Flexible Fe3O4/graphene foam/poly dimethylsiloxane composite for high-performance electromagnetic interference shielding
Introduction
In order to reduce the harmful effects of electromagnetic wave on electronic equipment and human's health and satisfy the demands for aerospace and flexible electronics, etc., it is becoming more and more urgent to exploit electromagnetic interference (EMI) shielding materials of light weight, flexibility, corrosion resistance and high performance [[1], [2], [3]]. Recently, conductive polymer composites made up of polymers and conducting fillers have been served as a kind of modern EMI shielding materials [2,[4], [5], [6]]. Generally, the polymers are insulating and nonmagnetic, but can endow the composite with the properties of lightness, elasticity, excellent process-ability and mechanical features etc. [7,8] And the conductive fillers of incorporating into the polymer matrices play the key role in attenuating incident electromagnetic wave by the constructed conductive networks. Among the conductive fillers, the 2D graphene has drawn more attentions due to the characteristics of high electrical conductivity, low density, corrosion resistance, high temperature resistance, easy processing and excellent EMI shielding effectiveness (SE) etc. [1,[9], [10], [11], [12]] Therefore, many graphene-based conductive polymer composites have been fabricated by filling graphene into polymers and obtained high-performance EMI shielding [[13], [14], [15], [16], [17]]. In more recent years, the synergistic effect between graphene and CNTs has been the focus of attention in graphene-based conductive polymer composites. The weak electronic coupling between graphene sheets can be significantly improved by the formed filling and bridging effects via the embedding of CNTs, thus the lightweight and flexible CNTs/graphene/polymers composites with enhanced EMI shielding performance have been designed and fabricated [[18], [19], [20], [21]]. In a typical instance, Zhu et al. reported that the EMI SE of the flexible oxidized MWCNTs (OCNTs)/graphene/poly dimethylsiloxane (PDMS) composites reached 57.3 dB which exceeded the summation of that of the separate OCNTs/PDMS (2.5 dB) and graphene/PDMS (50.3 dB) [17].
Additionally, it is well known that the magnetic property plays an important role in attenuating the incident EMI wave. As the ferromagnetic materials have the advantages of high magnetism, eco-friendliness, low cost, rich mineral reserves and so on, the conductive fillers that electronic conductive graphene loading magnetic ferromagnetic materials such as γ-Fe2O3 [22], Fe3O4 [[23], [24], [25], [26], [27], [28], [29], [30]], carbonyl iron [31,32], etc. have been many researches in electromagnetic shielding. The Fe3O4 exhibits excellent magnetic property, which can lead to magnetic attenuation [33] and produce much better EMI shielding performance [23,24]. Zhan et al. [23] fabricated flexible Fe3O4/rGO/natural rubber (NR) nanocomposites. While the rGO content was 10 wt% of NR, the EMI SE of Fe3O4/rGO/NR reached 26.4 dB mm−1 in the frequency range of 8.2–12.4 GHz, which was 1.4 times of that of rGO/NR nanocomposite at the same rGO content. Although the EMI shielding performance was improved by introducing Fe3O4 attenuating the incident electromagnetic wave, what should not be overlooked is that the additional Fe3O4 was more than 3.5 times amount comparing with that of rGO in rGO/NR or Fe3O4/rGO/NR nanocomposites. What is worse, the anchored Fe3O4 nanoparticles have adverse effect on the mutual electronic contact of rGO sheets in Fe3O4/rGO/polymer composite. For instance, Shen et al. [24] fabricated polyetherimide (PEI)/graphene@Fe3O4 composite foam, the electrical conductivity of which was lower than that of the PEI/graphene composite at the same filler content. The relative drop electrical conductivity should be due to the prevented mutual direct electrical contact of the graphene sheets by the anchored Fe3O4 nanoparticles [3]. Although the declined conductivity decreased the SE of reflection (SER), the SE of absorption (SEA) was enhanced by increased dielectric loss and magnetic loss [24]. Similarly, the synergistic effect between electronic conductive graphene and magnetic Fe3O4 has been confirmed by amounts of reports in microwave absorption [[34], [35], [36], [37], [38], [39], [40], [41]].
As is well known, the direct physical contact between the conductive fillers can form conductive network [10,42] and the highly conductive network plays a prominent role in attenuation of electromagnetic radiation [8]. However, simply increasing filler content to form conductive network could lead to difficult processing technology and poor mechanical properties [3]. More interestingly, the seamlessly interconnected 3D conductive network can be constructed by a catalyst chemical vapour deposition (CVD) method [1,43,44]. And the GF would own the good flexibility by coating a thin layer of PDMS [1,43,44]. Chen et al. [1] prepared a flexible, lightweight and interconnected 3D GF/PDMS composite with a low density of 0.06 g cm−3. And the EMI SE is as high as 20 dB in the X-band, which has no obvious degradation even after bending 10000 times. In addition, Kong et al. fabricated a carbon nanowires (CNWs)/GF/PDMS composite with a low density of 97.1 mg cm−3. And the composite exhibited a high EMI SE of 36 dB in the X-band [43].
In this work, the GF was fabricated by a CVD method and the hexadecyl trimethyl ammonium bromide (CTAB) - decorated magnetic Fe3O4 nanoparticles are assembled onto electronic conductive GF on the role of mutual electrostatic attraction in aqueous medium. The anchored Fe3O4 nanoparticles have any weakening or strengthening effect on the contact resistance of the fixed shaped graphene in the 3D structural Fe3O4/GF composite. Therefore, the EMI SE of the composite can directly make clear the synergistic effect between electronic conductive graphene and magnetic Fe3O4. Ultimately, the lightweight Fe3O4/GF/PDMS composite reaches a high EMI SE of about 32.4 dB in the frequency range of 8.2–12.4 GHz. By contrast, the EMI SE of single GF/PDMS and Fe3O4/PDMS/polytetrafluoroethylene (PTFE) composite reaches 26.7 and 0.15 dB, respectively. Obviously, the results confirmed the synergistic effect between graphene and Fe3O4. Furthermore, the flexible Fe3O4/GF/PDMS composite still keeps an EMI SE of about 31.5 dB after repeatedly bending for 500 cycles.
Section snippets
Fabrication of GF
Firstly, nickel foams (110 ppi, 500 g m−2 in area density, about 1.6 mm in thickness, HGP technology CO., LTD, China) were successively washed by acetone, ethanol and deionized water. Four pieces of dried nickel foams with a diameter of about 20 × 30 mm2 were heated to 950 °C under Ar (30 sccm (standard cubic centimeter per minute)) and H2 (30 sccm) at a heating rate of 20 °C min−1 using a horizontal tube furnace (TF55030C, Lindberg Blue M, USA) equipped a quartz tube with an inside diameter of
Results and discussion
The preparation process of Fe3O4/GF/PDMS composite is schematically depicted in Fig. 1. The GF is grown on the surface of Ni foam by a CVD method, similar to the previous reports [1,43,44]. And the 3D structural GF is obtained after etching the Ni by 3 M HCl at 80 °C for 24 h. The Fe3O4 nanoparticles are synthesized by a hydrothermal method using Fe(OH)3 sol as precursor [45]. After modified by CTAB, the Fe3O4 nanoparticles show positive charge [46,47]. Fig. 1b shows the respective zeta
Conclusion
In this work, the Fe3O4/GF/PDMS composite of high EMI SE and excellent mechanical properties was successfully fabricated. The density of the composite is just only 0.13 g cm−3, and the EMI SE is as high as 32.4 dB in the frequency of 8.2–12.4 GHz. Even after 10000 cycles of repeated bending, the EMI SE of the composite remains 29.4 dB. The reflection shielding is not weakened because the loaded Fe3O4 nanoparticles have no influence on the electronic contact of highly conductive graphene sheets,
CRediT authorship contribution statement
Shoupu Zhu: Data curation, Formal analysis, Writing - original draft. Qing Cheng: Data curation, Formal analysis. Congcong Yu: Data curation, Formal analysis. Xiaochun Pan: Writing - review & editing. Xiaobo Zuo: Writing - review & editing. Jianfei Liu: Writing - review & editing. Mingliang Chen: Writing - review & editing. Weiwei Li: Writing - review & editing. Qi Li: Supervision, Writing - review & editing. Liwei Liu: Supervision.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work was supported by the National Natural Science Foundation of China [Grant Nos. 61605237 and 51972330], the Military Commission Logistics Department [Grant Nos. BY117J013], the State Key Program of National Natural Science Foundation of China [Grant No. 61734008], Jiangsu Province Postdoctoral Research Funding Scheme [Grant No. 2018K158C], Youth Support Project of Key Laboratory of Nano Devices and Applications of Chinese Academy of Sciences [Grant No. Y4JA21001]. We also thank the
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