| As the service environment of composites in the aerospace field changes,the integration of structure and function has become the necessity of the development of carbon fiber reinforced composites.The interphase,as the"bridge"of stress and energy transfer,determines the efficiency of structural and functional properties of carbon fiber composites.Therefore,atablishing the interphase with integrated structure and function has become a research hotspot.Therefore,the method of constructing the interphase of carbon fiber composites by metal-organic framework(MOF)assembly and metal-organic framework/carboxylated multi-wall carbon nanotubes(MOF/MWNT)hierarchical assembly was proposed and the performance and mechanism of interface reinforcement and electromagnetic shielding of MOF assembly layer and MOF/MWNT hybrid assembly layer was researched.Through the design and regulation of interphase with integrated structure and function,the dual improvement interface and electromagnetic shielding performance of CFRP was achieved.(1)Metal-organic framework materials based on naphthalenediimide ligand was prepared,and MOF was constructed on the surface of carbon fiber by secondary growth method to acquire MOF@CF.Compared with CF-desized,surface chemical activity and roughness of MOF@CF were increased.The MOF assembled layer was constructed by randomly distributed"jujube core"structures on MOF@CF surface.The MOF assembly mechanism was proposed as follow:after crystal seeds of MOF were constructed on the surface of carbon fiber,NDI ligands and copper ions were aggregated to carbon fiber surface and assembled by coordination.Meanwhile,MOF recognized substrate under the influence ofπ-πinteraction between ligand and sp~2-hybridization domain of carbon fiber substrate and assembled.(2)CF-desized surface was treated step by step with MWNT sizing agent,solution of crystal seed of MOF and assembly solution of MOF for preparing MWNT@CF and MOF/MWNT@CF.Compared with MWNT@CF,the surface chemical activity and roughness of MOF@CF were increased.On the surface of MOF/MWNT@CF,MOF and MWNT were connected and interpenetrated to form MOF/MWNT hybrid assembly layer.The mechanism of MOF/MWNT hierarchical assembly was proposed:"the MWNT network of primary construction"was used as the template for nucleation and assembly of MOF;Crystal seed of MOF of“secondary construction"provides the nucleation site for subsequent assembly,and induces ligand NDI and copper ions to aggregate and assemble on the substrate;The coordination of carboxyl group of on the substrate and sp~2 hybridization domain of CF and MWNT promote the regular arrangement of ligand NDI and copper ions,and make MOF assembly on the surface of carbon fiber to form"tertiary construction".(3)The bundle,monofilament and unidirectional composites of CF-desized,MOF@CF,MWNT@CF and MOF/MWNT@CF were prepared to evaluate the interfacial properties and fracture morphology.The changes of interphase modulus and C element of four kinds of composites were compared by f-AFM and EDS,and the electromagnetic shielding properties of the four composites were evaluated by vector network analyzer.Compared with CF-desized and MWNT@CF composites,TFBT,ILSS and IFSS strength of MOF@CF and MOF/MWNT@CF were improved.The mechanisms of interface enhancement were proposed:MOF assembly structure acted as"rivet"to improve the interface bonding and increase the absorbed failure energy.MOF/MWNT hybrid assembly layers combined"rivet"and"armor"to improve the interface bonding,increase the crack propagation path and absorb failure energy.In addition,compared with CF-desized and MWNT@CF,the electromagnetic shielding efficiency of MOF@CF and MOF/MWNT@CF composite was improved,due to the MOF assembly layer increased conductivity loss and interface polarization,and the MOF/MWNT hybrid assembly layer further increases conductivity loss structure,interface polarization sites and multiple reflections. |
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