epoxy electromagnetic interference shielding nanocomposites

epoxy electromagnetic interference shielding nanocomposites

Composites Science and Technology 169 (2019) 70–75 Contents lists available at ScienceDirect Composites Science and Technology journal homepage: www...

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Composites Science and Technology 169 (2019) 70–75

Contents lists available at ScienceDirect

Composites Science and Technology journal homepage: www.elsevier.com/locate/compscitech

Fabrication and investigation on the Fe3O4/thermally annealed graphene aerogel/epoxy electromagnetic interference shielding nanocomposites

T

Yiming Huangfua,1, Chaobo Lianga,1, Yixuan Hana, Hua Qiua, Ping Songa, Lei Wanga, Jie Konga,∗∗, Junwei Gua,b,∗ a MOE Key Laboratory of Material Physics and Chemistry Under Extraordinary Conditions, Shaanxi Key Laboratory of Macromolecular Science and Technology, Department of Applied Chemistry, School of Science, Northwestern Polytechnical University, Xi'an, Shaanxi, 710072, PR China b Institute of Intelligence Material and Structure, Unmanned System Research Institute, Northwestern Polytechnical University, Xi'an, Shaanxi, 710072, PR China

A R T I C LE I N FO

A B S T R A C T

Keywords: A. Nanocomposites A. Graphene B. Electrical properties B. Magnetic properties E. Casting

Ethylenediamine functionalized Fe3O4 (NH2-Fe3O4) nanoparticles and graphene oxide (GO) were compounded firstly, followed by the addition of L-ascorbic acid, to obtain the Fe3O4/thermally annealed graphene aerogel (Fe3O4/TAGA) by thermal annealing method. And the Fe3O4/TAGA/epoxy nanocomposites were then fabricated via template-casting method. When the mass ratio of GO to NH2-Fe3O4 was 2:1 and the total mass fraction of Fe3O4/TAGA was 2.7 wt% (1.5/1.2 wt% Fe3O4/TAGA), the obtained Fe3O4/TAGA/epoxy nanocomposites presented the highest electromagnetic interference shielding effectiveness (EMI SE of 35 dB in the X-band), much higher than that of epoxy nanocomposites (10 dB) filled with the same Fe3O4/thermal annealing graphene oxide (Fe3O4/TAGO) loading. Meantime, the corresponding Fe3O4/TAGA/epoxy nanocomposites also presented the outstanding electrical conductivity of 27.5 S/m.

1. Introduction Increasingly widespread penetration of the electronic products brings us increasing electromagnetic pollution, which not only endangers human health, but also affects the normal use of other electronic devices [1–3]. In this context, electromagnetic interference (EMI) materials have attracted extensive attention [4–7]. Conductive carbon/polymer composites possess light weight, corrosion resistance and excellent EMI properties, etc. [8–13]. Graphene also presents the potential to become an alternative material for EMI, due to its high specific surface area and excellent electrical conductivity [14–18]. However, the relatively poor dispersion of graphene inner polymer matrix has restricted its broader application in the high-performance & multifunctional polymer composites [19–22]. Constructing three-dimensional graphene structure by self-assembling method [23], finally to form the graphene aerogel or foam, can effectively avoid the agglomeration of graphene. Moreover, the conductive networks can be effectively formed with the pretty low graphene loading [24–27]. Wan et al. [28] reported that the introduction of 3D graphene aerogel (GA) could significantly enhance the EMI of the GA/epoxy composites. Li

et al. [29] prepared the thermally annealed GA (TAGA)/epoxy nanocomposites, and the EMI shielding effectiveness (EMI SE) value of the epoxy composites with 0.2 wt% TAGA could reach 25 dB in the X-band. Additionally, the EMI SE value of the graphene/polydimethylsiloxane foams by chemical vapor deposition (CVD) was also beyond 30 dB reported by Chen and corworkers [30]. To our knowledge, polymer composites with single graphene are difficult to achieve relatively high EMI SE value. Combining graphene with magnetic materials (such as iron, cobalt, nickel and their oxides, etc.) can be in favour of enhancing the EMI SE values of the polymer composites [31–33]. Ferroferric oxide (Fe3O4) nanoparticles present to be one of the commonest EMI materials, owing to their low toxicity, good biocompatibility and high saturation magnetization [34–37]. Chen [38] and the corworkers introduced Fe3O4 nanoparticles into the thermally annealing graphene oxide (TAGO)/polystyrene composites to obtain the EMI SE value of 30 dB, higher than that of TAGO/polystyrene composites (25 dB) with the same TAGO loading. Shen [39] et al. fabricated reduced GO (RGO)@Fe3O4/polyetherimide composites, and the addition of Fe3O4 nanoparticles could greatly improve the EMI SE value. However, there are still few reports about the fabrication of

∗ Corresponding author. MOE Key Laboratory of Material Physics and Chemistry Under Extraordinary Conditions, Shaanxi Key Laboratory of Macromolecular Science and Technology, Department of Applied Chemistry, School of Science, Northwestern Polytechnical University, Xi'an, Shaanxi, 710072, PR China. ∗∗ Corresponding author. E-mail addresses: [email protected] (J. Kong), [email protected], [email protected] (J. Gu). 1 The authors Yiming Huangfu and Chaobo Liang contributed equally to this work and should be considered co-first authors.

https://doi.org/10.1016/j.compscitech.2018.11.012 Received 30 August 2018; Received in revised form 1 November 2018; Accepted 5 November 2018 Available online 09 November 2018 0266-3538/ © 2018 Elsevier Ltd. All rights reserved.

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samples were investigated using a vibrating sample magnetometer (VSM) at room temperature. Direct current (DC) electrical conductivity of the samples was measured by a four-probe method, and the dimension of the samples was 22.86 mm × 10.16 mm × 3.00 mm. EMI shielding parameters of the samples were tested by VNA (MS4644A, Anritsu) using the wave-guide method in the X-band frequency (8.2–12.4 GHz) range according to ASTM D5568-08, and the dimension of the samples was 22.86 mm × 10.16 mm × 3.00 mm.

EMI polymer composites from composite aerogels of Fe3O4/GO. Epoxy resins possess excellent comprehensive properties and present broad industrial applications in the fields of electronics, aerospace and marine systems, etc [40–44]. In our present work, graphene oxide (GO) was firstly prepared by modified Hummers method [45], which was then compounded with ethylenediamine (EN) functionalized Fe3O4 nanoparticles (NH2-Fe3O4) [46]. And the Fe3O4/thermally annealed graphene aerogel (Fe3O4/TAGA) was then obtained with the addition of L-ascorbic acid [47] by thermal annealing method. Finally, the Fe3O4/ TAGA/epoxy nanocomposites were fabricated via template-casting method. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), scanning electron microscope (SEM) and vibrating sample magnetometer (VSM) were performed to analyze and characterize the structures and performance of the Fe3O4, NH2-Fe3O4, Fe3O4/GO, Fe3O4/GA, Fe3O4/TAGA and Fe3O4/TAGA/epoxy nanocomposites. Furthermore, the mass ratio of GO to NH2-Fe3O4 and the total mass fraction of Fe3O4/ TAGA on the electrical conductivities and EMI SE values of the Fe3O4/ TAGA/epoxy nanocomposites were discussed and investigated.

3. Results and discussion Fig. 2 shows the FTIR (a) and XPS (b) spectra of the Fe3O4 and NH2Fe3O4 nanoparticles. Compared to that of pristine Fe3O4, NH2-Fe3O4 (a) present two new characteristic peaks, ascribed to the bending vibration of N-H (1550 cm−1) and the stretching vibration of C-N (1317 cm−1). Characteristic peaks in XPS spectra at 711.0 eV, 724.0 eV and 54.0 eV is corresponded to Fe 2p3/2, Fe 2p1/2 and Fe 3p, respectively. NH2-Fe3O4 presents a new characteristic absorption peak of nitrogen around 400 eV, indicating that Fe3O4 nanoparticles have been successfully ammoniated. Fig. 3 presents the FTIR (a) and XPS (b) spectra of the GA, Fe3O4/GA and Fe3O4/TAGA. Peaks of GA at 3385 cm−1, 1745 cm−1, 1254 cm−1 and 1034 cm−1 is assigned to the characteristic absorption of O-H, C] O, C-O-C and C-OH group, respectively [48]. New appearance of peak for Fe3O4/GA at 583 cm−1 is ascribed to Fe-O group, and the peaks of C-OH and C-O-C groups are also disappeared. For Fe3O4/TAGA, the weakened peak of O-H group and disappeared peak of C]O group can prove that thermal annealing treatment has removed most of the oxygen-containing groups of GO [49]. For XPS spectra of Fe3O4/GA and Fe3O4/TAGA, the new characteristic twin peaks of Fe 2P3/2 (711.0 eV) and Fe 2P1/2 (724.0 eV) are both appeared. And the oxygen content is further decreased for Fe3O4/TAGA. In addition, from C 1s of GA, there are four characteristic peaks at 284.6 eV (C-C), 285.6 eV (C-O), 287.0 eV (C]O), and 288.6 eV (O-C]O). Fe3O4/GA (C 1s) presents a new characteristic peak at 285.5 eV (C-N), resulted from the reaction between NH2-Fe3O4 and carboxyl/epoxy groups on the surface of GO. Two characteristic peaks of O-C]O and C-N for Fe3O4/TAGA are both disappeared, and two peaks of C-O and C]O are also weakened. Magnetic properties of Fe3O4, NH2-Fe3O4, Fe3O4/GA and Fe3O4/ TAGA at room temperature are shown in Fig. 4. Compared with that of Fe3O4, the saturation magnetization of NH2-Fe3O4 is reduced from 62.1 emu/g to 58.3 emu/g, mainly ascribed to the grafting amino groups on the surface of Fe3O4. Meantime, GA also presents a certain saturation magnetization (7.8 emu/g) with the addition of NH2-Fe3O4. After the thermal annealing treatment, the saturation magnetization of Fe3O4/ TAGA is increased to 13.9 emu/g. The reason is that the non-magnetic functional groups on the surface of NH2-Fe3O4 and the corresponding oxygen-containing functional groups of GA are also decreased till removed. NH2-Fe3O4 nanoparticles are successfully attached to GO's surface (Fig. 5(a)). Fe3O4/TAGA presents an obvious pore structure (b), beneficial to the absorption and reflection of electromagnetic waves, in favour of improving the EMI SE value. In addition, the epoxy resins are uniformly dispersed inner the pores of Fe3O4/TAGA (1.5/1.2 wt%, c), presenting smooth and dense, which reveals that the epoxy resins possess good interfacial compatibility with Fe3O4/TAGA [39,50]. Electrical conductivities of the TAGA/epoxy (a), Fe3O4/TAGA/ epoxy (b) and Fe3O4/TAGO/epoxy (c) nanocomposites are shown in Fig. 6. The electrical conductivities of the TAGA/epoxy nanocomposites are increased from 23.5 S/m (0.3 wt% TAGA) to 30.3 S/m (1.2 wt% TAGA) with the increase of TAGA loading, mainly ascribed to more conductive networks of TAGA. With the further addition of NH2-Fe3O4, the electrical conductivities of the Fe3O4/TAGA/epoxy nanocomposites are slightly decreased to 27.5 S/m (1.5/1.2 wt% Fe3O4/TAGA), but still remains at a relatively high level [51]. The reason is that the introduction of NH2-Fe3O4 nanoparticles can increase the interfacial

2. Experimental 2.1. Main materials Graphite flake (325 mesh) was provided by Alfa Aesar Co. Ltd. (Shanghai, China). Ethylenediamine (EN, C2H8N2, ≥99%) was purchased from Beijing Chemical Factory (Beijing, China). L-ascorbic acid (C6H8O6, ≥99.99%) was supplied by Macklin (Xi'an, China). Ferroferric oxide (Fe3O4) nanoparticles were obtained from Nanjing Emperor Nano Material Co., Ltd. (Jiangsu, China). Bisphenol F epoxy (Epon 862) and the corresponding curing agent of 2, 4-diethyl-6-methylbenzene-1, 3-diamine (EK 3402) were both provided by Hexion Inc (Columbus, USA). 2.2. Fabrication of epoxy nanocomposites i. GO was firstly prepared by modified Hummers method [45], followed by thermally annealed at 800 °C for 30 min under N2 atmosphere to obtain TAGO. Fe3O4 was also functionalized by EN (NH2Fe3O4) according to previous work [46]. Then the hybrid fillers of Fe3O4/TAGO were added into the Epon 862/EK 3402 (100/26.5, wt/wt) mixtures, followed by mechanically stirred at 70 °C for 1 h, then heated to 120 °C for 5 h, finally to obtain the Fe3O4/TAGO/ epoxy nanocomposites. ii. GO was firstly ultrasonically dispersed in deionized water for 20 min. NH2-Fe3O4 (NH2-Fe3O4/GO, 1/8, 1/4 and 1/2, wt/wt) was then added into the above solution and stirred at 60 °C for 2 h. After cooled to room temperature, L-ascorbic acid (L-ascorbic acid/GO, 2/ 1, wt/wt) was then added and kept ultrasonic treatment for 10 min, followed by heated to 40 °C for another 12 h, finally to obtain the Fe3O4/GO hydrogel. Then Fe3O4/GO hydrogel was frozen in liquid nitrogen and freeze-dried at −56 °C for 48 h, followed by thermally annealed at 800 °C for another 30 min under N2 atmosphere to obtain the Fe3O4/TAGA aerogel. Epon 862 and EK 3402 were stirred at 70 °C for 1 h, and then immersed by Fe3O4/TAGA aerogel, then heated to 120 °C for 5 h, finally to obtain the Fe3O4/TAGA/epoxy nanocomposites (shown in Fig. 1). 2.3. Characterizations FTIR of the samples were obtained on a Bruker Tensor 27 equipment (Bruker Corp., Germany). XPS analyses of the samples were carried out using PHI5400 equipment (PE Corp., England). Morphologies of the samples were obtained by SEM (VEGA3-LMH, ESCAN Corporation, Czech Republic). TEM images of the samples were collected on a Talos F200X/TEM microscope (FEI Company). The magnetic properties of the 71

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Fig. 1. Schematic diagram of the fabrication for the Fe3O4/TAGA/epoxy nanocomposites.

Fig. 2. FTIR (a) and XPS (b) spectra of the Fe3O4 and NH2-Fe3O4 nanoparticles.

resistance of Fe3O4/TAGA. Compared with that of Fe3O4/TAGA/epoxy composites, the Fe3O4/TAGO/epoxy composites present relatively ultralow electrical conductivities at the same fillers loading (c). The reason is that small number of Fe3O4/TAGO disperse randomly inner epoxy matrix, hardly to connect each other, presenting small contribution to electrical conductivities. In addition, the intrinsic electrical conductivity of TAGO is also far below than that of TAGA. Total SE (SET) includes reflection SE (SER), absorption SE (SEA) and multiple reflection SE (SEM) [18,22,30], given by Equation (1).

SE T (dB) = SEA + SER + SEM

(1)

(2)

EMI SE is represented by a scattering coefficient, where S11 is a forward reflection coefficient, S12 represents a forward transmission coefficient, S21 is a reverse transmission coefficient, and S12 represents a reverse reflection coefficient. SET, SER and SEA can be calculated by the following Equations:

1 1 SE T (dB) = 10 log10 ⎛⎜ 2 ⎞⎟ = 10 log10 ⎛⎜ 2 ⎞⎟ ⎝ s12 ⎠ ⎝ s21 ⎠

(4)

1 − s2 SEA (dB) = 10 log10 ⎛⎜ 2 11 ⎞⎟ ⎝ s12 ⎠

(5)

Fig. 7(a) shows the EMI SE values of the TAGA/epoxy nanocomposites in the X-band. The EMI SE value of the TAGA/epoxy nanocomposites is increased from 19 dB (0.3 wt% TAGA) to 28 dB (1.2 wt % TAGA) with the increase of TAGA loading. The addition of NH2Fe3O4 can further increase the EMI SE value (35dB, 1.5/1.2 wt% Fe3O4/ TAGA), much higher than that of epoxy nanocomposite (10 dB) filled with the same Fe3O4/TAGO loading (Fig. 7(b)). The reason is that the formed structure of Fe3O4/TAGA can build good conductive networks inner epoxy matrix, beneficial to the improvement of EMI SE value. Meantime, the addition of NH2-Fe3O4 can also produce hysteresis loss of electromagnetic waves, which can further improve the EMI SE value. From Fig. 7(c, c'), with the increase of NH2-Fe3O4 loading, the SEA value of the Fe3O4/TAGA/epoxy nanocomposites is increased from 24 dB to 31 dB, and the SER still maintains at about 4 dB, which can further indicates that the introduction of NH2-Fe3O4 is beneficial to the improvement of EMI SE values.

When SET > 10 dB, SEM can be ignored, then:

SE T (dB) = SEA + SER

1 ⎞ SER (dB) = 10 log10 ⎛⎜ ⎟ 2 − 1 s11 ⎝ ⎠

(3) 72

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Fig. 3. FTIR (a) and XPS (b) spectra of the GA, Fe3O4/GA and Fe3O4/TAGA.

4. Conclusions Thermal annealing treatment could remove most of the oxygencontaining groups of GO, and the obtained Fe3O4/TAGA presented an obvious pore structure, beneficial to the absorption and reflection of electromagnetic waves. Epoxy resins dispersed in the pores of Fe3O4/ TAGA, and presented smooth and dense appearance. When the mass ratio of GO to NH2-Fe3O4 was 2:1 and the total mass fraction of Fe3O4/ TAGA was 2.7 wt% (1.5/1.2 wt% Fe3O4/TAGA), the obtained Fe3O4/ TAGA/epoxy nanocomposites presented the highest EMI SE value of 35 dB in the X-band, much higher than that of epoxy nanocomposite (10 dB) filled with the same Fe3O4/TAGO loading. Meantime, the obtained Fe3O4/TAGA/epoxy nanocomposites also presented outstanding electrical conductivity of 27.5 S/m.

Acknowledgements This work is supported by Space Supporting Fund from China Aerospace Science and Industry Corporation (No. 2018-HT-XG); Foundation of Aeronautics Science Fund (No. 2017ZF53071); Natural Science Basic Research Plan in Shaanxi Province of China (No.

Fig. 4. Magnetization curves of the Fe3O4, NH2-Fe3O4, Fe3O4/GA and Fe3O4/ TAGA.

Fig. 5. TEM image of the Fe3O4/GO (a), and SEM images of the Fe3O4/TAGA (b) and (1.5/1.2 wt%) Fe3O4/TAGA/epoxy nanocomposites (c). 73

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Fig. 6. Electrical conductivities of the TAGA/epoxy (a), Fe3O4/TAGA/epoxy (b) and Fe3O4/TAGO/epoxy (c) nanocomposites.

Fig. 7. EMI SE values of the TAGA/epoxy nanocomposites (a), Fe3O4/TAGO/epoxy nanocomposites (b), and Fe3O4/TAGA/epoxy nanocomposites (c). 74

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