Flexible PDMS Nanocomposites Enhanced with Three-dimensional

Subscriber access provided by Kaohsiung Medical University

Applications of Polymer, Composite, and Coating Materials

Flexible PDMS Nanocomposites Enhanced with Three-dimensional Graphene/Carbon Nanotubes Bicontinuous Framework for High-Performance Electromagnetic Interference Shielding Sumin Zhao, Yehai Yan, Ailin Gao, Shuai Zhao, Jian Cui, and Guangfa Zhang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b09275 • Publication Date (Web): 10 Jul 2018 Downloaded from http://pubs.acs.org on July 11, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Flexible

PDMS

Nanocomposites

Enhanced

with

Three-dimensional

Graphene/Carbon Nanotubes Bicontinuous Framework for High-Performance Electromagnetic Interference Shielding Sumin Zhao, Yehai Yan, Ailin Gao, Shuai Zhao, Jian Cui, and Guangfa Zhang* Key Laboratory of Rubber-plastics, Ministry of Education/Shandong Provincial Key Laboratory of Rubber-plastics, School of Polymer Science and Engineering, Qingdao University of Science and Technology, Qingdao 266042, P. R. China

ABSTRACT High-performance electromagnetic interference (EMI) shielding materials featuring with light-weight, flexibility, excellent conductivity and shielding properties, as well as superior mechanical robustness are highly required yet still remain a daunting challenge so far. Here a flexible and exceptional EMI-shielding polydimethylsilane/reduced graphene oxide/single wall carbon nanotubes (PDMS/rGO/SWCNTs) nanocomposite was developed by a facile backfilling approach utilizing a preformed rGO/SWCNTs aerogel as the three-dimensional (3D) conducting and reinforcement skeleton. Pristine SWCNTs acting as secondary conductive fillers showed intriguing advantages, whose intrinsically high conductivity could be well preserved in the composites due to without surface acidification treatment. The robust and interconnected 3D network can not only serve as fast channels for electron transport but also effectively transfer external load. Accordingly, a prominent electrical conductivity of 1.2 S cm−1 and an outstanding EMI shielding effectiveness (SE) of around 31 dB over X-band frequency range were achieved for the resultant composite with an ultralow loading of 0.28 wt%, which is among the best results for currently reported conductive polymer nanocomposites. Moreover, the composite displayed an excellent mechanical properties and bending stability, such as a 233% increment in the compression strength was obtained compared with that of neat PDMS. These observations indicate the unrivalled effectiveness of 3D rGO/SWCNTs aerogel as reinforcement to endow the polymer

composites

with

outstanding

conductive and

mechanical properties

toward

high-performance EMI shielding application.

KEYWORDS: electromagnetic interference shielding, polydimethylsilane, graphene, SWCNTs, backfilling

1. INTRODUCTION Currently, with the rapid development of modern electronics, electromagnetic interference (EMI) and radiation issue has evoked extensive attention because of its harmful effects on precision

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

electronic equipment and human health1-4. Thus, great efforts have been devoted to developing various high-performance EMI shielding materials. Compared to conventional metal-based shielding materials5, the emerging conductive polymer composites (CPCs) are believed to be more promising alternatives for EMI shielding applications due to their light-weight, flexibility, resistance to corrosion, low cost, and good processability6-9. CPCs are typically consisted of polymer matrices and active conductive fillers. Except for high EMI shielding performance, light-weight and flexibility are two other crucial technical requirements for practical EMI shielding applications especially in areas including aircraft, aerospace, and fast-growing flexible electronics9. Therefore, PDMS with well mechanical properties, especially good flexibility, is an intriguing candidate as a polymer matrix. It is well established that the EMI SE of CPCs is mainly dependent on the intrinsic electrical conductivity and connectivity of the conductive fillers. Noteworthy, carbon-based materials, such as carbon fibers, graphite, especially graphene and carbon nanotubes (CNTs) have been widely utilized as conductive fillers to construct EMI shielding CPCs owing to their high electrical conductivity, light-weight, remarkable mechanical properties, and large aspect ratios6-9. Some pioneering studies have indeed confirmed the exceptional efficiency of graphene and reduced GO as conductive fillers for endowing the insulating polymers, such as polymethylmethacrylate (PMMA) and epoxy, with superior electrical and EMI shielding performances10, 11. Traditional direct blending methods are the most common processing routes to fabricate CPCs but suffer from some distinct disadvantages. For instance, the high aspect ratios and strong π-π interactions of carbon-based fillers make them easily overlap or aggregate, and thus difficult to disperse individually and uniformly inside the polymer matrix. Besides, individual carbon-based fillers are enclosed by polymer chains, leading to a high junction contact resistance between the separated filler components and hence a lower electrical conductivity. Consequently, requiring a relatively higher loading of carbon-based fillers to achieve an interconnected conductive channel in the matrix for enhancing electrical conductivity and EMI shielding performance of the composites12. Nevertheless, a high content of fillers tends to weaken the mechanical properties and processability of the polymer composites because of their severe aggregation and poor filler-matrix interaction.


Page 2 of 26

Page 3 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


To overcome the above limitation, backfilling method has been recently explored for constructing excellent CPCs. Specifically, a 3D interconnected conductive network of carbon-based fillers (such as graphene aerogels (GAs)/foams (GFs)) is preformed, followed by impregnation of polymers/monomers into the 3D scaffold. This backfilling strategy offers several prominent superiorities in comparison to blending methods6, 7, 13-16: (i) The prefabrication of 3D skeleton can not only achieve effectively uniform dispersion of carbon-based fillers, but also endow the 3D architecture with high porosity and lightweight performance. (ii) 3D interconnecting network can be formed at an extremely low filler loading, serving as fast transport channels for charge carriers and thereby provides a remarkably enhanced electrical conductivity for the composites. (iii) The numerous cell/matrix interfaces in the 3D architecture can also facilitate the attenuation of incident electromagnetic waves through multi-reflection, which further improve the EMI shielding performance. Based on above principles, some GAs or GFs have been prepared by chemical vapor deposition (CVD)7-9, 16, 17, self-assembly13, 18, or template-assisted assembly6, and their polymer composites were further fabricated by subsequent infiltration and curing procedure. Due to abundant oxygen groups associated with excellent dispersibility in aqueous solutions, graphene oxide (GO) is usually employed as popular building precursors to fabricate 3D GAs/GFs skeletons via a chemical reduction self-assembly process. However, these GAs/GFs often display a low electrical conductivity and an insufficient EMI SE level, which is mainly due to their high structural defects of GOs caused by the oxidative process. Although the electrical conductivity of GO-based CPCs can be partially enhanced through chemical or thermal reduction processes to yield rGO, there is still a gap toward practical applications. Thus, to further enhance the conductivity and EMI shielding properties, secondary conductive fillers, including 1D CNTs16, 19, magnetic particles (like Fe3O4 and Co3O4)20, 21, and metallic nanoparticles22, have been introduced into the GAs/GFs. Among these nanofillers, CNT has favorable mechanical and electrical properties, such as resistance to corrosion, light-weight, exceptional electrical conductivity (~106 S/cm), and remarkable mechanical properties (Young's modulus > 1 TPa), which can be used as an ideal secondary nanofiller. Despite these attractive merits, achieving a high-quality dispersion of the CNTs in an aqueous solution is still a key yet intractable issue due to its high aspect ratios and inherently strong hydrophobicity. Surface modification or introducing additional dispersants are usually adopted to enhance the dispersibility of pristine CNTs. For instance, Kim et al.16 fabricated a GF/CNT/PDMS composite that was prepared through a template-directed CVD



Page 4 of 26

method by applying acid-treated CNTs as the secondary conductive fillers. By using cellulose nanofiber (CNF) as the dispersant for multi-walled carbon nanotubes (MWCNTs), Fu et al.23 prepared a robust self-healing polyacrylamide (PAM)/MWCNTs/CNF hydrogel with an efficient EMI shielding performance. Apparently, surface acidizing treatment of CNTs can severely devastate their inherent surface structures along with their conductivity, and the extra addition of dispersant also increase the product cost. Herein, we demonstrate a more facile approach to prepare a flexible and highly conductive PDMS/rGO/SWCNTs composite for high-performance EMI shielding application. The composite was fabricated based on a two-step process using neat SWCNTs as the secondary conductive fillers for the first time, as illustrated in Figure 1a: (i) sol-gel self-assembly of reduced GO coupled with pristine SWCNTs and subsequent freeze-drying to create a robust 3D rGO/SWCNTs aerogel skeleton; (ii) infiltration of PDMS into the highly porous 3D network, followed by curing. Noteworthy, good dispersibility of GO enables pristine SWCNTs to evenly disperse in aqueous solution, avoiding the acidification treatment steps and completely preserve the high electrical conductivity of SWCNTs. The combination of GO and SWCNTs endowed the composite with a synergistically reinforced double conductive network. Consequently, the resultant composite exhibited a remarkable electrical conductivity of 1.20 S cm-1 and an excellent EMI SE of ~31 dB in the X-band frequency range at an ultralow rGO/SWCNTs loading of 0.28 wt%. Moreover, the mechanical properties and bending stability of the resultant PDMS composite were also investigated.

2. MATERIALS AND METHODS 2.1. Materials Natural graphite (purity > 99%, 300 mesh) was supplied from Qingdao Haida Co., Ltd. (China). Graphene oxides (GOs) were synthesized according to the modified Hummers method24, 25, which was specifically described in the Supporting Information (Figure S1 indicates that the thickness of GO nanosheets is ~1.1 nm). The concentrated sulphuric acid (H2SO4, 95%), nitric acid (HNO3, 60%),

hydrochloric

acid

(HCl,

37%),

potassium

permanganate

(KMnO4),

and

N,

N-dimethylformamide (DMF) were purchased from Laiyang fine chemical plant Co., Ltd. (China). Pristine SWCNTs synthesized by chemical vapour deposition method (purity > 95%, average external diameter ~2-4 nm, length ~30 µm, electrical conductivity > 100 S/cm) was purchased from Timesnano Co., Ltd. (China) and were thermally treated at 1300 °C under an inert


Page 5 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


atmosphere, then stored in DMF solution (1mg/mL) prior to use. L-ascorbic acid and hydrogen peroxide (H2O2, 30%) were supplied by Sinopharm Chemical Reagent Co., Ltd. (China). Polydimethylsiloxane (PDMS, RTV 615), consisting of the base agent A and curing agent B with the ratio of 10:1, was purchased from Momentive Performance Materials Co., Ltd. (USA). Ultrapure (UP) water (18.25 MΩ) was produced in the laboratory by ULUPURE (UPHeI-20T).

Figure 1. (a) Schematic illustration of the fabrication procedure of PTGCA composites; (b) Digital photograph of the ultralight TGCA3 aerogel with density of 2.5 mg cm−3 floating on a setaria viridis; (c) A test as a proof of the TGCA3 aerogel with excellent compressibility and superelasticity; (d-e) Optical images of PTGCA composites with diverse shapes (d) and the bent PTGCA3 with an outstanding flexibility (e).

2.2. Preparation of 3D rGO/SWCNTs Aerogels (GCAs, TGCAs) rGO/SWCNTs aerogels were fabricated through a sol-gel self-assembly method induced by a chemical reduction process. Typically, a certain amount of GO dispersion (3 mg/mL, 2 mL) and SWCNTs (6 mg) was added to a circular glass tube and mixed uniformly by homogenizing using a XHF-DY homogenizer at 4500 r/min for 20 min. After L-ascorbic acid was added as a chemical reducing agent (12 mg, L-ascorbic acid/GO = 2:1, w/w), the resulting aqueous dispersion was further mixed through magnetic stirring (15 min) and ultrasonication (10 min). Subsequently, the suspension was heated at 60 °C for 1 h to get partially reduced graphene oxide hydrogel, and then freezing the hydrogel at -18 °C for 10 h in a refrigerator followed by a thawing process. The obtained hydrogel was conducted a deep reduction at 60 °C for 10 h and dialyzed in UP water for 48 h to remove soluble species, followed by freeze-drying at -50 °C for 48 h to obtain a 3D



Page 6 of 26

rGO/SWCNTs aerogel (GCA). To further improve its conductivity, the GCA aerogel was thermally annealed at 800 °C for 1 h under nitrogen atmosphere with a heating rate of 10 °C/min, which was designated as TGCA. The aerogels with different weight ratios of SWCNTs to GO (GO content remained constant), i.e., 1:6, 1:5, 1:3, 1:1, were prepared in this work and the as-fabricated aerogels were named as TGCA1, TGCA2, TGCA3, TGCA4, respectively. Besides, rGO aerogel as a control was also prepared by a similar method. Densities of aerogels were calculated from the measured mass divided by the measured volume, as presented in Table 1. Table 1. Filler contents of PDMS composites and corresponding aerogel densities.

a

Samples

Weight ratios of SWCNTs/GO

Filler contents (wt%)

Aerogel densities (mg/cm3)

PDMSa SWCNTs/PDMS rGO/PDMS PTGCA1 PTGCA2 PTGCA3 PTGCA4

1:6 1:5 1:3 1:1

0 3.00 0.60 0.25 0.27 0.28 0.35

2.21 2.43 2.51 3.73

PDMS was prepared by direct curing at 60 °C for 4 h.

2.3. Preparation of PDMS/rGO/SWCNTs Composites (PTGCAs) PTGCAs were fabricated by backfilling PDMS into TGCAs with the aid of vacuum. The diluted PDMS solution was first prepared by dissolving 2 g PDMS (base A and curing agent B with the weight ratio of 10:1) into 10 mL n-hexane. Afterwards, TGCAs were immersed into the PDMS solution in a vacuum oven under ambient temperature for 60 min to completely remove bubbles and solvent, followed by curing of PDMS at 60 °C for 4 h. The composites prepared from different 3D TGCA aerogels (TGCAx, x=1, 2, 3, 4) were correspondingly designated as PTGCAx (x=1, 2, 3, 4). The total filler loadings of these composites can be calculated from the weights of fillers and corresponding PDMS composites, as summarized in Table 1. The composites can be prepared into different shapes such as rectangular solid and cylinder, as shown in Figure 1(d). For comparison, PGCAx with GCAs as skeletons, rGO/PDMS (filler content was 0.6 wt%) were also prepared by the similar backfilling procedure. Besides, SWCNTs/PDMS nanocomposites (filler content was 3.0 wt%) was also prepared by the solution blending method.

2.4. EMI Shielding Performance Measurements The microwave scattering parameters (S11 and S21) of the PTGCA composites (thickness ~2.0 ± 0.2


Page 7 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


mm) were measured on a vector network analyzer (PNA-X Network Analyzer N5244A, Figure S2) in the X-band frequency range of 8.2−12.4 GHz. S11 and S21 represent reflection coefficient data and transmission data, respectively. The total electromagnetic wave attenuated can be described by three major mechanisms using power coefficients, namely ： reflectivity (R), transmissivity (T), and absorptivity (A). The coefficients of (R), (T), and (A) can be evaluated from S11 and S21 according to the following equations26-28:

R = PR/P1 = |S11|2

(1)

T = PT/P1 = |S21|2

(2)

A = PA/P1 = (1 - R - T)/(1 - R)

(3)

Where P1 is the incident power, PT is the transmitted power, PR is the reflected power, and PA is the effectively absorbed power of the electromagnetic (EM) wave. The total EMI SE (SETotal) of a conductive polymer composite includes three contributions of reflection (SER), absorption (SEA) and multiple reflections (SEM). Note that the multiple reflections (SEM) can be ignored when SETotal > 15 dB6. Thus, the SETotal can be described by equation (4): SETotal = SER + SEA + SEM ≈ SER + SEA

(4)

Meanwhile, the reflective shielding effectiveness (SER), absorptive shielding effectiveness (SEA) can be calculated by Eqs (6) and (7)29, 30: SER= -10lg(1 - R)

(5)

SEA= -10lg(1 - A) = -10lg[T/(1 - R)]

(6)

2.5. Characterization The chemical compositions of GO, SWCNTs, GCA, and TGCA were evaluated by X-ray photoelectron spectroscopy (XPS, VG ESCALAB MARK II spectrometer). Thermogravimetric analysis (TGA) was recorded with a TA Instruments Q50 thermogravimetric analyzer under nitrogen atmosphere. X-ray diffraction (XRD) patterns were performed on a Bruker D8 X-ray diffractometer using Cu-Kα radiation (λ = 1.54 Å). A Renishaw in Via laser confocal Raman spectroscopy was used to characterize the structural evolution of TGCAs. Atomic force microscopy (AFM) measurement was performed in tapping mode on a Multimode 8 AFM



microscope. Ultraviolet-visible (UV-Vis) spectra measurement was carried out on a TU-1901PC spectrophotometer. The morphological features of 3D TGCAs network and PTGCA composites were observed with a scanning electron microscope (SEM, JEOL JSM-7500F). Electrical conductivities of the PTGCAs and PGCAs were determinated with a 4-probe PC68 high resistance meter. Compression stress-strain curves of neat PDMS and its nanocomposites were recorded using a universal material testing machine (Zwick/Roell Z020) outfitted with a 2.5 kN load at a compression rate of 2 mm/min.

3. RESULTS AND DISCUSSION 3.1 Dispersion of Pristine SWCNTs in Aqueous Solutions

Figure 2. (a) Digital photographs of GO/SWCNTs dispersions with different mass ratios of SWCNTs to GO, and right images are the bottom views of corresponding dispersions; (b) AFM image of GO/SWCNTs suspension (SWCNTs/GO = 1:3); (c) UV-vis spectra of GO and GO/SWCNTs aqueous dispersions. Good dispersibility of pristine SWCNTs in the aqueous solution is a crucial factor affecting the effectively construction of 3D rGO/SWCNTs aerogels and their PDMS composites. In this work, we ingeniously employ the assisting-dispersion effect of GO with excellent dispersing capability to facilitate an uniform distribution of SWCNTs in water phase. Particularly, the dispersion contents of pristine SWCNTs in a specific GO suspension (GO, 3 mg/mL, 2 mL) was explored. As presented in Figure 2a, when the mass ratios of SWCNTs to GO are lower than 1:3, SWCNTs can


Page 8 of 26

Page 9 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


be uniformly dispersed in GO solutions and yield a homogeneous and stable mixing suspension. With further increasing SWCNTs content (such as 1:1), however, the dispersion shows some flocculated precipitates at the bottom of the bottle, mainly derived from the agglomeration of excess SWCNTs as they exceed the saturated dispersibility of GO. Thus, the mass ratio of 1:3 obtains the optimal dispersion ratio of SWCNTs. To further identify the auxiliary dispersion mechanism of GO for SWCNTs, both AFM and UV-vis absorption spectra of GO/SWCNTs dispersions were observed. As evidenced in Figure 2b, SWCNTs present an individual distribution state and are closely attached onto the GO nanosheet surfaces, further demonstrating an efficient dispersion capacity of the GO for SWCNTs and implying high binding interactions between them. Moreover, Figure 2c indicates that there are two absorption peaks at 230 cm-1 (the transition of π-π*) and 305 cm-1 (the transition of n-π*) for GO suspension. By contrast, for GO/SWCNTs hybrids, the characteristic peaks of π-π* transition display a notable red shift. More specifically, the red shift extents of these peaks are approximately proportional to the SWCNTs/GO mass ratios when the ratios below 1:3. However, for GO/SWCNTs hybrid with the SWCNTs/GO mass ratio of 1:1, the red shift extent shows a reversely slight descent, which might attributed to the aggregation behavior of excess SWCNTs as indicated in Figure 2a. Such red shift phenomena of these π-π* transition peaks are believed to originate from the strong π-π interaction between GO and SWCNTs. Besides, hydrophobic interaction and Van der Waals force are another two pivotal binding forces between GO and SWCNTs on account of their hydrophobic properties and previously reported similar assembly mechanism between 2D GO and 1D nanofiber materials31, 32. As a result, pristine SWCNTs can be well dispersed into GO aqueous solutions via strong π-π, Van der Waals, and hydrophobic interactions, thereby avoiding undesired surface modification and completely maintaining its high electrical conductivity.

3.2 Fabrication of TGCAs and PTGCAs Based on the two-step strategy involving a chemical reduction-induced self-assembly of rGO/ SWCNTs and subsequent PDMS backfilling, TGCAs and PTGCAs had been successfully prepared. TGCA aerogel (2.5 mg cm−3) exhibits an ultralight performance that can steadily stand on a setaria viridis (Figure 1b, Video S1). TGCA aerogel also shows a superior compressibility and resilience, which can completely and rapidly recover to the initial state even at a high shrink



(Figure 1c, Video S2). Cyclic compression performances of our prepared aerogels (Figure S3) further clearly demonstrate their highly-efficient stability in compressibility and super-elasticity. Meanwhile, the PTGCA composites using highly flexible PDMS as the matrix exhibit an ideal flexibility, as seen from Figure 1e and Video S3, evidencing a promising application prospect in fields of aircraft, aerospace, and fast-growing flexible electronics/devices.

Figure 3. (a) XPS spectra, (b) TGA curves, and (c) Raman spectra of GO, SWCNTs, GCA3, and TGCA3. To monitor the chemical compositions and structural evolution of TGCAs during the fabrication process, XPS, TGA, and Raman spectra of the materials were systematically measured. Figure 3a presents the XPS spectra of GO, SWCNTs, GCA3, and TGCA3 aerogel. For SWCNTs, the O 1s peak was almost invisible and the C/O atomic ratio reached an extremely high value of 55.8. Compared with GO, GCA3 aerogel displayed a substantial decline in the O 1s peak intensity, suggesting the efficient removal of the vast majority of oxygen functional groups in GOs due to the chemical reduction by L-ascorbic acid during the hydrogel preparation course. More importantly, after subsequent thermal annealing (800 °C) for aerogels, the O 1s peak strength of TGCA3 was further dramatically reduced. The C/O atomic ratio of TGCA3 reached as high as 20.1 that was two times higher than that of GCA3 (9.8), which can be ascribed to a highly efficient reduction ability of the thermal annealing process. Detailed quantificational analysis toward XPS C1s deconvolution peaks of these materials has also been given in Figure S4, which further confirms the effective elimination of specific oxygenated groups in the materials. Meanwhile, Figure 3b shows the TGA curves of the materials. It was clearly observed that the weight losses of GO and SWCNTs during the whole measurement process were 35.63 and 0.91%, respectively. This results suggested that GO and SWCNTs possessed the highest and lowest content of oxygen-containing groups. Meanwhile, the weight losses of GCA3 (25.51%) and TGCA3 (9.35%) just fell in between those of GO and SWCNTs, which was mainly due to the


Page 10 of 26

Page 11 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


chemical reduction by L-ascorbic acid in hydrogel formation and subsequent thermal reduction processes. Obviously, the TGA results are in good consistent with the XPS results. Furthermore, Raman spectra of these materials were also performed and presented in Figure 3c. GO exhibits two typical characteristic peaks including D band at 1350 cm−1 and G band at 1590 cm−1 24. The G band represents graphitic carbons, while the D band is believed to originate from the structural defects and partially disordered graphitic domains33. The D band in GO spectrum was very strong and the intensity ratio of D to G bands (ID/IG) was as high as 1.06, proving a remarkable lattice distortions of graphene basal planes. An almost invisible D band of the SWCNTs confirms a nearly non-defective graphite lattice structure and thus allows it to remain the inherently excellent electrical conductivity. Moreover, as for GCA3 and TGCA3 obtained via the chemical reduction and further thermal reduction, the D-band intensities in Raman spectra substantially decreased. Consequently, the corresponding ID/IG values significantly declined from 1.06 (GO) to 0.47 (GCA3) and 0.23 (TGCA3), verifying the efficient restoration of a large number of structural defects34, 35. In addition, XRD patterns of the materials also further confirmed the structural change of TGCA composites during the preparation process (Figure S5). According to the above results, highly-efficient removal of oxygenated groups along with complete restoration of the structural defects in GO components have been successfully accomplished through both chemical and thermal reduction processes, paving the way towards an enhanced electrical conductivity and EMI shielding performance of the PDMS composites.

3.3 Morphology of 3D TGCAs and PTGCA Composites The microstructure morphologies of TGCAs were observed using SEM measurement. It is clearly seen that a highly porous and interconnected 3D architecture was formed in virtue of wellinterlinked graphene nanosheets, as shown in Figure 4a1. This 3D skeleton could be well preserved without any obvious deform/collapse after the high-temperature annealing, indicating a highly robust structure. As indicated in Figure 4(a2, a3), individual SWCNTs either be wrapped into the graphene layers or act as effective connecting bridges across adjacent graphene flakes. Therefore, combining the consecutively assembled 2D graphene flake channels with abundant 1D SWCNTs secondary pathways, a highly-efficient bicontinuous network formed in the 3D rGO/SWCNTs skeleton.



Figure 4. SEM images of highly porous 3D TGCA3 aerogel (a1, a2, a3) and the fracture surface of corresponding PTGCA3 composite (b1, b2, b3) at different magnifications. Figure 4b present the fracture-surface morphologies of PTGCA3 composite. It exhibits a neat fracture feature without visible micro-voids or pores inside the composite, indicating a validity of the backfilling method used in current work. It can be also found that continuous and porous 3D aerogel architectures were well retained after infiltrating with PDMS monomers (Figure 4b1), which is of great significance for the electrical conductivity, EMI SE, and mechanical properties of the PDMS composites. Additionally, slightly fuzzy and close-bonding interfaces between the aerogel network and PDMS matrix indicate a good interfacial compatibility (Figure 4b2), which would be benefit for an enhanced mechanical properties7. Meanwhile, as seen from Figure 4b3, the exposed parts of the SWCNTs showed a length of several micrometers, further signifying the high efficiency of SWCNTs as secondary network.

3.4 Electrical Conductivity of PTGCA Composites To identify the superiority of the preformed 3D rGO/SWCNTs double conductive network, the PTGCAs, SWCNTs/PDMS, and rGO/PDMS composites were compared in terms of conductivities. As seen in Figure 5, all the PTGCA composites reinforced with a 3D rGO/SWCNTs framework achieved a remarkable electrical conductivity of higher than 0.18 S cm−1 even at a lower filler loading (Table 1). Specifically, the conductivity of composites presented a trend of first rise and then fall as a function of the SWCNTs content, and the PTGCA3 achieves the highest value of 1.2 S cm−1 with only 0.28 wt% loading. Such phenomenon may be attributed to the dispersibility of


Page 12 of 26

Page 13 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


SWCNTs in aqueous solutions during the hydrogel preparation process as discussed above. It is a reasonable assumption that the dispersion states of SWCNTs in aqueous solutions, such as individual SWCNTs or closely bound SWCNT-bundles, can significantly affect their subsequent distribution in the 3D aerogel network and thus the electrical conductivity of composites. For comparison, the conductivities of PGCAs without thermal annealing were also measured (Figure S6), which are obviously lower than those of their heat-treated counterparts (PTGCAs). This result suggests that the effective repairing of structural defects on GO flakes in 3D rGO/SWCNTs aerogel by a high-temperature annealing is very beneficial to improve the electrical conductivity of materials.

Figure 5. The conductivities of pure PDMS, SWCNTs/PDMS, rGO/PDMS, and PTGCAs composites. Compared to PTGCA composites, the SWCNTs/PDMS composite displayed a low electrical conductivity of merely 2.1 × 10−10 S cm−1 with 3.0 wt % loading of isolated SWCNTs, which is 11 order of magnitude lower than that of our PTGCAs even with smaller filler loadings. Such distinct results can be explained by the dispersion state and connectivity of conductive fillers in polymer composites. Specifically, in SWCNTs/PDMS composite, it is difficult to form a continuous conducting network as most of the SWCNTs tend to accumulate together or are separated without interconnection, thus leading to an extremely low electrical conductivity. Interestingly, in our PTGCAs, the well-preserved interlinking 3D skeleton in the matrix can ensure the uniform distribution of carbon-based fillers and their efficient connection with each other, thereby yielding highly-efficient conducting channels for electron transport. Therefore, our preformed 3D



rGO/SWCNTs network offers a far superior conductivity as compared with that of conventional fillers/polymer blending composites. Moreover, the rGO/PDMS with 0.60 wt% loading of rGO exhibited a conductivity of 0.33 S cm−1, which is greatly lower than that of PTGCA3 (1.2 S cm−1) even with only 0.28 wt% of rGO and SWCNTs. Such result can be explained by the synergistic effect between GO and SWCNTs. It is generally believed that graphene nanosheets are inclined to reagglomerate in the reduction process for aerogel preparation because of the intermolecular π-π stacking attraction forces, thereby leading to an unfavorable effect for the electrical property. Besides, the pristine SWCNT used in this work significantly remain its excellent intrinsically electrical conductivity due to no acidification treatment. Therefore, thanks to its high aspect ratios and outstanding electrical conductivity, SWCNT can not only effectively restrain the reagglomeration of rGO nanosheets during the reduction process but also serve as secondary electrical channels among neighbouring graphene flakes36, resulting in a remarkable enhancement of conductivity. As a consequence, the rGO/SWCNTs bicontinuous conductive network endows PTGCAs with exceptional electrical conductivities at ultralow filler loadings, which are among the best values for similar conductive polymer nanocomposites (Table S1).

3.5 EMI Shielding Performances of PTGCA Composites Inspired by the excellent electrical conductivity, the EMI shielding performance of PTGCA composites was further measured in the X-band frequency range of 8.2−12.4 GHz (Figure 6). From Figure 6a, pure PDMS with an ultralow conductivity (6.2 × 10−12 S cm−1) exhibited a low SE value of less than 2 dB, implying that it was almost transparent to EM waves. In contrast, all the PTGCA composites exhibited remarkable EMI SE of higher than 27 dB over 8.2−12.4 GHz, far exceeding the target value of ~20 dB needed for the commercial application, and PTGCA3 with a conductivity of 1.2 S/cm acquired the highest EMI SE of around 31 dB. Obviously, with increasing SWCNTs content, the EMI SE values presented a similar change tendency as that of the electrical conductivity of the same composites, indicating that the EMI SE is largely influenced by the electrical properties of composites. SE values of PGCA composites with relatively lower conductivities were both smaller than those of corresponding PTGCA composites (Figure 6b), further confirming the crucial role of conductivity for their shielding performances. Additionally,


Page 14 of 26

Page 15 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


SE results of pure TGCA aerogels presented in Figure S7 demonstrate that 3D conductive aerogels play a decisive role on the EMI SE performance of PTGCA nanocomposites.

Figure 6. (a, b) Plots of EMI SE versus frequency for neat PDMS and PTGCA composites filled with different TGCA aerogels (a) and PGCA composites filled with different GCA aerogels (b); (c) Comparison of SETotal, SEA, and SER of PTGCA composites at a frequency of 12.4 GHz; (d) Schematic illustrating the EMI shielding mechanisms of PTGCA composites; (e, f) Dielectric loss tangent (tan δε = ε″/ε′) of PTGCAs (e) and PGCAs (f). It is noteworthy that the filler loadings of rGO/SWCNTs in the PTGCA composites (ranging from 0.25 to 0.35 wt%) were much lower than those of carbon-based composites with similar SE values prepared by conventional blending methods. To better compare the EMI shielding performance among different polymer composites, we proposed a concept of the specific SE value (SETotal divided by the corresponding weights of filler loadings, dB/unit wt%) by considering the contribution efficiency of per unit filler loading. Table S1 compares the EMI shielding performance of our PTGCAs with those of recently reported carbon filler/polymer nanocomposites. Clearly, for carbon/polymer blending composites, high loadings of carbon fillers, such as 10-15 wt% graphene or CNTs12, 37, 38, are required to achieve rather moderate SE values of 20-27 dB over X-band frequency range. These commonly blending composites also showed lower specific SE values of less than 6.4 dB/unit wt%. In comparison, backfilling strategy provides an extremely high-efficient approach to accomplish excellent shielding performance with lower filler loadings. For example, a SE of ~27 dB was achieved for PDMS/graphene foam composites with a 0.8 wt% graphene loading9, and an epoxy/CNT sponge nanocomposite displayed a SE value of 33 dB using



0.66 wt% CNT sponge7. Meanwhile, the specific SE values of these composites were much higher than those of carbon/polymer blending composites. More importantly, our PTGCA nanocomposites presented a superior SE value of 31 dB at an extremely low loading of 0.28 wt%, which is among the best shielding performances at low filler loadings7-9, 13, and showed the highest specific SE values of around 110 dB/unit wt% among all the reported polymer composites so far, suggesting its great potential as a high performance EMI-shielding material. To further illuminate the shielding mechanisms of PDMS nanocomposites, the SETotal and the contribution from absorption (SEA) and reflection (SER) as a function of electrical conductivity at 12.4 GHz were compared, as indicated in Figure 6c. It can be clearly observed that, with increasing electrical conductivity, both the SETotal and SEA increased while SER remained almost unchanged. Meanwhile, the contribution of absorption (SEA) to the EMI SE is much larger than that of reflection (SER), e.g., the values of SEA and SER for PTGCA3 were 30.8 dB, 1.1 dB, respectively, demonstrating an absorption-dominant shielding mechanism for these PTGCA composites. Such result may be attributed to their highly porous structure along with the interior 3D interconnected conductive framework39. Figure 6d visually illustrated the EMI shielding process of composites. Specifically, on one hand, highly porous structure could effectively decrease the impedance mismatch between the PDMS composites and air interfaces, thus greatly weakening the surface reflection and enabling most EM waves deep penetration into the composites. On the other hand, the higher conductivity of 3D rGO/SWCNTs network combined with numerous matrix-2D laminar rGO interfaces make the incoming EM waves substantial attenuation by repeatedly conductive dissipation (absorption) and multiple reflections and scattering. Hence, the vast majority of incident microwaves have been absorbed and dissipated so that only an extremely tiny part could traverse the composites, yielding a highly-efficient EMI shielding performance. In addition, the complex permittivity (εr = ε′ - iε″) of the composites had also been measured to better understand their EM absorption performances, as given in Figure 6 (e, f). It is well known that the real part (ε′) and imaginary part (ε″) of complex permittivity (εr) represent the storage capability and loss capability of the electric energy, respectively,1, 40 and the dielectric loss tangent (tan δε = ε″/ε′) is often used as the characteristic parameter to evaluate the dielectric loss capacity of materials. Apparently, the dielectric loss tangent values of PTGCAs and PGCAs are


Page 16 of 26

Page 17 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


proportional to their electrical conductivities (Figure 5 and Figure S6). Meanwhile, PTGCAs exhibited much higher dielectric loss tangent values, of which PTGCA3 achieved the highest value of as high as 0.6-0.78. These results imply that PTGCA composites possess superior dielectric loss capacity, which thus can significantly make electrical energy dissipate and microwaves absorption attenuate. Such high dielectric loss is believed to result from the combined effect of conductivity loss and interfacial polarization loss. As mentioned above, the interconnected 3D rGO/SWCNTs double conductive network was perfectly inherited by composites, thereby providing sufficiently fast electron pathways and causing the prominent conductivity loss. Besides, the interfacial polarization also appeared in our PTGCAs deriving from the abundant interfaces between PDMS matrix and fillers, which was caused by the fact that these neighboring two phases own distinct properties regarding dielectric constant or conductivity. Note that no visible resonance peaks are observed in the dielectric loss tangent curve, hence, the conductivity loss results in the major contribution to the dielectric loss of the composites41. Overall, on the basis of the above discussion, this remarkable absorption-dominant shielding feature renders PTGCA composites promising and alluring advantages over those reflection-dominant EM shielding materials, which can be used in various fields including electronic circuits, specific aircraft, military stealth coating, etc.

3.6 Mechanical Performances and Flexibility of PTGCA Composites Apart from high EMI shielding performance, excellent mechanical properties and stability are also highly needed for shielding materials toward effective and practical EMI shielding applications. Figure 7a presents the compression properties of neat PDMS and its nanocomposites. It can be seen that the PTGCA nanocomposites exhibited remarkable increases in both compression strength and modulus in comparison with the neat PDMS. The compression properties reinforcement of these PTGCA composites is roughly proportional to the filler loadings. Particularly, for PTGCA3 exhibiting the optimal electrical and EMI shielding properties, the incorporation of only 0.28 wt% rGO/SWCNTs improved both the compression strength and modulus by 233% and 108%, respectively, in comparison to pure PDMS. Such excellent mechanical properties of PTGCA composites reinforced with rGO and SWCNTs may be originated from the following critical factors. On one hand, the good interfacial compatibility between 3D fillers skeleton and PDMS matrix evidenced by the SEM results (Figure 4b) is believed to facilitate the enhancement in mechanical properties for PTGCA composites. On the other hand, the preformed robust 3D



rGO/SWCNTs network throughout the whole matrix can be served as the highly-efficient interlinked pathways for the external stress transfer, thereby greatly improving the mechanical properties of the PTGCA composites. Additionally, longer (several micrometers) and evenly dispersed SWCNTs inside the PDMS matrix provide effective reinforcement to the mechanical properties of composites due to their notably reinforcing effect, as previously reported7, 42.

Figure 7. (a) Compression stress-strain curves of neat PDMS and its nanocomposites; (b) The resistance change of the PTGCA composites under repeatedly bending process (bend radius < 2.0 mm, 10 000 times). The upper inset is the resistance testing apparatus. The bottom inset shows a schematic for the bending process of the composite. To explore the stability of PTGCA nanocomposites under continuous mechanical deformation, we examined the electrical conductivity of the PTGCA composite before and after repeated bending. Figure 7b demonstrates that the electrical conductivity of the PDMS composite remains almost constant less than 1000 times repetitive bending. Further increasing the bending cycle until to 10 000 times, the conductivity only exhibited very small decline, which may result from the partial structural failure of the rGO/SWCNTs framework. Consequently, such remarkable mechanical robustness and flexibility enable potential application of the PTGCA composites as highly efficient EMI shielding materials in fast growing next-generation flexible electronics, such as portable electronics and wearable devices.

4. CONCLUSIONS In summary, we have successfully fabricated flexible PTGCA nanocomposites with excellent EMI SE and mechanical properties by a facile backfilling strategy, that is, impregnating PDMS into a porous and interconnected 3D rGO/SWCNTs aerogel network. The preformed 3D rGO/SWCNTs aerogel was prepared via a sol-gel self-assembly process, which ingeniously achieved the uniform


Page 18 of 26

Page 19 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


dispersion of GO and pristine SWCNTs in the matrix. Fortunately, the 3D bicontinuous carbon network serves as highly-efficient pathways for electron transport, enabling a remarkable electrical conductivity of 1.2 S/cm and thus an outstanding EMI SE of 31 dB in the X-band frequency range for the resulting composites with only 0.28 wt% rGO and SWCNTs. Moreover, the PTGCA composites reinforced with the robust 3D skeleton exhibited an excellent mechanical properties, 233% and 108% enhancements were achieved for compression strength and modulus, respectively, compared to the neat PDMS. The excellent flexibility also enables this nanocomposite a stable EMI shielding performance under repeated bending deformation process. Therefore, owing to the characteristics of easy processing, remarkable electrical conductivity and shielding performance at ultralow filler loading, as well as outstanding mechanical robustness and flexibility, this novel nanocomposite shows a great potential for high-performance EMI shielding application.

ASSOCIATED CONTENT Supporting Information Synthesis of graphene oxides (GOs); Experiment apparatus of EMI shielding measurement; Cyclic compression performance of TGCAs and PTGCAs; XPS C1S core level spectra analysis; XRD analysis of the materials; Electrical conductivities of PGCAs; EMI SE performance of TGCA aerogels; Comparisons of EMI shielding performance of different carbon-based fillers/polymer nanocomposites; Video S1, showing the lightweight property of TGCA3 aerogel (AVI); Video S2, showing the compressibility and super-elasticity of TGCA3 aerogel (AVI); Video S3, showing the flexibility of PTGCA3 composite (AVI).

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (G. Zhang). ORCID Guangfa Zhang: 0000-0002-8632-1264 Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS The authors would like to gratefully acknowledge the National Natural Science Foundation of China (No. 51703113 and 51703111), Shandong Provincial Natural Science Foundation (No.



ZR2017BEM039, ZR2017BEM011, and ZR2016XJ001), and China Postdoctoral Science Foundation (2018M630763) for supporting this work.

ABBREVIATIONS GCA, 3D rGO/SWCNTs aerogel; TGCA, 3D rGO/SWCNTs aerogel after thermal annealing treatment; PTGCA, PDMS/rGO/SWCNTs composite.

REFERENCES (1) Liu, C.; Wang, X.; Huang, X.; Liao, X.; Shi, B. Absorption and Reflection Contributions to the High Performance of Electromagnetic Waves Shielding Materials Fabricated by Compositing Leather Matrix with Metal Nanoparticles. ACS Appl. Mater. Inter. 2018, 10, 14036-14044. (2) Liu, J.; Zhang, H.; Sun, R.; Liu, Y.; Liu, Z.; Zhou, A.; Yu, Z. Hydrophobic, Flexible, and Lightweight MXene Foams for High-Performance Electromagnetic-Interference Shielding. Adv. Mater. 2017, 29, 1702367. (3) Song, W.; Gong, C.; Li, H.; Cheng, X.; Chen, M.; Yuan, X.; Chen, H.; Yang, Y.; Fang, D. Graphene-Based Sandwich Structures for Frequency Selectable Electromagnetic Shielding. ACS Appl. Mater. Inter. 2017, 9, 36119-36129. (4) Zeng, Z.; Chen, M.; Pei, Y.; Seyed Shahabadi, S. I.; Che, B.; Wang, P.; Lu, X. Ultralight and Flexible Polyurethane/Silver Nanowire Nanocomposites with Unidirectional Pores for Highly Effective Electromagnetic Shielding. ACS Appl. Mater. Inter. 2017, 9, 32211-32219. (5) Li, Y.; Shen, B.; Pei, X.; Zhang, Y.; Yi, D.; Zhai, W.; Zhang, L.; Wei, X.; Zheng, W. Ultrathin Carbon Foams for Effective Electromagnetic Interference Shielding. Carbon 2016, 100, 375-385. (6) Li, X. H.; Li, X.; Liao, K. N.; Min, P.; Liu, T.; Dasari, A.; Yu, Z. Z. Thermally Annealed Anisotropic Graphene Aerogels and Their Electrically Conductive Epoxy Composites with Excellent Electromagnetic Interference Shielding Efficiencies. ACS Appl. Mater. Inter. 2016, 8, 33230-33239. (7) Chen, Y.; Zhang, H.; Yang, Y.; Wang, M.; Cao, A.; Yu, Z. High-Performance Epoxy


Page 20 of 26

Page 21 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Nanocomposites Reinforced with Three-Dimensional Carbon Nanotube Sponge for Electromagnetic Interference Shielding. Adv. Funct. Mater. 2016, 26, 447-455. (8) Jia, J.; Sun, X.; Lin, X.; Shen, X.; Mai, Y.; Kim, J. Exceptional Electrical Conductivity and Fracture Resistance of 3D Interconnected Graphene Foam/Epoxy Composites. ACS Nano 2014, 8, 5774-5783. (9) Chen, Z.; Xu, C.; Ma, C.; Ren, W.; Cheng, H. Lightweight and Flexible Graphene Foam Composites for High-Performance Electromagnetic Interference Shielding. Adv. Mater. 2013, 25, 1296-1300. (10) Yousefi, N.; Sun, X.; Lin, X.; Shen, X.; Jia, J.; Zhang, B.; Tang, B.; Chan, M.; Kim, J. Highly Aligned

Graphene/Polymer

Nanocomposites

with

Excellent

Dielectric

Properties

for

High-Performance Electromagnetic Interference Shielding. Adv. Mater. 2014, 26, 5480-5487. (11) Zhang, H.; Yan, Q.; Zheng, W.; He, Z.; Yu, Z. Tough Graphene-Polymer Microcellular Foams for Electromagnetic Interference Shielding. ACS Appl. Mater. Inter. 2011, 3, 918-924. (12) Liang, J.; Wang, Y.; Huang, Y.; Ma, Y.; Liu, Z.; Cai, J.; Zhang, C.; Gao, H.; Chen, Y. Electromagnetic Interference Shielding of Graphene/Epoxy Composites. Carbon 2009, 47, 922-925. (13) Chen, Y.; Zhang, H. B.; Wang, M.; Qian, X.; Dasari, A. Phenolic Resin-Enhanced Three-Dimensional Graphene Aerogels and Their Epoxy Nanocomposites with High Mechanical and Electromagnetic Interference Shielding Performances. Compos. Sci. Technol. 2017, 152, 254-262. (14) Choi, W.; Choi, K.; Yu, C. Ultrafast Nanoscale Polymer Coating on Porous 3D Structures Using Microwave Irradiation. Adv. Funct. Mater. 2017, 1704877. (15) Wu, Y.; Wang, Z.; Liu, X.; Shen, X.; Zheng, Q.; Xue, Q.; Kim, J. Ultralight Graphene Foam/Conductive Polymer Composites for Exceptional Electromagnetic Interference Shielding. ACS



Appl. Mater. Inter. 2017, 9, 9059-9069. (16) Sun, X.; Liu, X.; Shen, X.; Wu, Y.; Wang, Z.; Kim, J. Graphene Foam/Carbon Nanotube/Poly(dimethyl siloxane) Composites for Exceptional Microwave Shielding. Compos. Part A-Appl. S. 2017, 92, 190-197. (17) Chen, Z.; Ren, W.; Gao, L.; Liu, B.; Pei, S.; Cheng, H. M. Three-Dimensional Flexible and Conductive Interconnected Graphene Networks Grown by Chemical Vapour Deposition. Nat. Mater. 2011, 10, 424. (18) Chen, M.; Tao, T.; Zhang, L.; Gao, W.; Li, C. Highly Conductive and Stretchable Polymer Composites Based on Graphene/MWCNT Network. Chem. Commun. 2013, 49, 1612-1614. (19) Singh, A. P.; Mishra, M.; Hashim, D. P.; Narayanan, T. N.; Hahm, M. G.; Kumar, P.; Dwivedi, J.; Kedawat, G.; Gupta, A.; Singh, B. P.; Chandra, A.; Vajtai, R.; Dhawan, S. K.; Ajayan, P. M.; Gupta, B. K. Probing the Engineered Sandwich Network of Vertically Aligned Carbon Nanotube-Reduced Graphene Oxide Composites for High Performance Electromagnetic Interference Shielding Applications. Carbon 2015, 85, 79-88. (20) Chen, Y.; Wang, Y.; Zhang, H.; Li, X.; Gui, C.; Yu, Z. Enhanced Electromagnetic Interference Shielding Efficiency of Polystyrene/Graphene Composites with Magnetic Fe3O4 Nanoparticles. Carbon 2015, 82, 67-76. (21) Liu, P.; Huang, Y.; Sun, X. Excellent Electromagnetic Absorption Properties of Poly(3,4-ethylenedioxythiophene)-Reduced Graphene Oxide-Co3O4 Composites Prepared by a Hydrothermal Method. ACS Appl. Mater. Inter. 2013, 5, 12355-12360. (22) Kumar, R.; Kumari, S.; Dhakate, S. R. Nickel Nanoparticles Embedded in Carbon Foam for Improving Electromagnetic Shielding Effectiveness. Appl. Nanosci. 2015, 5, 553-561.


Page 22 of 26

Page 23 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(23) Yang, W.; Shao, B.; Liu, T.; Zhang, Y.; Huang, R.; Chen, F.; Fu, Q. Robust and Mechanically and Electrically Self-Healing Hydrogel for Efficient Electromagnetic Interference Shielding. ACS Appl. Mater. Inter. 2018, 10, 8245-8257. (24) Chen, J.; Yao, B.; Li, C.; Shi, G. An Improved Hummers Method for Eco-Friendly Synthesis of Graphene Oxide. Carbon 2013, 64, 225-229. (25) Jiang, Z.; Yang, W.; He, F.; Xie, C.; Fan, J.; Wu, J.; Zhang, K. Modified Phase Change Microcapsules with Calcium Carbonate and Graphene Oxide Shells for Enhanced Energy Storage and Leakage Prevention. ACS Sustain. Chem. Eng. 2018, 6, 5182-5191. (26) Shen, B.; Li, Y.; Yi, D.; Zhai, W.; Wei, X.; Zheng, W. Microcellular Graphene Foam for Improved Broadband Electromagnetic Interference Shielding. Carbon 2016, 102, 154-160. (27) Zhao, B.; Zhao, C.; Li, R.; Hamidinejad, S. M.; Park, C. B. Flexible, Ultrathin, and High-Efficiency Electromagnetic Shielding Properties of Poly(Vinylidene Fluoride)/Carbon Composite Films. ACS Appl. Mater. Inter. 2017, 9, 20873-20884. (28) Zhu, C.; Guo, S.; Fang, Y.; Dong, S. Reducing Sugar: New Functional Molecules for the Green Synthesis of Graphene Nanosheets. ACS Nano 2010, 4, 2429-2437. (29) Cao, M.; Wang, X.; Cao, W.; Yuan, J. Ultrathin Graphene: Electrical Properties and Highly Efficient Electromagnetic Interference Shielding. J. Mater. Chem. C 2015, 3, 6589-6599. (30) Song, W. L.; Wang, J.; Fan, L. Z.; Li, Y.; Wang, C. Y.; Cao, M. S. Interfacial Engineering of Carbon

Nanofiber-Graphene-Carbon

Nanofiber

Heterojunctions

in

Flexible

Lightweight

Electromagnetic Shielding Networks. ACS Appl. Mater. Inter. 2014, 6, 10516-10523. (31) Xiong, R.; Hu, K.; Grant, A. M.; Ma, R.; Xu, W.; Lu, C.; Zhang, X.; Tsukruk, V. V. Ultrarobust Transparent Cellulose Nanocrystal-Graphene Membranes with High Electrical Conductivity. Adv.



Page 24 of 26

Mater. 2016, 28, 1501-1509. (32) Xiong, R.; Kim, H. S.; Zhang, L.; Korolovych, V. F.; Zhang, S.; Yingling, Y. G.; Tsukruk, V. V. Wrapping Nanocellulose Nets around Graphene Oxide Sheets. Angew. Chem. Int. Edit. 2018, DOI: 10.1002/anie.201803076. (33) Zhao, S.; Xie, S.; Zhao, Z.; Zhang, J.; Li, L.; Xin, Z. Green and High-Efficiency Production of Graphene by Tannic Acid-Assisted Exfoliation of Graphite in Water. ACS Sustain. Chem. Eng. 2018, DOI: 10.1021/acssuschemeng.8b00497. (34) Xin, G.; Sun, H.; Scott, S. M.; Yao, T.; Lu, F.; Shao, D.; Hu, T.; Wang, G.; Ran, G.; Lian, J. Advanced Phase Change Composite by Thermally Annealed Defect-Free Graphene for Thermal Energy Storage. ACS Appl. Mater. Inter. 2014, 6, 15262-15271. (35) Worsley, M. A.; Pham, T. T.; Yan, A.; Shin, S. J.; Lee, J. R. I.; Bagge-Hansen, M.; Mickelson, W.; Zettl, A. Synthesis and Characterization of Highly Crystalline Graphene Aerogels. ACS Nano 2014, 8, 11013-11022. (36) Wang, Y.; Wu, Y.; Huang, Y.; Zhang, F.; Yang, X.; Ma, Y.; Chen, Y. Preventing Graphene Sheets from Restacking for High-Capacitance Performance. J. Phys. Chem. C 2011, 115, 23192-23197. (37) Ling, J.; Zhai, W.; Feng, W.; Shen, B.; Zhang, J.; Zheng, W. G. Facile Preparation of Lightweight

Microcellular

Polyetherimide/Graphene

Composite

Foams

for

Electromagnetic

Interference Shielding. ACS Appl. Mater. Inter. 2013, 5, 2677-2684. (38) Abbas, N.; Kim, H. T. Multi-Walled Carbon Nanotube/Polyethersulfone Nanocomposites for Enhanced Electrical Conductivity, Dielectric Properties and Efficient Electromagnetic Interference Shielding at Low Thickness. Macromol. Res. 2016, 24, 1084-1090. (39) Shen, B.; Li, Y.; Zhai, W.; Zheng, W. Compressible Graphene-Coated Polymer Foams with


Page 25 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Ultralow Density for Adjustable Electromagnetic Interference (EMI) Shielding. ACS Appl. Mater. Inter. 2016, 8, 8050-8057. (40) Ashwani, K. S. A. A. Lightweight Reduced Graphene Oxide-Fe3O4 Nanoparticle Composite in the Quest for an Excellent Electromagnetic Interference Shielding Material. Nanotechnology 2018, 29, 245203. (41) Wu, F.; Xie, A.; Sun, M.; Wang, Y.; Wang, M. Reduced Graphene Oxide (RGO) Modified Spongelike Polypyrrole (PPy) Aerogel for Excellent Electromagnetic Absorption. J. Mater. Chem. A 2015, 3, 14358-14369. (42) Yan, D.; Pang, H.; Li, B.; Vajtai, R.; Xu, L.; Ren, P.; Wang, J.; Li, Z. Structured Reduced Graphene Oxide/Polymer Composites for Ultra-Efficient Electromagnetic Interference Shielding. Adv. Funct. Mater. 2015, 25, 559-566.



Graphical abstract


Page 26 of 26

Flexible PDMS Nanocomposites Enhanced with Three-dimensional

Recommend Documents