| With the rapid development of microelectronics industry,significant problems related to electromagnetic compatibility,electromagnetic interference and electromagnetic pollution,are becoming increasingly prominent.Therefore,the research in electromagnetic interference(EMI)shielding materials is attracting great attention from academia and industrial circles.Especially in special fields such as aerospace,it is of great scientific significance and application value to develop carbon-based EMI shielding materials with both lightweight and high-efficiency shielding effectiveness(SE).Graphene,with excellent electrical conductivity and high aspect ratio,is often used as an ideal nanoscale functional material in the preparation of polymer or bio-based carbon composites for fabricating low-density and high-performance carbon-based EMI shields.So far,although great progress has been made,there are still many challenges about how to meet the new expectations on EMI shields for all-weather outdoor electronic equipment,how to adjust the EMI SE by special structure designs.To solve these issues,some material system selection and structural design have been conducted in this thesis,and the innovative achievements are as following:(1)Super-hydrophobic porous polymer composites with excellent EMI shielding and self-cleaning function were fabricated by poly(vinylidene fluoride)(PVDF)as low-surface-energy matrix as well as carbon nanotubes(CNTs)and graphene as hybrid filler through a modified water vapor-induced phase separation process with non-woven fabric as a template.The resultant materials exhibited not only porous microstructure composed of assemble spherulites,but also multi-scaled raspy super-hydrophobic surfaces,with possessed high shielding effectiveness up to 62.7 dB and water contact angle high as 155.4°±2.7°.Moreover,they showed good performance of stability under ultraviolet irradiation as well.This simple and reproducible fabrication technique together with UV-resistant super-hydrophobicity and excellent EMI shielding would make such materials possible for practical lightweight self-cleaning EMI shields.(2)Natural cotton was selected as green and renewable carbon sources to fabricate novel carbon networks composing of numerous unique hollow carbon fibers with outstanding EMI SE by pyrolysis.Then,the combination of carbon fibers with graphene through constructing a sandwich configuration,where graphene sheets were dispersed inhomogeneously on both sides of carbon networks,was further developed and carbon composite networks with ultrathin skin layers of graphene film in thickness of only~2?m possessed higher SE total of 48.5~87.0 dB than that(33.7~55.6 dB)of pure carbon networks under the same sample thickness of 0.3~0.7 mm.The SE increment of 26~41%was also observed in the sandwiched samples compared to the counterparts with homogeneous graphene dispersion,demonstrating a very promising configuration for the significant SE enhancement.(3)Novel straw-derived hollow porous carbon-tube arrays(SCAs)were fabricated through direct carbonization of agricultural waste wheat straw followed by orderly assembly.The resultant SCAs with increased SC diameter of 1.7~3.3 mm showed not only low apparent density of 72~33 mg/cm~3 due to the presence of arrayed hollow macrostructure,but also high EMI SE of 57.7~44.0 dB coming from both the strong EM reflection and conductive dissipation,as well as hierarchical internal multiple reflections.After the further construction of ultralight graphene aerogel(GA)in their hollow interior,the GA/SCAs with slightly increased density of only 78~39 mg/cm~3exhibited obvious SE enhancement of 66.1~70.6 dB compared to those of neat SCAs.In addition,the performance comparison between our SCAs and other previously reported carbon foams also revealed the more advanced configuration of hollow porous carbon-tube array for lightweight and high-performance EMI shielding application. |
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