Multifunctional Aramid Nanofiber/Carbon Nanotube Hybrid Aerogel Films
    With the development of the times and the progress of science and technology, 5g era has come. The application of electromagnetic wave in civil and communication systems is more and more extensive, and the potential harm to human health is also increasing, the development of functional shielding materials is also accelerating at the same time. Lightweight, robust, and ultra-flexible multifunctional shielding materials are highly desirable to meet the technological demands of current society though great progress has been made in basic research. To overcome these challenges, researcher Zhang Xuetong from Suzhou Institute of Nano-Tech and Nano-Bionic, Chinese Academy of Sciences (SINANO), in collaboration with Professor Chen Yongping of Hainan University, prepared ANF/CNT hybrid aerogel films with excellent mechanical and electrical properties by compounding high strength aramid nanofibers (ANF) and electricity / thermal conductive carbon nanotubes (CNT), then hydrophobic FC-ANF/CNT aerogel films were obtained by supplemented with hydrophobic fluorocarbon (FC) resin modification. Compared with the traditional membrane shielding materials, the aerogel films have many advantages: (1) low density (0.043g/cm3), high porosity and good flexibility; (2) excellent hydrophobic properties, which can be used in wet environment; (3) satisfactory electricity / thermal conductive and electric heating properties; (4) better electromagnetic shielding performance and electromagnetic shielding performance.
Preparation process
   
Figure 1. Schematic of the Fabrication and Structural Composition of the FC-ANF/CNT Hybrid Aerogel Film and Its Multifunctionality (Self-Cleaning, Joule Heating, and EMI Shielding).
    Fluorocarbon resin reduces the surface energy as a hydrophobic coating, and ANFs and CNTs provide surface roughness and reduce the liquid-solid contact area as the construction units of aerogel films resulting in good hydrophobicity (137 degrees). In addition, the phenomenon that the film remains not wetted by hot water at 80 ℃ is due to the integrity of FC coating at hot water temperature to support the liquid with low surface tension and prevent it from wetting.
Figure 2. Characterization of hydrophobicity of FC-ANF/CNT aerogel film.
    The electrical conductivities of FC-ANF/CNT aerogel films rapidly increased with the increase of CNT content whereas the conductivity further increased and reached 230 S·m−1 with 40 wt % CNT loading. The flexible, robust FC-ANF/CNT hybrid aerogel films can be used as electric heaters based on the Joule heating effect for personal thermal management. A voltage of 5 V yielded a saturated temperature of 52.6 °C which can be needed for keeping warm. The low driving voltage not only guarantees the energy conservation and the safety to humans (less than 36 V) but also allows the heater to be powered by a portable battery or a supercapacitor. Besides, the FC-ANF/CNT aerogel film also has heating stability and durability.
Figure3. Joule heating effect of FC-ANF/CNT aerogel film.
    The FC-ANF/CNT aerogel films with a 3D porous network structure and high electrical conductivity are expected to show excellent EMI shielding performance. The shielding performance reaching the maximum value of 54.4 dB (99.999% shielding) with 40 wt % CNT content at a thickness of 568 μm. Theoretical analysis shows that the attenuation of the incoming electromagnetic wave originates from the conductance loss and the interfacial polarization loss in the three-dimensional conductive network of aerogels, while the porous structure of aerogels further increases the multiple scattering paths of the waves, thus enhancing the attenuation ability of the materials to the electromagnetic waves. The electromagnetic shielding efficiency of the aerogel films is as high as 33528.3 dB. cm2. G-1 due to the light and thin characteristics, which is higher than that of traditional carbon based, metal based or conductive polymer based shielding materials.
Figure 4. EMI shielding performance of FC-ANF/CNT aerogel films.
    CNT aerogel film will broaden application prospects in intelligent films, wearable electronics, EMI shielding clothing, and personal thermal management systems. This study is entitled " Multifunctional Aramid Nanofiber/Carbon Nanotube Hybrid Aerogel Films " and published in ACS Nano (DOI: 10.1021/acsnano.9b07459). 
Master student Hu Peiying (co-trained by Hainan University and SINANO) and postdoctoral Lv Jing (SINANO) are the co-first authors of this paper. Researcher Zhang Xuetong from SINANO and Professor Chen Yongping from Hainan University are the co-corresponding authors of this paper.

LINK: Multifunctional Aramid Nanofiber/Carbon Nanotube Hybrid Aerogel Films(ACS Nano, 2019, DOI:10.1021/acsnano.9b07459)