graphene composites for electromagnetic shielding

graphene composites for electromagnetic shielding

Materials Chemistry and Physics 232 (2019) 246–253 Contents lists available at ScienceDirect Materials Chemistry and Physics journal homepage: www.e...

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Materials Chemistry and Physics 232 (2019) 246–253

Contents lists available at ScienceDirect

Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys

Lightweight sandwich fiber-welded foam-like nonwoven fabrics/graphene composites for electromagnetic shielding Liangsen Liu, Haibo Wang, Mingjing Shan **, Yaming Jiang, Xingxiang Zhang, Zhiwei Xu * Tianjin Municipal Key Laboratory of Advanced Fiber and Energy Storage Technology, School of Textiles, Tianjin Polytechnic University, Tianjin, 300387, China

H I G H L I G H T S

G R A P H I C A L A B S T R A C T

� Nonwoven fabrics with sandwich and welding-network microstructure was first designed and manufactured. � Exceptional shielding effectiveness (23103.4 dB cm2 g 1) and mechanically robust with tensile MPa of 349 was achieved. � Multiple reflection effect should not be neglected in the ultrathin material.

A R T I C L E I N F O

A B S T R A C T

Keywords: Sandwich microstructure Welding-network Nonwoven fabric Electromagnetic interference shielding Mechanical properties

With the remarkable increment speed of consumer electronics, shielding materials qualified for favourable minimal thickness, mechanical behaviors and efficient conduction path are imperiously demanded. To manu­ facture desired shielding materials qualified for favourable mechanical behaviors and efficient conduction path, we designed a foam-like nonwoven multiscale composite with welding-network, sandwich and random orien­ tation combined architectures for the first time. A 0.5-mm-thick epoxy composite exhibits an outstanding shielding effectiveness of 65 dB, and the specific electromagnetic interference shielding effectiveness reaches to ~23103.4 dB cm2 g 1, which surpassed that in reported literature. The continuous backbone with sandwich microstructure enables the epoxy composites to be mechanically robust with the tensile MPa of 349. The exceptional mechanical performance exhibited an alternative approach to exploit potentials of carbon fiberbased nonwoven fabrics for developing advanced multifunctional materials.

1. Introduction In recent decades, the extensive usage of electrical equipment and portable electronics leads to serious electromagnetic interference (EMI) pollution [1,2]. A high-performance EMI shielding material with a broadband EMI ability is necessary to remove adverse electromagnetic

waves availably in civil, healthcare, and military applications [3]. Car­ bon nanofillers, such as carbon nanotubes, carbon fibers and nano­ graphene sheets, have been widely utilized to form electrically conducting networks in polymer matrices [4,5]. In their polymer com­ posites, nevertheless, several conductive active carbon enhancers were randomly dispersed inside substrates. It was possible to result in the

* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (M. Shan), [email protected] (Z. Xu). https://doi.org/10.1016/j.matchemphys.2019.04.085 Received 23 February 2019; Received in revised form 2 April 2019; Accepted 29 April 2019 Available online 3 May 2019 0254-0584/© 2019 Elsevier B.V. All rights reserved.

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disorder and agglomerate condition for active carbon enhancers and the reduced performance of polymer composites. Commonly, the high po­ tency of carbon enhancers (>10 wt %) in polymer substrates was inte­ grant to constitute effective conductive paths and acquire an desired shielding effectiveness (SE) (>20 dB) [6]. To further decrease the con­ tent and develop the shielding ability, researches focus on devising the three-dimensional (3D) interconnected porous structures for prepara­ tion of functional composites [7–9].3D network structures show rela­ tively better performance compared with non-network materials, however, there are no breakthrough designs to date [10,11]. Recently, nonwoven fabrics fabricated by bonding synthetic fibers together to form a nonwoven network have attracted great interest in energy-related applications [12,13].However, the bottleneck is that carbon fiber nonwoven fabric can not form a complete and effective conductive network due to conventional single lap adhesive bond structure among them, which limits transmission of electromagnetic wave from one fiber to the other, and there is adverse condition for EMI shielding performance. Welding is a reliable connection methodology in modern manufacturing processes, which can firmly connect two or more workpieces of the same or varied constitutions to achieve the complete interfacial coalescence. Hence, nonwoven fabrics with welding-network provided a more effective highway for electron transport and better electrical conductivity. It is well known that the EMI SE relied on not just the intrinsic electrical conductivity, and interfacial polarization and multiple reflection would be essentially responsible for electromagnetic energy conversion and consumption. Although the fiber-welded foam-­ like nonwoven fabric could service to practical EMI shielding, their shielding effectiveness was still limited due to the lack of optimized structure [14]. Considering these, an excellent electromagnetic shielding material was designed in this work. We designed and fabricated a non-woven multiscale composite with unique welding-network and sandwich combined architectures by assembling the graphene oxide (GO) sheets on fiber-welded foam-like nonwoven fabric. The central idea was that GO acted as the “cuticular layer” covering on the nonwoven weldingnetwork, which enabled foam-like nonwoven fabric to assemble into sandwich microstructure. Also, the combined fiber-welded foam-like nerwork and sandwich microstructure provided epoxy composites with favourable EMI-shielding efficiency and mechanical properties.

2.2. Fabrication of sandwich fiber-welded nonwoven fabric/GO architecture Graphite oxide was prepared by referring to our previous literature [2,15,16]. The GO sheets were uniformly dispersed in deionized water via ultrasonication processing, which was beneficial to form a homo­ geneous suspension for electrophoretic deposition process [17].The NF, as the deposition electrode, was put between the two metallic electrodes with 9 cm space. Ultrasonication was operated before each electropho­ retic deposition process for expanding the space between NF as well as to eliminate the tiny bubbles resulting from water electrolysis, which also could help to acquire a homogeneous distribution of GO on NF and the amount of GO deposited onto NF was controlled by deposition time. In this experiment, the deposition time was ranged from 30 to 120 s. We made GO/NF (GNF) samples with acronym in Table 1. 2.3. Production of composite samples The manufacture of GNF/epoxy composites referred to the following procedure: the NF materials were firstly laid over a mold. Then the prepared matrix including epoxy, curing agent and accelerant was infused into the sealed mold under resin transfer molding process. The matrix in the container was maintained at a constant delivery pressure (0.1 MPa). Resin was infused at a flow rate of 3 cm3/s, and this process required to vacuum assistance. Finally, the mold with GNF and resin was transferred to oven for curing, following the solidification procedure. The final NFs/epoxy composites were tailored and polished for me­ chanical and shielding experiments [18,19]. 2.4. Characterizations Microstructure of NF and GNF was detected with scanning electron microscope (SEM), interpreting as FE-SEM of Hitachi G-400. The chemical composition of NFs was measured by Raman spectroscopy (LABRAM-HR confocal laser micro-Raman spectrometer). EMI shielding properties of the GNF/epoxy composites with the diameter of 8 cm were measured in scopes from 30 MHz to 3 GHz by a ZNB40 vector network analyzer. Flanges were used as an continuous conductor holder to both secure the sample and capacitively couple the conductors, as shown in Fig. S3. The inner conductor of this type is 3.2 cm in diameter, while the outer flange has inner and outer diameter dimensions of 7.6 and 13.3 cm, respectively. The scattering parameters (S11 and S21) were named to calculate the reflected power (S11), transmitted power (S21), EMI SE (SETotal), microwave reflection (SER) and microwave absorption (SEA), using the following equations [14].

2. Materials and characterizations 2.1. Materials Natural graphite flakes with the diameter of 50 μm were used. Fiberwelded nonwoven fabric was obtained from Japan Toray Industries. Epoxy value for modified epoxy (JC-02) is 0.51–0.53 and modified 2ethyl-4-methylimidazole (JH-0511) was utilized as accelerant, obtain­ ing from Changshu Chemical Co. Ltd., China. Nonwoven fabric was obtained from Japan Toray Industries, which was made of poly­ acrylonitrile carbon fiber.

SER ¼ 10Lg

SEA ¼ 10Lg

1 1

1 � 2 �S11 j

(1)

� 2 �S11 j � 2 �S21 j

(2)

SETotal ¼ SER þ SEA

(3)

3. Results and discussion 3.1. Physiochemical structure of NF and GNF

Table 1 The acronym of samples. Sample number

GO concentration (mg/mL)

Electrophoretic time(s)

Electrophoretic Voltge(V)

NF GNF GNF GNF GNF

1 1 1 1 1

0 30 60 90 120

24 24 24 24 24

-1 -2 -3 -4

As could be seen in Fig. 1a, the NF was in formation of 3D inter­ connected long carbon fiber, and both carbon fibers were random ori­ ented and physically interconnected together, thus establishing an interwoven reticulated architecture. For the composites with conductive network, the electrical conductivity is greatly relevant to electron transport distances and the amount of fiber-fiber bonding points [20]. The image of NF network exhibited the contacts between individual fiber to be welded together, providing highly effective electric channel 247

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Fig. 1. SEM and TEM images of NF (a–b); GNF (c–e). Distribution of C and O element (measured by mapping scanning spectra) of NF (f) and GNF(g).

welding-network could be precisely noticed below the thin“cuticular layer”. From the transmission electron microscope image, the thin“cu­ ticular layer” was demonstrated to be multiple layers of GO sheets. Furthermore, C and O elemental mapping had been provided in order to observe distribution of element (Fig. 1f and g). Although multilayered graphene was not as conductive as few-layer graphene, it showed further more structural imperfections and doughty charge polarization ability owing to its particular electronic properties, for instance extremely supernal electron-transfer rates. In consequence, these might boost electromagnetic wave attenuation when sustained to an commutative electromagnetic area [4]. To investigate the functional GO layer number, Raman spectra were measured and shown in Fig. 2. It is known that three prominent bands appear in the Raman spectrum of graphene: D band at about 1357 cm 1, the G band at about 1591 cm 1 and the 2D (G0 ) band around 2650 cm 1. The D band is a defect or disorder, which is caused by introducing sp3 carbon originating from a double resonance Raman process [44, 45], whereas the G band origi­ nating from in-plane vibration of sp2 carbon atoms is a doubly degen­ erating phonon mode. The 2D band provides the information on the electronic structure of graphene through the double resonance process. It has been demonstrated that the GO layer number could be calculated by the constituent analysis of the 2D peak, which deems different dedication to the transfer of Raman parameters hinging on multilayer or single layer GO. As the number of layers of GO increased, the strength of 2D peaks began to be lower than that of the D peak and peak intensity of 2D band shifted to the long wavelength sides(Fig. 2). [21] To further explain the influence of “cuticular layer” on mechanical capacity, the concrete analysis of wetting angle measurements had been carried out afterwards. The interfacial bond between GNF and epoxy was a key factor to final performances, and it was analyzed by the contact angle measurements [22,23]. The pristine NF has the high initial contact angle of 85� from

Fig. 2. Raman spectra of NF and GNFs.

for electrons, therefore guaranteeing its preferable electrical conduc­ tivity. Pristine NF presented a smooth surface and a number of super­ ficial parallel trenches were shown along with fiber axis (Fig. 1b). After assembling the GO sheets onto the NF welding-network, GO acted as the “cuticular layer” covering on the NF welding-network, which empow­ ered foam-like nonwoven fabric to assemble into sandwich microstruc­ ture. The SEM images with high-magnification further found clearly that winkles and crinkles of the multiple layer GO sheets were constituted on the NF welding-network (Fig. 1c and d). The profile of NF 248

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3.2. Mechanics properties and enhancement mechanism of NF and GNF composites To identify the function relationship between GNF and mechanical properties, tensile performance for composites has been tested. A speed extension measurement (5 mm/min) for NF/epoxy, GNF-1/epoxy, GNF2/epoxy, GNF-3/epoxy and GNF-4/epoxy composites was also statisti­ cally analyzed. The strength of NF/epoxy composites was also observ­ ably influenced by the interfacial adhesion ability [25,26]. Owing to presence of the GO interface, more active sites enhanced effectively the wettability between NF and epoxy to form uniformly composites. Along with GNF-1, GNF-2, GNF-3 and GNF-4 in isotropic arrangements, they could constitute multi-layer interface connection between fibers and epoxy in the direction of mechanical experiments. In our previous work, we has found that GO-based interface layer could improve the load transfer from epoxy to reinforcement and decrease interfacial stress concentrations [19,26–28]. The ample oxygen-containing groups on GO offered good compatibility for NF with the polar epoxy. Therefore, the adhesion between the GNF and epoxy was in the positive effect, which was conducive to accelerating load transfer. Under the circumstances, stress concentration could be avoided effectively and the exfoliation of reinforcements from epoxy might be significantly weakened [29,30]. It could be observed that both stress and strain of specimens were increased. It was remarkable that tensile strength of GNF/epoxy ach­ ieves 349 MPa, which had an increase of 36.3% in comparison to NF/epoxy composites(Fig. 4). GO sheets assembling on both side of NF network formed the “cuticular layer” to establish sandwich micro­ structure. The “cuticular layer” acted an crucial role in tensile property. One side, the “cuticular layer” served as constraint agent in certain di­ rection that was perpendicular to the force direction, and the schematic diagram was illustrated in Fig. 5 (blue line). Thus, some longish or loose fibers in GNF network would be confined during tensile course, which made the fracture surface of GNF quietly other from that of NF network. Besides, as was illustrated in Fig. 5, the “cuticular layer” could furnish shear stress and promote force of friction (black line) between the “cuticular layer” and the “welded-networks”, which ascribe to sectional resistance in the tensile course [13]. Meanwhile, the strength of GNF/epoxy composites was also observably influenced by substrate architectures and interface infiltration capability. The oxygen functional groups in GO make GNF be hydrophilic and compatible with organic polymers [28,31]. In general, this could be sumed up that both inter­ phase infiltration competence and sandwich microstructure acted an crucial role in perfecting the tensile strength of GNF composites. The external loads could be validly transferred by sandwich microstructure and the favourable interphase. However, the tensile strength of GNF-3/epoxy was cessation of increase compared with that of GNF-2/epoxy as expected. The results could be owing to facts that ag­ glomerations of GO were anticipated to sever as imperfections in the interfacial regions, which overrode stress transferring effects for the

Fig. 3. Epoxy contact angle of (a–b) NF and (c–d) GNF-2.

Fig. 3a and b. When “cuticular layer” assembled on the NF welding-network, a distinct tendency could be observed that values of epoxy contact angle gradually reduced (Fig. 3c and d), which distinctly enhance the epoxy infiltration ability, rendering the impregnation pro­ cess much easier [24].For the favourable interface area with medial modulus could act as strain mediated transports, which might attain the synergistic improvement of interfacial interlocking. Previous researches have also exemplified that GO sheets have active effect on polymer substance owing to the ample oxygen-containing functional groups. This suggested GNF could enhance the interfacial interaction compared with NF. However, when the GO layer number reached a certain thickness, the contact angle stopped falling. So GNF-3 and GNF-4 present the similar contact angle as the GNF-2.

Fig. 4. Tensile strength (a) and tensile stress-strain curves (b) for epoxy nanocomposites filled with NF (black line) and GNF-2 (red line). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.) 249

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Fig. 5. Schematic diagram of NF and GNF network deformation during tensile process. Table 2 Comparison of EMI shielding performance of polymer nanocomposites. Filler type

Content (wt%)

Thickness [cm]

EMI SE [dB]

Frequency

Ref.

Graphene foam/ PDMS rGO-CF/ epoxy

0.8

0.1

30 20

30 MHz–1.5 GHz 8–12 GHz

[30]

0.50% rGO, 21%CF 0.66 wt % 2 wt% 2 wt%

0.66

37.6

8–12 GHz

[31]

0.2 0.2

33 40

8–12 GHz

[9]

0.01

38

400–4000 MHz

[32]

0.33 wt %

0.4

35

8–12 GHz

[10]

30 wt%

0.1

44

1–10 GHz

[3]

13.3 wt %

0.017

20.3

1 GHz

[33]

20 wt%

0.45 0.0165

200–2000 MHz 8–12 GHz 50 MHz–13.5 GHz

[34]

40 wt%

30 40 27

15 wt% 0.5 wt%

0.15 0.05

15–20 71

500 MHz–1.5 GHz 1–3 GHz

[36] This work

CNT sponge/ epoxy Aligned RGO/ epoxy Graphene aerogels/ phenolic/ resol resin Carbon black/ epoxy Carbon nanotube/ cellulose SWNT/ PMMA MWNT/ PMMA SWNT/epoxy GNF/epoxy

Fig. 6. Plots of EMI SE versus frequency for epoxy nanocomposites filled with NF and GNF.

interface [32,33]. 3.3. EMI shielding efficiency of NF and GNF composites To analyze the EMI shielding properties of GNF/epoxy composites, EMI-shielding properties were measured in the frequency range of 1–3 GHz and compared with those of NF epoxy composites (Fig. 6). Electromagnetic waves can be attenuated quickly in a good conductor because of the induced current created in the conductor. Thus, shielding materials need to be electrically conductive. Also, interfaces within the shielding material are strongly needed, which can result in multiple scattering to absorb more electromagnetic waves. The welding-network provided a more effective highway for electron transport and the EMI SE value for NF composites reached to 45 dB, suggesting that these could be primarily ascribed by the conductive path in the matrix. Besides, interphase inside shielding materials was another significant influence factor and it was also resulted from impedance polarization loss and multiple internal reflections. In this GNF composites, the GO sheets significantly strengthened the loss of surface currents via broadening conductive networks and bringing ample interfaces in the matrix. In addition, the sandwich microstructure and ample interphases in the GNF composites could improve the reflection and absorption result further [34]. The EMI shielding effectiveness increase from 45 dB to 65 dB with an average thickness around 0.5 mm. The reported average values of EMI SE floated between the scope of 15 50 dB for carbon-based rein­ forced polymer composite and our GNF sandwich microstructure demonstrated one of the super-high shielding performances, indicating

[35]

*PDMS: polydimethylsiloxane, PMMA: polymethyl methacrylate.

that it has great potential to serve EMI shielding application. Specific EMI shielding effectiveness values were proposed to objectively evaluate the shielding performances, especially when both the thickness and density of materials were intervened. After taking these into consider­ ation, absolute effectiveness value could achieve ~23103.4 dB cm2 g 1. Table 2 compares the EMI SE performances of GNF/epoxy nano­ composites with those of carbon fiber-based nonwoven fabric, graphene and carbon nanotube-based polymer composites which were published in the previous literature. Clearly, our GNF/epoxy composite obviously displays well-satisfied SE value. It was well established that materials with high conductivity was superior in EMI shielding. The conductivity of high defect density was found to lag behind those of former one by 3 orders of magnitude, predominantly as a consequence of lattice vacancies that nanometersized graphitic domains were separated by defect clusters, which resulted in hopping conduction. The electrical conductivity of NF/ 250

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enhanced EMI performance compared with NF composites. Moreover to the impedance match, it was demonstrated that the EMI performance was also connected with the microstructure of materials. Compared with NF, GNF composites with sandwich microstructure could simulta­ neously furnish more active patch for dispersing of electromagnetic wave and surface current loss dramatically improved via stretching the partial conductive network and bringing multitudinous interfaces in polymer matrix [36]. From the above discussions, it could be deduced that the enhanced EMI value of GNF nanostructures is ascribed to this better impedance match and special sandwich microstructure. 3.4. Theoretical calculation for SE of composites Once the electrical conductivity, σ, of composites satisfies σ ¼ σac þ σdc ≫ 2πfε0 (where σac, σ dc and ε0 ¼ 8.854 � 10 12 F/m are the alter­ nating current conductivity, the direct current conductivity and the vacuum permittivity, respectively), the shielding effectiveness values, SEA and SER, can be theoretically estimated by the following equations which are usually applied to solid conductive materials: The reflection expression for multilayer materials is � � σac SER ¼ 10log (4) 32π f ε0

Fig. 7. Electrical conductivity of NF and GNF polymer nanocomposites.

epoxy, GNF-1/epoxy, GNF-2/epoxy, GNF-3/epoxy and GNF-4/epoxy composites was measured with the four-probe resistivity meter at room temperature by inserting four acicular probes into samples. Fig. 7 showed the electrical conductivities of NF/epoxy and GNF/epoxy composites ranged from 28 to 155S/m. The increase of electrical con­ ductivity could be contributed to the constitution of sandwich micro­ structure. The “welded-networks” with the crisscross of carbon fiber conductive network interconnection, and the existence of carbon fiber network promote the formation of conductive network. The graphene network forming “cuticular layer” benefits electrical aggregation. Two networks were mutual infiltrated and overlapped together, making epoxy resin impregnated composites keep stable and compact structure, as well as promoting the formation of good interface compatibility be­ tween GNF and epoxy resin. And then the electrical conductivity of whole epoxy composites was improved. In order to comprehend the shielding mechanisms for the much perfected EMI shielding property of GNF composites, the permittivity was especially researched. The permittivity ε0 and ε" is equivalent to the polarization ability. As a rule, the polarization is attributed to functional groups, imperfections and interphases. The real permittivity ε0 and the imaginary permittivity ε" of NF and GNF composites were analyzed in the scope of 1–3 GHz. As appeared in Fig. 8, it is found that the value of ε0 for GNF composites was significantly above that for the NF composites. This could be explained by the fact that the GO were assembled on the NF welded-network, which could enhance the electric polarization and conductivity path, since ε0 was an presentation of polarization ability for material. It incorporated dipolar and electric polarization in EMI fre­ quency [35]. Simultaneously, the same trend appeared for the value of ε". Therefore, the doughty dielectric loss of GNF composites revealed the

pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi SEA ¼ 8:68t σ ac πf μ0 μ’

(5)

where μ0 (¼ 1.257 � 10 6 H/m), μ0 , and t are the vacuum permeability, the real permeability, and the sample thickness, respectively. The alternative current conductivity is determined by σac ¼ 2πf ε0ε00 , where ε00 is the imaginary permittivity.

Fig. 9. Comparison of experimental and theoretical EMI SE for composites.

Fig. 8. The ε0 (a) and ε00 (b) for epoxy nanocomposites filled with NF (black line) and GNF-2 (red line) in the range of 1–3 GHz. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.) 251

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Because the electrical conductivity of GNF composites (over 60 S/m) was much higher than the largest value of 2πfε0 (0.67 Hz F/m) in the frequency range of 1–3 GHz, both SEA and SER were determined by the permittivity, permeability, and electrical conductivity. Fig. 9 presents the comparison of SE (SEA þ SER) between the calculation and experi­ mental data. The experimental and estimated values for NF and GNF composites demonstrated that the estimated shielding effectiveness values were not consistent with experimental results. When the electromagnetic field passes through a medium, it will reflect at the interface of the medium, and it also can be attenuated in the medium, so the shielding effectiveness SE can be written as [27]: SEðdBÞ ¼ SEA þ SER þ SEM

China (11575126, 51708409), the Petrochemical Joint Fund of National Natural Science Fund Committee - China National Petroleum Corpora­ tion (U1533123) and the Natural Science Foundation of Tianjin (16JCZDJC37800, 16ZXCLGX00090). Appendix A. Supplementary data Supplementary data related to this article can be found at https://do i.org/10.1016/j.matchemphys.2019.04.085. References

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Where SEA and SER are electromagnetic losses caused by the absorption and interfacial reflection of the materials respectively, and SEM is pro­ duced by multiple reflections within the material. The actual multiple reflection is very complex, and the multiple reflection loss can be approximately expressed as[ 28]: � � L� � SEM � 20lg�1 e 2ð1þjÞδ � (7) Where L is the shielding thickness (0.5 mm), and the calculated multiple reflections versus different frequency are obtained by calculation. The effect of multiple reflections on overall shielding performance is obvious, especially in the low frequency range. Material morphologies has a significant impact on multiple reflections and the effect of multiple reflections on the overall shielding effectiveness can be reduced by more than 6–18 dB. In this work, the calculated SE values were always lower, by over 20 dB, than the measured values because that eq (4) and eq (5) only takes electrical conductivity, permittivity, and permeability of material properties into account, while the material morphologies are also related to SE. It has been confirmed that sandwich microstructure are beneficial for EMI shielding. Multiple reflections within and between the hollow graphene tubes of graphene sheets enhanced interactions between the shielding material and EM waves. Charge delocalization between NF and the graphene sheets coating which is not taken into account is another significant contribution to SE. For thin shielding materials, therefore, multiple reflections to the overall shielding effec­ tiveness must be considered in theoretical calculations. 4. Conclusion We designed and fabricated a non-woven composite with unique welding-network and sandwich combined microstructure via assem­ bling the GO sheets on fiber-welded foam-like nonwoven fabric. This exellent performance originated from welding-network and sandwich microstructure, which providing a more effective highway for electron transport and multiple internal reflections in the fiber-welded foam-like nonwoven fabric. The EMI shielding effectiveness of sandwich GNF composites assembled by GO increased from 45 to 65 dB, compared with that of NF composites with an average thickness of 0.5 mm. And the specific EMI shielding effectiveness value could achieve ~23103.4 dB cm2 g 1, which outperformed that in reported literature. More importantly, GNF significantly increased the tensile strength by 36% more than NF. The calculated SE values were always lower than the measured values because the material morphologies were not taken into account in calculation. The purpose proposed in this work also dem­ onstrates a universal and facile route for scalable manufacture of carbon fiber nonwoven fabrics composite as lightweight, exceptional mechan­ ical and electromagnetic shielding performance in fields such as new generation of electronic devices. Acknowledgments The work was funded by the National Natural Science Foundation of 252

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