| The wide application of electronic information technology improves the convenience of people’s lives,but the serious problems of electromagnetic pollution,which threatens the operation of precision equipment,information security and human health,puts forward new requirements for the development of efficient electromagnetic interference shielding materials.Metal electromagnetic interference shielding material has excellent electromagnetic interference shielding performance,but due to its high density,poor corrosion resistance,difficult processing and other disadvantages limit its wide application.Compared to metal materials,polymer-based electromagnetic interference shielding materials have low density,chemical corrosion resistance,easy processing and adjustability of electromagnetic interference shielding properties,which has attracted a lot of attention from researchers.In this paper,polyimide(PI)was used to construct aerogel and reinforce it by cation-π crosslinking structure.Based on this,MXene nanosheets are loaded on the aerogel pore wall to give the composite aerogel electromagnetic interference shielding properties.Finally,by constructing anisotropic aerogel material,the electromagnetic interference shielding performance in vertical freezing direction is further improved.Designed to build lightweight,high-strength,high-efficiency electromagnetic interference shielding aerogel materials.(1)Firstly,with 4,4’-oxy bisbenzenam ine(ODA)and 3,3’,4,4’Benzophenonetetracarboxylic dianhydride(BTDA)is a monomer,using 2-(4aminophenyl)-5-Amino benzimidazole(APBIA)introducing electron-rich imidazole rings into molecular chains,preparation of precursor polyamide aqueous solution using triethylamine as dissolving aid,then the PI aerogel was prepared by freeze drying combined with thermal imidization,the cation-π action is introduced to crosslink the molecular chain to enhance the aerogel skeleton structure.The results show that the cation-π crosslinking structure is introduced.Increases the structural stability of aerogels.Compared with Pure PI,PI aerogel with 30%Cu2+ addition volume shrinkage decreased from 63.8%to 56.1%.The density is reduced from 0.103 g/cm3 to 0.092 g/cm3.At the same time,the mechanical strength of the aerogel has been significantly improved.The Young’s modulus increased from 3.6 MPa to 5.9 MP a and the yield strength increased from 0.2 MPa to 0.4 MPa.(2)Secondly,with PI aerogel as the substrate material,the MXene nanosheets are loaded on the aerogel pore wall by immersion method,which gives them electromagnetic interference shielding properties.The results show that the load of MXene nanosheets can form a layer of MXene film with large folds on the microstructure surface of the aerogel.Because the imidazole group on the PI aerogel molecular chain can perform cation-π action with the Ti atoms in the MXene nanosheet,improved interfacial forces between MXene nanosheets and PI aerogels So that the MXene nanosheets load five layers,MXene film can still be better coated on PI aerogel surface.In addition,as the number of load layers of MXene nanosheets increases,the conductivity and electromagnetic interference shielding efficiency of MXene@PI composite aerogel increase.When the MXene nanosheets load five layers,MXene@PI-5 composite aerogel has a conductivity of 153 S/m,electromagnetic interference shielding performance up to 29 dB,Meet the performance requirements of commercial electromagnetic interference shielding materials.(3)Finally,the structure of MXene@PI composite aerogel is regulated by directional freezing technology,giving it anisotropy.The results showed that,unlike the porous structures exhibited by random freezing aerogels in all directions,the anisotropic MXene@PI composite aerogels were honeycomb porous in the parallel freezing direction and ductal in the vertical freezing direction.In addition,under the same MXene nanosheet load layer,the conductivity and electromagnetic interference shielding efficiency of vertical freezing direction are much greater than that of parallel freezing direction and random freezing composite aerogel.When the MXene nanosheets load five layers,anisotropic MXene@PI-5 composite aerogel conductivity and electromagnetic interference shielding efficiency in vertical freezing direction are 182 S/m and 62.7 dB respectively,much greater than parallel direction(114 S/m and 24.3 dB)and random frozen composite aerogels(153 S/m and 29 dB). |
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