| With the wide application of wearable electronic devices,efficient and flexible electromagnetic shielding materials have received extensive attention.Traditional metals or metal alloys have electromagnetic shielding effectiveness(SE)higher than60 d B due to their high electrical conductivity and small skin depth,but they possess the drawbacks of high density,poor flexibility,and chemical corrosion resistance,which hinder their wide application to a certain extent.In this dissertation,Polyimide fiber(PIF),which is resistant to extreme high and low temperature,high mechanical strength,chemical corrosion and good flexibility,is used as the matrix,and a stable and efficient conductive network is constructed by compounding with conductive filler to obtain a new flexible conductive composite membrane,and its performance in electromagnetic shielding and environmental tolerance is systematically studied,providing a theoretical basis for the design and preparation of new high-efficiency flexible electromagnetic shielding materials.The main research results are as follows:(1)PIF/MXene flexible conductive composite film with a "rebar-brick-cement" layered structure was prepared using the vacuum-assisted filtration and thermal imidization technique.As a binder and dispersant,the water-soluble polyimide precursor polyamide acid(PAA)not only ensures the uniform dispersion of MXene in PIF matrix,but also results in good bond enhancement between PIF and MXene through thermal imidization.As a result,a conductive composite film with excellent mechanical strength and high conductivity(3787.9 S/m)was obtained.However,good electrical conductivity can usually lead to a poor impedance matching with free space,resulting in strong reflection of the incident electromagnetic wave(8.2-12.4 GHz)from the surface of the composite conductive film.Besides,the electromagnetic waves entered the interior of the materials can be further attenuated by ohmic conduction loss,interface/dipole polarization loss and multiple scattering.Overall,the prepared PIF/MXene flexible conductive composite film shows an excellent electromagnetic shielding performance dominated by reflection mechanism(SE= 49.9d B).(2)PIF membrane(PIFM)/silver nanoparticles(Ag NPs)/styrene-ethylene-butylenestyrene block copolymer(SEBS)flexible conductive composite films were prepared by dip coating-reduction process.SEBS was used as a binder to immobilize Ag NPs in the PIF fiber network to build a stable and efficient conductive network(S=32051.3S/m).Meanwhile,the low surface energy of SEBS and the rough microstructure formed by Ag NPs aggregation endow the film with excellent self-cleaning ability.The results indicate that the Ag NPs loading and film thickness will affect reflection loss,ohmic conduction loss,interface polarization loss and multiple scattering of the conductive film towards the incident electromagnetic waves,achieving the tunable electromagnetic shielding performance.Meanwhile,its good electrical conductivity also enables it to exhibit excellent electromagnetic shielding performance(SE=58.2 d B)dominated by the reflection mechanism.(3)Based on the excellent physical properties of PIF and the good interface adhesion between conductive filler and PIF matrix,the prepared two PIF composite conductive films can still maintain good electromagnetic shielding efficiency in various extreme harsh environments,showing excellent stability and durability.In addition,the conductive composite film also shows rapid,durable and stable joule heating performance,demonstrating good application potential in personal thermal management and outdoor deicing,and also broadening its usefulness as a wearable electromagnetic protection material to a certain extent. |
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