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Accepted Manuscript Effect of electrophoretic condition on the electromagnetic interference shielding performance of reduced graphene oxide-carbon fib...

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Accepted Manuscript Effect of electrophoretic condition on the electromagnetic interference shielding performance of reduced graphene oxide-carbon fiber/epoxy resin composites Jiaming Wu, Juan Chen, Yueying Zhao, Wenxiu Liu, Wenbo Zhang PII:

S1359-8368(16)30095-6

DOI:

10.1016/j.compositesb.2016.08.042

Reference:

JCOMB 4490

To appear in:

Composites Part B

Received Date: 23 March 2016 Revised Date:

29 August 2016

Accepted Date: 30 August 2016

Please cite this article as: Wu J, Chen J, Zhao Y, Liu W, Zhang W, Effect of electrophoretic condition on the electromagnetic interference shielding performance of reduced graphene oxide-carbon fiber/epoxy resin composites, Composites Part B (2016), doi: 10.1016/j.compositesb.2016.08.042. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Effect of electrophoretic condition on the electromagnetic interference shielding performance of reduced graphene oxide-carbon fiber/epoxy resin composites Jiaming WU a,b, Juan CHEN a,b,*, Yueying ZHAO c, Wenxiu LIU a,b, Wenbo ZHANG a,b

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a Shandong Provincial Key Laboratory of Preparation and Measurement of Building Materials, University of Jinan, Jinan 250022, PR China

b School of Material Science and Engineering, University of Jinan, Jinan 250022, PR China

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c Shandong Xiaguang Industrial Co., LTD, Jining 272000, PR China

Abstract

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*Corresponding author: E-mail: [email protected]

Reduced graphene oxide modified carbon fiber (rGO-CF) was synthesized by deposition

and

chemical

reduction.

The

GO

concentration,

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electrophoretic

electrophoretic time and voltage were taken as variables. Epoxy based composites

EP

(rGO-CF/EP) were prepared through molding process and the effects of electrophoretic condition on electromagnetic interference (EMI) shielding performance of rGO-CF/EP

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were studied. Scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy showed that rGO nanosheets were successfully immobilized on CF. The shielding effectiveness (SE) of composites was tested, and the electrophoretic time and voltage have positive impact on SE value. When the voltage increased to 21 V for 60 min, the rGO-CF/EP composite obtained maximum EMI SE of 37.6 dB, which had a 47.6% improvement than that of CF/EP. Furthermore, a high calculated

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ACCEPTED MANUSCRIPT electrical conductivity of 7.20 S/m was achieved at the same condition. Therefore, controlling the electrophoretic condition is available to achieve lightweight high EMI shielding rGO-CF/EP.

deposition;

Polymer-matrix

composites

(PMCs);

Electromagnetic interference

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EP

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shielding.

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Key words: Reduced graphene oxide modified carbon fiber (rGO-CF); Electrophoretic

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ACCEPTED MANUSCRIPT 1. Introduction With the growth of electronics and telecommunications, electromagnetic interference (EMI) shield materials have become the research hotspot for their protection of

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environment, human beings and sensitive circuits [1-4]. The EMI shielding can be achieved by minimizing the signal passing through a system either by reflection of the wave or by absorption and dissipation of the radiation power inside the material [5]. Metal

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based compositions are regarded as the traditional and common material owing to high

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electrical conductivity. However, they are limited due to the disadvantages such as high density, high reflectivity, corrosion susceptibility, weight penalty and difficult processing [6]. In order to achieve good performance and multifunction, various alternative candidates have been extensively researched such as intrinsically conducting polymers (e.g.

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polyaniline, polypyrrole, polythiophnes and their analogues) [7, 8], carbon materials (e.g. graphite, carbon black, graphene, carbon nanotubes, carbon fiber) [9, 10], dielectric or magnetic materials (e.g. ferrites or titanates), and their hybrid materials [11, 12]. Saini et al.

EP

[13] prepared processable aniline copolymers with 2-alkylanilines which obtained the EMI

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SE value of -23.2 dB in microwave range. Intrinsically conducting polymers exhibit tunable electrical conductivity and dielectric properties, whereas there is still maintained a distance from commercial utility due to high price and difficult processing. Li et al. [14] fabricated single-walled carbon nanotube (SWNT)-epoxy composites and the results indicated that SWNT could be used as effective lightweight shielding material. Saini et al. [15] prepared composite absorbers by incorporating of BaTiO3 or Fe3O4 nanoparticles within polyaniline, and the absorbers gained better impedance matching with dielectric and

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ACCEPTED MANUSCRIPT magnetic components. However, nanomaterials were suffered from the irreproducible results/properties mainly owing to poor dispersibility and high percolation threshold in matrix.

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The excellent mechanical and electrical properties of carbon fiber (CF) and the low density and good corrosion resistance of polymer, make CF reinforced polymer composites ideal candidate for EMI shielding materials [16-23]. However, the inherently low

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compatibility between CF and polymer leads to interfacial issue, and the performance of

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composite needs to be further improved [24]. Firstly, incorporation nanoparticles with CF/polymer composites holds promise for better SE. Liu et al. [20] fabricated carbon nanotubes (CNTs) reinforced CF/pyrolytic carbon composites by precursor infiltration and pyrolysis method, and the composites obtained 70 dB shielding effectiveness (SE) in the

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X-band (8.2-12.4 GHz). Hu et al. [17] prepared carbonyl iron powder (CIP) reinforced CF flet/epoxy resin (EP) composites through vacuum bag molding. The average SE of composites had a maximum value of 53.9 dB when the mass ratio of CIP and EP resin was

EP

0.75. Hong et al. [25] synthesized propene polymer (PP) composite reinforced by 30 wt.%

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CF and 1 wt.% CNT through hot-pressing process, and the composites obtained the best SE value of 16 dB at 1.5 GHz. Although this strategy is efficient for improving SE, the poor dispersion of nanomaterials and interfacial issue are still exist. Secondly, electroplating a thin layer of metal on CF surface is an effective way. Wang et al. [26] fabricated nickel coated CF (Ni-CF) as conductive filler in silicone rubber by using an electroplating method, and the composite attained 80 dB shielding over 30-1200 MHz. Tzeng et al. [27] prepared the nickel-coated CF/ABS composites with electroless

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ACCEPTED MANUSCRIPT deposition method which gained a high EMI shielding capability over 30 dB at 1 GHz. Whereas, the complex process of this method makes it difficult to realize. Graphene, a single two-dimensional layer with the sp2 hybridized hexagonal carbon

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network, has attracted attention due to its unique properties and versatile applications such as sensor, electronics, energy storage, semiconductor and biomedicine. Particularly, graphene with ultrathin structure and effective attenuation of microwave holds a

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remarkable position in EMI shielding filed [28, 29]. Song et al. [30] prepared flexible

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multilayer graphene/polymer composite films in sandwich structure with a SE of 27 dB. Shahzad et al. [31] synthesized reduced graphene oxide (rGO) nanocomposites with sulfur doping, and the composites obtained good shielding property with low loading. Gedler et al. [32] prepared polycarbonate/graphene composites foams with a specific EMI SE of ~

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39 dB·cm3/g. Kashi et al. [33] prepared graphene nanoplatelet nanocomposites, and the effective absorbance was more than 80% when containing 15 wt.% of GNPs. Many scholars have elaborated on the work of the modified CF or rGO in EMI

EP

shielding application. However, very few reports focused on the synergistic effects of rGO

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and CF on EMI shielding characteristics of composites. Furthermore, little research has concerned the optimization of experimental conditions of CF modification. In our previous work [34], CF was modified with rGO nanosheets through electrophoretic deposition method, then different percentages of rGO-CF reinforced unsaturated polyester composites were prepared by casting molding and the electromagnetic shielding properties of composites were investigated. In order to inquire the influence of electrophoretic conditions on microstructure and electromagnetic shielding property of rGO-CF, CF was

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ACCEPTED MANUSCRIPT modified by different GO concentration, voltage and time in the present work. 2. Experimental 2.1 Materials

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T700SC CF (12 K, 1.80 g/cm3) was supplied by Toray Company, Japan. The EP resin was obtained from Yisheng Resin Factory, China. Natural graphite powder (8000 meshes, purity of 99.95%) was chased from Aladdin Industrial Corporation. Concentrated sulfuric

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acid (H2SO4), sodium nitrate (NaNO3), potassium permanganate (KMnO4), hydrogen

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peroxide (H2O2), and ammonium hydrogen carbonate (NH4HCO3) were of analytical grade and purchased from Sinopharm Chemical Reagent (Shanghai, China). Sodium borohydride (NaBH4) was obtained from Zhanyun chemical Co., Ltd (shanghai, China). 2.2 Preparation of GO

Hummers method [35].

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The GO was synthesized by chemical exfoliation of flake graphite through modified

2.3 Electrophoretic deposition

EP

The electrophoretic deposition method was applied to introduce GO sheets on CF

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surface [36, 37]. The electrolytic treatment system of a potentiostat/galvanostat analyzer was established with CF which was used as the working electrode (positive), and graphite cathode was served as the counter electrode. Firstly, the electrochemical corrosion process was implemented to remove the commercial sizing agent and ensure the interfacial adhesion of GO nanosheets/CF. Virgin CF was treated in the electrolyte solution of NH4HCO3 (1.3 mol/L) at a direct voltage of 3 V for 5 min, and then washed by distilled water twice to remove residual electrolyte solution. Secondly, the GO sheets were

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ACCEPTED MANUSCRIPT deposited on CF surface (GO-CF) by different experimental conditions. The concentration of GO suspension, electrodeposition time, and electrodeposition voltage were classified as variables.

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2.4 Chemical reduction of GO-CF The rGO-CF was obtained by chemical reduction. The reduction process was performed at 80 °C with 50 mmol/L NaBH4 solution (pH 12) for 3 h. The rGO-CF treated

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by different time and voltage denoted as rGO-CF20, rGO-CF40, rGO-CF60, rGO-CF80,

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rGO-CF12, rGO-CF15, rGO-CF18, rGO-CF21, respectively. 2.5 Sample preparation of composites

In order to investigate the effects of electrophoretic conditions on electromagnetic properties of composites, the rGO-CF/EP composite samples were prepared by casting

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molding method. The electrophoretic conditions of the composite samples are listed in Table 1. For the composite production, rGO-CF was cut to 3-5 mm and dispersed in resin system through ultrasonic treatment, and then excluded the bubble from resin system by

EP

vacuum pumping for 30 min. The mixed resin system was EP and triethylene tetramine

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with mass ratio 100:13, and the mass fraction of fiber in resin system was 0.50%. Finally, the composites were cured in the air for 24 h and were posted cured at 80 °C for 4 h. The specimen size for EMI SE measurement was 22.86 mm× 10.16 mm× 6.00 mm. The schematic diagram of composite sample preparation process is presented in Fig.1. 2.6 Characterizations Scanning electron microscopy (HITACHIS-2500 SEM system) was used to investigate the surface morphology of rGO-CF. A Nicolet 380 infrared spectrometer

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ACCEPTED MANUSCRIPT (Thermo electron corporation, United States) was employed to characterize the chemical functional groups of CF, GO-CF and rGO-CF. The specimens were prepared by potassium bromide pellet technique.

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The complex relative dielectric permittivity and magnetic permeability were obtained by measuring the scattering parameters (S-parameters) over a frequency range of 8.2-12.4 GHz using a Vector Network Analyzer (Agilent N5234A). The final results were averaged

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data measured for five waveguide blocks of each sample.

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The EMI shielding material attenuates EMI radiation through three mechanisms: absorption (SEA), reflection (SER) and multiple-reflection (SEM), and the total SE is defined in equation [38, 39]: SE (dB) =SEA+SER+SEM

(1)

SE=SEA+SER.

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SEM can be ignored if SEA is higher than 15 dB [19]. So SE can be expressed as

S-parameters representing reflection and transmission coefficients are used to

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calculate the transmittance (T), reflectance (R), and effectively absorbance (Aeff) of the

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shielding material. The shielding by SEA and SER are dependent on T, R, and Aeff. Therefore, the SE is defined as followed equations [39]: T=S122=S212

(2)

R=S112=S222

(3)

Aeff =(1-R-T)/(1-R)

(4)

SEA=-10log(1-Aeff)

(5)

SER=-10log(1-R)

(6)

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ACCEPTED MANUSCRIPT 3. Results and discussion 3.1 The morphology and structure of rGO-CF The surface topographies of CF and rGO-CF treated with different GO concentration

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are shown in Fig. 2. Pristine CF presents a smooth surface which can be seen in Fig. 2a. After electrophoretic deposition and chemical reduction of GO-CF, wrinkled rGO sheets are deposited on CF surface in varying degrees. It can be found that only tiny rGO sheets

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are deposited on CF surface when the GO concentration was 1.0 mg/mL (Fig. 2b and 2c).

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When the GO concentration increased to 1.5 mg/mL (Fig. 2d and 2e), large amount of rGO sheets are covered on CF surface. However, when the GO concentration increased to 2.0 mg/mL (Fig. 2f and 2g), the rGO sheets stack together and the number of rGO sheets drop significantly. The stacked rGO sheets caused by the agglomeration of GO were easily

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washed off by distilled water. In general, 1.5 mg/mL was the optimal GO concentration for electrophoretic deposition process. 3.2 FTIR analysis

EP

The CF, GO-CF, and rGO-CF were characterized by FTIR. It can be seen in Fig. 3

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that few bands present in CF spectra due to its hydrophobic nature and inertia. As to GOCF, there is a broad peak located at 3400 cm-1 originated from stretching vibrations of -OH, which suggests the hydroxyl or absorbed H2O in the sample. The bands at 1762 cm-1 and 1623 cm-1 belong to the C=O stretching vibrations of carboxyl and C=C bond of carbon skeleton, respectively. The bands at 1056 cm-1 and 1382 cm-1 originate from stretching vibrations of C-O bonds of epoxy group [36]. All these bands indicate that GO sheets were successfully immobilized on CF. After treated by NaBH4, the peak at 1762 cm-1 almost

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ACCEPTED MANUSCRIPT disappears on rGO-CF curve and the intensity of other bands are weakened, which indicates that large amount of oxygen-containing functional groups were removed from GO. The result confirms that GO sheets were partially reduced during chemical reduction

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process, which was accordant with the XPS and Raman analyses in our previous work [34]. 3.3 EMI shielding property

3.3.1 EMI SE of the composites with different electrodeposition time

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Fig. 4 shows the EMI SE of rGO-CF/EP composite in X-band frequency range. It can

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be seen in the Fig. 4a that pristine EP exhibits poor shielding property (0-2.5 dB) at X-band, while all fiber reinforced composites present SE values higher than 20 dB. The improvement of SE value is attributed to the conducting network formed by chopped CF and large amount of charge carriers provided by deposited rGO sheets. Conducting

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network establishes bridges for moving mobile charge carriers which can interact with electromagnetic field [40].

With the increase of deposition time, the SE value of composites increases

EP

considerably. It is noteworthy that SE value of rGO-CF60/EP achieves 34.1 dB at 12.4

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GHz, which has a 47.6% increase than that of CF/EP (23.1 dB). This is because the extension of time was beneficial to GO immobilization which could not only strengthen the combination between CF and rGO also increase the thickness of rGO, eventually leading to better interface layer of composites. Furthermore, the introduction of rGO sheets on CF surface improved the EMI shielding property of CF/polymer composites [34, 41-46]. However, the SE value decreases to 32.5 dB at 12.4 GHz when deposition time increased to 80 min. Redundant electrophoretic time may lead to weak combination between fiber

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ACCEPTED MANUSCRIPT and resin which can be certified by the microstructure of rGO-CF80/EP in Fig. 5. Fig. 4b and c show the SEA and SER of composites. CF/EP has a SEA of 20.6 dB at 12.4 GHz. After CF modification, the absorption loss of composites increases to 24.8, 31.5,

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30.8 and 29.7 dB, respectively. SER of CF/EP is 3.1 dB at 8.2 GHz, and the value of SER of rGO-CF60/EP composites is 4.7 dB. SEA increases with the frequency significantly and SER shows a downward trend. It also can be seen in the Fig. 4d, most of EMI shielding

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comes from the absorption loss of composites, and the growth rate of the SEA is faster than

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SER with the time increasing. Based on the results, it can be concluded that the absorption was the primary EMI shielding mechanism of rGO-CF/EP composites. Furthermore, rGO sheets between CF and EP resin made contribution to the improvement of absorbing ability. Fracture surfaces of rGO-CF/EP composites with different electrophoretic time were

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analyzed and compared to that of CF/EP. As can be seen in Fig. 5a, CFs are pulled out from resin and exhibit a smooth surface, which reveals that the low adhesion condition and the interfacial debonding were the dominant failure mechanism in CF/EP [47]. When

EP

introducing rGO sheets on CF surface, the substantial chemical affinity between fiber and

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resin is presented, which is evidenced by the presence of resin residual on the surface of CF after pulled-out. It is observed that the amount of residual resin on the surface of CF increases when the electrophoretic time increased from 20 min to 60 min. The development of composite interface was ascribed to the wrinkled rGO sheets which were beneficial for the interfacial interlocking between fiber and resin. However, when the electrophoretic time increased to 80 min, the fiber surface becomes smooth and the residual resin becomes less, which implied the relative weak interface between fiber and

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ACCEPTED MANUSCRIPT resin. This phenomenon is tentatively attributed to the fact that overmuch GO sheets were coated on CF surface during EPD process, whereas cohesion between GO sheets and CF might be weaker and GO sheets were easily peeled-off from CF surface.

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To better understand the shielding performance of rGO-CF/EP with different electrophoretic time, the frequency dependence of complex permittivity and permeability are presented in Fig. 6. It can be seen that both real and imaginary part of permittivity of

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rGO-CF60/EP are the highest among all composites, in support of the high dielectric loss

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responsible for shielding property of composite. Moreover, the curves of ε” shows several minor fluctuations in the high frequency range, exhibiting an obvious frequency-dependent dielectric response. This may arise from the lag of the induced charges to follow the reversing external field at high frequencies and finally causes a reduction in the electronic

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oscillations [48-50]. However, in Fig. 6c and d, the complex permeability of all composites exhibit complex variation with no regularity, implying the components of composites have weak magnetic properties.

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The electrical conductivities (σr) of composites are calculated by the equation of

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σr≈2π f ε0ε", where f is frequency, ε0 is the permittivity of free space (ε0=8.854×10-12 F/m), and ε" is the imaginary permittivity of material [23, 51]. The σr of rGO-CF/EP with different electrophoretic time is shown in Fig. 7. As can be seen, the trend of σr according to different electrophoretic time is similar with the trend of SE value. With 60 min electrophoretic deposition, the σr of rGO-CF60/EP reaches 6.57 S/m at 8.2 GHz which has a 215.6% increase than that of CF/EP (2.08 S/m) at the same frequency. This result indicates that the introduction of rGO on CF can effectively improve the electric

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ACCEPTED MANUSCRIPT conductivity, and the influence of electrophoretic time on electric conductivity gets the same trend with that of shielding properties. 3.3.2 EMI SE of the composites with different electrophoretic voltage

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The electrophoretic time was set to 60 min and the voltage varied from 12 V to 21 V. The shielding properties of rGO-CF/EP with different voltage are presented in Fig. 8. In Fig. 8a, the CF/EP has a SE of 23.1 dB at 12.4 GHz. The SE values of the composites

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reach 23.3 dB, 34.1 dB, 33.9 dB and 37.6 dB at 12.4 GHz, corresponding to the voltage of

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12 V, 15 V, 18 V, 21 V. The comparison of our work and other literatures are shown in Table 2 [17, 20, 25, 27, 30, 52-55]. The improvement of shielding property is attributed to the high voltage which promoted the immobilization of rGO sheets on CF surface. The voltage affected the rate of GO diffusion in the solution and thus the electrolysis efficiency

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[57, 58]. High voltage was beneficial to the Kinetic rate of system, and the rate of negative charge (GO platelets) migrating toward the positive electrode (CF) was improved. Therefore, during the same electrophoretic time, more rGO sheets were coated on CF

EP

under high voltage. Large amount of rGO gave rise to large charge carriers which could

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interact with external electromagnetic wave. Fig. 8b and 8c show SEA and SER of composites. The absorption and reflection losses of CF/EP are 17.3 dB and 3.1 dB at 8.2 GHz, respectively. After electrophoretic process with different voltage, the absorption losses of composites increase to 21.1 dB, 27.9 dB, 29.6 dB and 31.9 dB; while the reflection losses achieve 2.8 dB, 4.7 dB, 3.8 dB and 4.3 dB at the same frequency, respectively. In addition, SEA shows upward trend with the frequency and SER shows downward trend. These results support the conclusion that the absorption is the primary

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ACCEPTED MANUSCRIPT shielding mechanism of rGO-CF/EP composites discussed above. The electrical conductivity of rGO-CF/EP with different electrophoretic voltage is shown in Fig. 9. The σr of composites increases with electrophoretic voltage, which has a

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same trend of SE value. The maximum value of 7.20 S/m at 8.2 GHz is obtained with the electrophoretic voltage of 21 V. This result indicates that electrophoretic voltage affects the electrical conductivity of composites, which is associated with the shielding property.

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4 Conclusions

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In this paper, rGO-CF was prepared through electrophoretic deposition process with different electrodeposition conditions and subsequent chemical reduction. The rGO-CF/EP composites were prepared and the effects of three electrodeposition variables on the electromagnetic properties of the composites were studied systematically. The results

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showed that the optimal concentration of GO solution was beneficial to the combination between graphene nanosheets and CF. The SE of composites increased from below 25.0 dB to 37.6 dB by varying electrophoretic time and voltage. With 21 V and 60 min

EP

electrophoretic deposition, the SE of rGO-CF/EP21 was 37.6 dB at 12.4 GHz, which

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implied that rGO-CF composite can be used as a light-weight and high-efficiency shielding material.

Acknowledgments

This work is supported by Special Program for Independent Innovation and Achievements Transformation of Shandong Province, China (Grant No. 2014ZZCX05302), and the major special project of science and technology in Shandong province, China (Grant No. 2015JMRH0110).

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band frequency range. Electromagnc C 1992;34(4): 478-481. [39] Hong YK, Lee CY, Jeong CK, et al. Method and apparatus to measure electromagnetic interference shielding efficiency and its shielding characteristics in broadband frequency ranges. Rev Sci Instrum 2003;74(2):1098-1102.

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Mater 2004;16(5):401-405. [43] Wang C, Han X, Xu P, et al. The electromagnetic property of chemically reduced graphene oxide and its application as microwave absorbing material. Appl Phys Lett

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[46] Wen B, Wang X, Cao W, et al. Reduced graphene oxides: the thinnest and most lightweight materials with highly efficient microwave attenuation performances of the carbon world. Nanoscale 2014;6:5754-5761.

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nanoplatelets and short glass fiber on the mechanical and interfacial properties of epoxy composites. Compos Sci Technol 2014;98:15-21.

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7689. [51] Shi X, Cao M, Fang X, et al. High-temperature dielectric properties and enhanced temperature-response attenuation of nanorods. Appl Phys Lett 2008;93:223112.

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properties of carbon fiber/graphene nanosheets/epoxy composite. Polym Composite

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2013;60:379-391.

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incorporating carbon black. J Polym Res 2015;12:158.

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ACCEPTED MANUSCRIPT fibers. Compos Sci Technol 2016;126:149-157. Figure Captions Fig. 1 Schematic diagram of composite sample preparation process

1.0 mg/mL, (d, e) 1.5 mg/mL, (f, g) 2.0 mg/mL Fig. 3 The FTIR spectra of CF, GO-CF, and rGO-CF

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Fig. 2 The surface topographies of rGO-CF with different GO concentration: (a) CF, (b, c)

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Fig. 4 (a) SE, (b) SEA, and (c) SER of composites with different electrophoretic time, and

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(d) the distribution of SE at 12.4 GHz

Fig. 5 The interface microstructure of (a) CF, (b) rGO-CF20, (c) rGO-CF40, (d) rGO-CF60, (e) rGO-CF80 with EP matrix

Fig. 6 The complex permittivity and permeability of composites with different

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electrophoretic time

Fig. 7 The electrical conductivity of composites with different electrophoretic time Fig. 8 (a) SE, (b) SEA, and (c) SER of rGO-CF/EP composites with different

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electrophoretic voltage, and (d) the distribution of SE at 12.4 GHz

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Fig. 9 The electrical conductivity of composites with different electrophoretic voltage

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Table 1 The electrophoretic conditions of composite samples GO concentration Electrophoretic Electrophoretic Sample name (mg/mL) time (min) voltage (V) rGO-CF20/EP 1.5 20 15 rGO-CF40/EP 1.5 40 15 rGO-CF60/EP 1.5 60 15 rGO-CF80/EP 1.5 80 15 rGO-CF12/EP 1.5 60 12 rGO-CF15/EP 1.5 60 15 rGO-CF18/EP 1.5 60 18 rGO-CF21/EP 1.5 60 21

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Author Li et al.[52]

Table 2 The comparison of our work and other literatures Frequency Thickness Material Addition (GHz) (mm) 0.4wt.% GNSs GNSs/epoxy/CF 2-20 1 63-65 vol.% CF

SE (dB) 60-70

PP-CF

10 vol.%

8-12

3.2

25

Song et al.[54]

PVDF/PETG/CF/ CB

5 wt.% CB

1.5

4

30

Wong et al.[55]

Recycled CF veils

Double layers

0.4

---

70

Song et al.[30]

Graphene/EVA

60 vol.%

8-12

0.35

15

Hu et al.[17]

CIP/CF/EP

8-12

4

53.9

Hong et al.[25]

CNT/CF/PP

1.5

1

16

Liu et al.[20]

Ni-CNT-C/C

5.0 wt.%

8-12

2

75

Tzeng et al.[27]

ENCF/ABS

12-14 vol.%

1

---

30

This work

rGO-CF/EP

0.50 wt.%

8-12

6

37.6

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0.75 wt.% CIP 0.75 wt.% CF 1wt.% CNT 30 wt.% CF

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Ameli et al.[53]

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Fig. 1 Schematic diagram of composite sample preparation process

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Fig. 2 The surface topographies of rGO-CF with different GO concentration: (a) CF, (b, c) 1.0 mg/mL, (d, e) 1.5 mg/mL, (f, g) 2.0 mg/mL

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Fig. 3 The FTIR spectra of CF, GO-CF, and rGO-CF

Fig. 4 (a) SE, (b) SEA, and (c) SER of composites with different electrophoretic time, and (d) the distribution of SE at 12.4 GHz

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Fig. 5 The interface microstructure of (a) CF, (b) rGO-CF20, (c) rGO-CF40, (d)

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EP

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rGO-CF60, (e) rGO-CF80 with EP matrix

Fig. 6 The complex permittivity and permeability of composites with different electrophoretic time

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Fig. 7 The electrical conductivity of composites with different electrophoretic time

Fig. 8 (a) SE, (b) SEA, and (c) SER of rGO-CF/EP composites with different electrophoretic voltage, and (d) the distribution of SE at 12.4 GHz

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Fig. 9 The electrical conductivity of composites with different electrophoretic voltage