Galvanic Replacement Reaction Involving Core–Shell Magnetic Chains and Orientation‐Tunable Microwave Absorption Properties

Abstract

Electromagnetic (EM) wave absorption materials have attracted considerable attention because of EM wave pollution caused by the proliferation of electronic communication devices. One‐dimentional (1D) structural magnetic metals have potential as EM absorption materials. However, fabricating 1D core–shell bimetallic magnetic species is a significant challenge. Herein, 1D core–shell bimetallic magnetic chains are successfully prepared through a modified galvanic replacement reaction under an external magnetic field, which could facilitate the preparation of 1D core–shell noble magnetic chains. By delicately designing the orientation of bimetallic magnetic chains in polyvinylidene fluoride, the composites reveal the decreased complex permittivity and increased permeability compared with random counterparts. Thus, elevated EM wave absorption perfromances including an optimal reflection loss of −43.5 dB and an effective bandwidth of 7.3 GHz could be achieved for the oriented Cu@Co sample. Off‐axis electron holograms indicate that the augmented magnetic coupling and remarkable polarization loss primarily contribute to EM absorption in addition to the antenna effect of the 1D structure to scatter microwaves and ohmic loss of the metallic attribute. This work can serve a guide to construct 1D core–shell bimetallic magnetic nanostructures and design magnetic configuration in polymer to tune EM parameters and strengthen EM absorption properties.

Non-Magnetic Bimetallic MOF-Derived Porous Carbon-Wrapped TiO2/ZrTiO4 Composites for Efficient Electromagnetic Wave Absorption

“…The EMW absorption performances were evaluated by RL values, and calculated based on the transmission line theory in the metal backboard model by Eqs. ( 1 ) and ( 2 ) [ 13 , 34 , 35 ]: in which Z in and Z 0 represented the input impedance and free space impedance; ε r and μ r referred to the relative complex permittivity and permeability; c and were the vacuous light velocity and absorber thickness, respectively. The three-dimensional RL representations (Fig.…”

“…Making use of the enhanced interface polarization, the effective absorption bandwidth (EAB) was broadened evidently (4.9 GHz, 3.0 mm). As these examples indicated, most researchers focused on the investigation of magnetic MOF derivatives because high permeability arising from magnetic components would optimize the impedance matching characteristics, which is beneficial to strengthen the absorption intensity and reduce the matching thickness [ 10 – 13 ]. However, the magnetic nanoparticles such as Fe, Co, Ni, and their alloys are suffering from high material density and low chemical stability [ 14 ], which limited their further practical application.…”

Lightweight Ni Foam‐Based Ultra‐Broadband Electromagnetic Wave Absorber

“…Though efforts have been devoted to design efficient EM wave absorbers by elaborate micro/nano-structure design or reaching impedance matching by compositing metal oxides with low conductivity on metals' surface to solve above problems, [6][7][8][9][10][11] there are still many challenges awaiting. For instance, for the former route, [6][7][8][9] micro/nano-structure metals such as metal nanochains have been fabricated as an alternative to solve high density issue of bulk metals. However, their high surface energy will lead to agglomeration and is adverse to well dispersibility, [12][13][14] thus deteriorating EM wave absorption performance.…”

Fabrication of Cellulose Nanofiber/Reduced Graphene Oxide/Nitrile Rubber Flexible Films Using Pickering Emulsion Technology for Electromagnetic Interference Shielding and Piezoresistive Sensor

“…The segregated structure of NBR can significantly increase the interface area between the RGO and the NBR, which leads to more interfacial polarization loss and dielectric loss to generate the attenuation of incident EM waves. [43][44][45][46] As the GO mass fraction increased, the increased conductivity of the films still maintained the same order of mag-nitude, which resulted in the most limited ability of reflecting EM waves. In contrast, an excessive amount of RGO wrapping NBR microspheres in the final composite films can possibly lead to the multilayered structure of RGO and increase the interfacial between the RGO and the NBR.…”

“…The EM wave energy can be attenuated by the intensive interfacial polarization loss and dielectric loss. [43,46] Moreover, the unique 3D conductive network of RGO can still afford conductive loss by converting EM wave energy into heat. Therefore, for the CNF-RGO/NBR composite films, the incident EM waves were first almost completely reflected, owing to their excellent electrical conductivity, whereas the EM waves entering the interior of the films were attenuated mainly by the interfacial polarization loss, dielectric loss, and conductive loss.…”