Lightweight and Anisotropic Porous MWCNT/WPU Composites for Ultrahigh Performance Electromagnetic Interference Shielding

Abstract

303wileyonlinelibrary.com EMI SE reveals the ability of materials to attenuate electromagnetic waves and is generally expressed in decibel (dB). [ 11,12 ] For the applications that need lightweight shielding materials, however, the specifi c SE (SSE), which is defi ned as SE divided by mass density, is also a crucial criterion. [ 8 ] In porous CPCs, the air bubbles arise in the material and thus the mass density is reduced. If conductive networks are formed therein by the electric fi llers with large aspect ratios, such as carbon fi bers (CFs), carbon nanotubes (CNTs), or graphene layers, it will lead to high electrical conductivity in addition to the low density, [ 9,13,14 ] which are benefi cial to higheffi ciency EMI shielding. [ 10,[15][16][17][18][19][20] In consideration of that, Yang et al. reported porous CPC-based EMI shielding material of 15 wt% carbon nanofi ber/ polystyrene (PS) composite foams with SE ≈19 dB in the frequency range of 8.2-12.4 GHz (X-band), [ 16 ] and 7 wt% CNT/PS porous composite fabricated with the aid of chemical blowing agents obtained SE ≈19 dB at a density of 0.56 g cm −3 .[ 17 ] Those porous CPCs indicate higher utilization of materials than typical metal-based shields, as SSE is 33.1 dB cm 3 g −1 for 7 wt% CNT/PS composite foams [ 17 ] and 16-25 dB cm 3 g −1 for 5 wt% porous graphene/polymethylmethacrylate (PMMA) composites, [ 18 ] higher than that of solid copper ≈10 dB cm 3 g −1.[ 21 ] To obtain higher SSE, various preparation methods of CPC-based foams are developed to further decrease the density or improve the SE at similar thickness. Zheng group [ 20 ] reported a facile phase separation method to fabricate lightweight microcellular graphene/polyetherimide (PEI) and graphene@Fe 3 O 4 /PEI composites with density near 0.3 g cm −3 and SSE ≈40 dB cm 3 g −1 at 2.3-2.5 mm thickness. Yan et al. fabricated porous graphene/ PS composites with density of 0.27 and 0.45 g cm −3 by a combination of high-pressure compression molding and salt-leaching method, and the SSE was as large as 64.4 dB cm 3 g −1 in the X-band at 2.5 mm thickness, due to successful preparation of low-density porous composites with the loading of graphene as high as 30 wt%. [ 10 ] However, SE of those porous composites are still not high enough when the densities are relatively low, and SSE of those CPC-based foams are limited at similar thickness.For a certain thickness, improving the conductivities of CPCs is an effective way to improve SE by increasing the loadings of electric fi llers with high conductivity. Nevertheless, the conductive network in the matrix will inevitably be impaired in the foaming process and results in a lower conductivity

Electromagnetic interference shielding properties and mechanisms of chemically reduced graphene aerogels

“…2). The observation was contradictory to the previous outcomes that higher electrical conductivity [1,12,38,44] or better connected network [13,[45][46][47] contributed to higher EMI SE. In our case, the amount of rGO within GA could be increased by increasing either the thickness of the GA or the initial GO concentration.…”

Microstructure Design of Lightweight, Flexible, and High Electromagnetic Shielding Porous Multiwalled Carbon Nanotube/Polymer Composites

“…As regards the porous structure, it has been assumed that the cell‐wall surfaces, namely, the interfaces between the frame and the void, may improve the shielding performance, but yet to be clarified through the design of direct and detailed experiments . Besides, the attempt of pore‐shape optimization has been made in our previous work by introducing anisotropic microcells into the multiwalled carbon nanotube (MWCNT)/polymer composites, but lack of comparison between various pore types. In short, tuning the microstructure of the porous CPCs, in order to effectively utilizing the intrinsic shielding property of the frame materials, is challenging for researchers.…”

“…By effective utilization of the cell walls, EMI SE can reach as high as 46.7 dB in the microwave X‐band with the relevant density of merely 32.3 mg cm −3 , and the lowest density 9.0 mg cm −3 is accomplished with an SE just slightly beyond the commercial shielding requirement (20 dB) . To simultaneously characterize the shielding ability and the lightweight property of a material, instead of using the commonly appeared specific SE (SSE, defined as the SE divided by the density), it is appropriate to use the SSE divided by thickness (SSE/ d for brevity, with d denoting the thickness of sample) . The maximum SSE/ d of our samples is up to 1.04 × 10 4 dB cm 2 g −1 , significantly exceeds the CPCs with other fillers ever reported.…”

Oriented Arrangement: The Origin of Versatility for Porous Graphene Materials

“…The sensitivity of OPG in low‐pressure state is higher than ever reported graphene‐based pressure sensors shown in Figure d . More importantly, the oriented arrangement gifts the OPG sensor a highly sensitive resistance response under a ultralow stress less than 0.5 kPa with a wide strain range from 0 to 70% strain state, which exhibits apparent advantage over other sensors reported in previous works (Figure e) …”