Ultralightweight silver nanowires (AgNWs) hybrid polyimide (PI) composite foams with microcellular structure and low density of 0.014-0.022 g/cm(3) have been fabricated by a facile and effective one-pot liquid foaming process. The tension flow generated during the cell growth induced the uniform dispersion of AgNWs throughout the cell walls. The interconnected AgNWs network in the cell walls combined with the large 3D AgNWs network caused by 3D structure of foams provided fast electron transport channels inside foams. The electromagnetic interference (EMI) shielding effectiveness (SE) of these foams increased with increasing AgNWs loading as well as the nanowire aspect ratio due to the increasing connections of the conduction AgNWs network. Appropriate surface treatment like etching or spraying facilitated the construction of the seamlessly interconnected 2D AgNWs network on the surface, which could effectively reflect electromagnetic waves. Maximum specific EMI SE of values of 1210 dB·g(-1)·cm(3) at 200 MHz, 957 dB·g(-1)·cm(3) at 600 MHz, and 772 dB·g(-1)·cm(3) at 800-1500 MHz were achieved in sprayed composite foams containing <0.044 vol % AgNWs loading, which far surpasses the best values of other composite materials. The reflections of interconnected AgNWs networks on the surface and inside foams combined with the multiple reflections at interfaces contributed to the shielding effect.

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Silver nanofillers of three different shapes were synthesized: silver nanospheres (AgNSs), silver nanowires (AgNWs) and silver nanowires-silver nanoplatelets (AgNWPs). Ultra-lightweight polyimide (PI) composite foams filled with these three silver nanofillers were fabricated by a facile and effective one-pot liquid foaming process, respectively. Their microstructure, electromagnetic interference (EMI) shielding effectiveness (SE) and shielding mechanisms were investigated. It was found that, at the same nanofiller loading, the EMI SE of the composite foams decreased in the following order: AgNWPs > AgNWs > AgNSs. AgNWPs/PI composite foams exhibited the highest EMI SE owing to the denser 3D conductive network of AgNWPs compared to AgNWs and AgNSs, in which the seamlessly interconnected AgNWPs network provided fast electron transport channels inside foams. Maximum specific EMI SE values of 1208 dB g À1 cm 3 at 200 MHz, 650 dB g À1 cm 3 at 600 MHz, and 488 dB g À1 cm 3 in the frequency ranges of 800-1500 MHz, 216-249 dB g À1 cm 3 at 8-12 GHz were achieved in the composite foams at 4.5 wt% AgNWPs loading, which far surpass the best values of other composite materials. The reflections of interconnected AgNWPs networks inside the foams combined with absorptions resulting from the multiple reflections at interfaces inside the foams contributed to the shielding effect. This suggests that our AgNWPs/PI composite foams have excellent potential as high-performance EMI shielding materials against electromagnetic interference pollution in applications that need lightweight. Fig. 7 Dispersion of silver nanostructures in composite foams for PIF-P, PIF-W and PIF-WS: (middle) FESEM images of cell walls; (left) FESEM images of the distribution of silver nanostructures in cell membranes; (right) FESEM images of the distribution of silver nanostructures in cell walls.This journal is

One-dimensional Ag-Fe3O4 core-shell heteronanowires have been synthesized by a facile and effective coprecipitation method, in which silver nanowires (AgNWs) were used as the nucleation site for growth of Fe3O4 in aqueous solution. The size and morphology control of the core-shell nanowires were achieved by simple adjustments of reaction conditions including FeCl3/FeCl2 concentration, poly(vinylpyrrolidone) (PVP) concentration, reaction temperature, and time. It was found that the Fe3O4 shell thickness could be tuned from 6 to 76 nm with the morphology variation between nanopheres and nanorods. A possible growth mechanism of Ag-Fe3O4 core-shell nanowires was proposed. First, the C═O derived from PVP on the surface of AgNWs provided nucleation points and in situ oxidation reaction between AgNWs and FeCl3/FeCl2 solution promoted the accumulation of Fe(3+) and Fe(2+) on the AgNWs surface. Second, Fe3O4 nanoparticles nucleated on the AgNWs surface. Lastly, Fe3O4 nanoparticles grew on the AgNWs surface by using up the reagents. Higher FeCl3/FeCl2 concentration or higher temperature led to faster nucleation and growth, resulting in the formation of Fe3O4 nanorods, whereas lower concentration or lower temperature resulted in slower nucleation and growth, leading to the formation of Fe3O4 nanospheres. Furthermore, the Ag-Fe3O4 core-shell nanowires exhibited good electrical properties and ferromagnetic properties at room temperature. Particularly, the magnetic saturation values (Ms) increased from 5.7 to 26.4 emu g(-1) with increasing Fe3O4 shell thickness from 9 to 76 nm. This growth of magnetic nanoparticles on 1D metal nanowires is meaningful from both fundamental and applied perspectives.