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

The exceptional thermal conductivity of graphene is expected to endow polymer composites with ultrahigh thermal conductivities, which can be even similar to those of some metals such as stainless steel and aluminum alloy. The thermal conductivities of composites prepared by dispersing multilayer graphene (MLG) in epoxy matrix increase only by an order of magnitude over the pure epoxy. However, the improvement has been limited since the large interfacial thermal resistance exists between graphene and the surrounding epoxy. We have reported an extraordinary increase in thermal conductivity of the MLG/epoxy composites through the fabrication of the vertically aligned and densely packed MLG in the epoxy matrix. The ultrahigh thermal conductivity of 33.54 W/(m K) has been achieved in the aligned MLG/epoxy composite (AG/E). The thermal conductivity of AG/E exhibits a positive temperature response related to the aligned structure while increasing the temperature from 40 °C to 90 °C.

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Multiwalled carbon nanotube/polymer composites with aligned and isotropic micropores are constructed by a facile ice-templated freeze-drying method in a wide density range, with controllable types and contents of the nanoscale building blocks, in order to tune the shielding performance together with the considerable mechanical and electrical properties. Under the mutual promotion of the frame and porous structure, the lightweight high-performance shielding is achieved: a 2.3 mm thick sample can reach 46.7 and 21.7 dB in the microwave X-band while the density is merely 32.3 and 9.0 mg cm , respectively. The lowest density corresponds to a value of shielding effectiveness divided by both the density and thickness up to 10 dB cm g , far beyond the conductive polymer composites with other fillers ever reported. The shielding mechanism of the flexible porous materials is further demonstrated by an in situ compression experiment.