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Nanocomposite foam with a large expansion ratio and thin cell walls is promising for electromagnetic interference (EMI) shielding materials, due to the low electromagnetic (EM) reflection and high EM absorption. To overcome the dimensional limitation from two-dimension (2D) thin walls on the construction of conductive network, a strategy combining hybrid conductive nanofillers in semi-crystalline matrix together with supercritical CO2 (scCO2) foaming was applied: (1) one-dimension (1D) CNTs with moderate aspect ratio was used to minimize the dimensional confinement from 2D thin walls while constructing the main EM absorbing network; (2) zero-dimension (0D) carbon black (CB) with no dimensional confinement was used to connect the separated CNTs in thin walls and to expand the EM absorbing network; (3) scCO2 foaming was applied to obtain a cellular structure with multi-layer thin walls and a large amount of air cells to reduce the reflected EM; (4) semi-crystalline polymer was selected so that the rheological behavior could be adjusted by optimizing crystallization and filler content to regulate the cellular structure. Consequently, an advanced material featured as lightweight, high EM absorption and low EM reflection was obtained at 0.48 vol.% hybrid nanofillers and a density of 0.067 g/cm3, whose specific EMI shielding performance was 183 dB cm3/g.

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For carbon nanofiber/poly(vinylidene fluoride) (CNF/PVDF) nanocomposite materials, the strong interactions between nanofillers would induce agglomeration and hence significantly deteriorate both the electromagnetic interference (EMI) shielding and thermal conductivity of materials. In this work, an effective supercritical fluid-assisted thin cell wall stretching−defoaming method was proposed to improve the nanofiller dispersion of CNF/PVDF nanocomposites. Meanwhile, the relationship between the nanofiber 3D network structure and the cell growth of foaming was studied in depth via a biaxial stretching experiment and a Monte Carlo simulation. By using this method, the nanocomposite performance was enhanced: (1) at a low filler content, the 3D stretching is beneficial for improving the nanoscale interface in nanocomposites, that is, increasing the dielectric permittivity (increased by 183.7%), decreasing the dielectric loss, and increasing the breakdown strength (increased by 87.1%), and (2) at a high filler content, the 3D stretching is beneficial for improving the macroscale network. That is, the EMI increased by 46.4% and the thermal conductivity increased by 27.3%.