Progress in the preparation of new carbon-based electromagnetic shielding materials for urban environments

[ Instrument R & D of Instrument Network ] The rapid development of advanced electronic equipment and wireless communication technology has brought great convenience to people ’s lives, but it also produced electromagnetic radiation pollution problems that cannot be ignored, which will not only seriously interfere with the normality of surrounding electronic components Operation, reduce information security and communication quality, and will harm human health. With the rapid increase in the number of new-generation highly integrated, high-power and high-frequency electronic devices led by the 5G era, the problems of electromagnetic interference and radiation have become increasingly prominent.

The development of high-performance electromagnetic shielding materials is an important means to suppress electromagnetic interference and pollution, and is also an indispensable component to ensure the normal operation of electronic equipment. In addition to the high shielding performance of electromagnetic shielding materials, electronic products and devices that are continuously miniaturized, lightweight, flexible, and intelligent also put forward requirements for characteristics such as light weight, thin layer, and flexibility. Traditional metal shielding materials have been difficult to meet the new expectations of material development due to their high density, corrosion resistance, and poor toughness. The development of new shielding materials that replace traditional metals is imperative.

Carbon-based shielding materials made of graphene, carbon nanotubes, carbon fiber, activated carbon, etc. have the advantages of light weight, corrosion resistance, adjustable performance, etc. and are favored by researchers. Gel materials and carbon film materials. However, in order to obtain excellent electromagnetic shielding effectiveness, the thickness of polymer composite materials and aerogel materials often reaches millimeters or even centimeters, and the high-temperature heat-treated carbon film materials have poor mechanical properties and insufficient flexibility. The above problems seriously hinder practical applications . Therefore, the development of new electromagnetic shielding materials with light weight, small thickness, good flexibility, and superior shielding performance still faces considerable challenges.

Based on this, the Clean Energy Technology and Carbon Materials Research Group of the Institute of Urban Environment, Chinese Academy of Sciences (Wang Yin team) used graphene oxide nanosheet self-assembled thin film as a precursor, and reduced the foam in the film by the method of reduction and limited foaming. Controllable construction of uniformly layered porous structure and preparation of flexible porous graphene membrane. The porous structure formed by the strong connection between the separated graphene sheets can effectively realize the load transmission, giving the graphene film excellent folding resilience and flexibility; the folding elasticity is treated at high temperature and liquid nitrogen (-196 ℃) ultra-low temperature and No change after folding in the second cycle. In addition, the porous structure increases the number of multiple reflections of electromagnetic waves in the film, effectively improving the material's absorption loss and shielding performance of electromagnetic waves. Therefore, the prepared porous graphene film still has ultra-high shielding effectiveness (~ 63.0 dB, shielding 99.99995% of incident electromagnetic waves) when the thickness is less than 200 μm, which is much higher than the application level of 20 dB and the density is only 48 mg / cm3, normalized specific shielding effectiveness SSE / t up to 49750 dB cm2 / g. This work realizes the controllable preparation of electromagnetic shielding materials that are light, thin, flexible, and excellent in shielding effectiveness. The new materials have good application prospects in electromagnetic shielding in the fields of flexible electronic devices, wearable / foldable electronic products, and so on.

Related achievements were published in Carbon, 2020, 158, 728-737 with the title of Controllable fabrication of elastomeric and porous graphene films with superior foldable behavior and excellent electromagnetic interference shielding performance. The research was funded by a major project on Sino-Japanese international cooperation, a pilot project in Fujian Province, and the National Natural Science Foundation of China.