 100 m W/cm~2,its surface temperature is 59.6 ~℃.(5)The construction of prefabricated conductive network structure is a feasible method to prepare high-efficient transparent electromagnetic shielding films.Transparent MXene/Ag NW-PVA shielding film is prepared by spraying,spining and hot pressing.The synergistic effect of 1D/2D conductive fillers and the construction of prefabricated conductive network reduce the contact resistance of MXene,which improve the conductivity and electromagnetic shielding performance of transparent film,and make it show good light transmittance.The interfacial bonding force between conductive network and PVA substrate is enhanced by the fixation and transfer of PVA solution,which improves the scratch resistance and bending resistance of composite film.By optimizing the surface density of MXene and Ag NW,the sheet resistance of transparent film is as low as 18.3Ω/sq,and the light transmittance remains 52.3%.When the thickness is only 10μm,the transparent film shows good EMI SE(more than30 d B)in both X-band and K-band.In addition,the transparent film shows excellent Joule heating performance and stability,and the surface temperature reached 118 ~℃ in only 10 s when the applied voltage is 5 V. |
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