| Three-dimensional porous electromagnetic shielding composites have many advantages, such as low density, high specific surface area, porosity, strong weather resistance, high loading of conductive filler, which is highly favored by researchers. Especially the research of materials with the matrix of refractory polymer nanofibers is a hotspot. But limited by the preparation process of refractory polymer nanofibers, such nanofiber substrate has not been widely used in electromagnetic shielding composite materials.In this paper, high-performance polymer Poly{2,6-dimidazo[4,5-b:4’,5’-e]pyridinylene-1,4(2,5-dihydroxy)Phenylene}(PIPD) was used as matrix. PIPD nanofibers were prepared respectively by conventional alkaline degradation and swellingultrasonic peeling method studied by research group independently and draw optimal nanofiber optimum and optimum parameter. Further, high conductivity PIPD/Au threedimensional porous composite material was prepared by self-assemble, and the structure and properties of each step of the obtained materials were characterized and researched.Traditional alkaline degradation was tried to prepare PIPD nanofibers. Results showed that formation of PIPD nanofibers was poor, which couldn’t be used as the matrix of composites. The method of swelling-ultrasonic peeling was used to prepared PIPD nanofibers, the best parameter is: PIPD spun fibers were swelled in DMSO at 155℃ for 6h, and then sonicated at room temperature for 96 h. Then PIPD nanofibers with uniform structure and large aspect ratio were obtained.Preparing macromolecular initiator by the reaction of 2-bromo-propionyl bromide and PIPD nanofibers, then the macroinitiator was used to initiate polymerization of DMDAAC on PIPD nanofibers’ surface to graft PDDA. Studies have shown that after the graft modified, PIPD nanofibers’ surface is positively charged(~ 40Mv), and well waterdispersible. By self-assembling the modified nanofibers and gold nanoparticles prepared by the method of Frens formed PIPD/Au composite with three-dimensional porous structure. PIPD/Au composite material can withstand temperatures of 500 ℃. The maximum density of the composite is only 1.056g/cm3. The tensile strength can be achieved 22.59 MPa. PIPD/Au composite is lightweight, heat-resistant, high porosity, owning excellent mechanical properties and other advantages.Using conductivity test instrument and electromagnetic shielding performance test instrument characterized performances of PIPD/Au nanoiber composite material. The results showed that the material has excellent electrical conductivity which is up to 15890S·cm-1, close to the conductivity of metallic aluminum. Further, after the heat treatment and pressure treatment, the conductivity of the material is further increased to 18300S·cm-1 and 22240S·cm-1. The composite has excellent electromagnetic shielding performance. Shielding effectiveness of single-layer composite with the thickness of 20μm is up to 64.9dB. After laminating four PIPD/Au composites together, shielding effectiveness is up to 93 d B, exhibiting excellent electromagnetic shielding effectiveness. The shielding mechanism of PIPD/Au nanofiber composites is that the porous structure of the composites makes electromagnetic signal refract and reflect repeatedly, reducing the electromagnetic signal transmission rate greatly and achieving the shielding of electromagnetic interference signal. |
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