Quick Heat Dissipation in Absorption-Dominated Microwave Shielding

Subscriber access provided by UNIV OF LOUISIANA

Functional Nanostructured Materials (including low-D carbon)

Quick Heat Dissipation in Absorption-Dominated Microwave Shielding Properties of Flexible PVDF/CNT/Co Composite Films with Anisotropy-Shaped Co (Flowers or Chains) Xiping Li, Shuiping Zeng, Shiju E, Luyang Liang, Zhongyi Bai, Yuanyuan Zhou, Biao Zhao, and Rui Zhang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b14733 • Publication Date (Web): 01 Nov 2018 Downloaded from http://pubs.acs.org on November 1, 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 34 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

Quick Heat Dissipation in Absorption-Dominated Microwave Shielding Properties of Flexible PVDF/CNT/Co Composite Films with Anisotropy-Shaped Co (Flowers or Chains) Xiping Li †, Shuiping Zeng †, Shiju E†, Luyang Liang ‡, Zhongyi Bai ‡, Yuanyuan Zhou ‡, Biao Zhao ‡, §, *, Rui Zhang ‡, ∥ † College ‡

of Engineering, Zhejiang Normal University, Jinhua, 321004, PR China

Henan Key Laboratory of Aeronautical Materials and Application Technology, School of

Material Science and Engineering, Zhengzhou University of Aeronautics, Zhengzhou, Henan 450046, China §

Department of Mechanical and Industrial Engineering, University of Toronto, 5 King’s College

Road, Toronto, Ontario M5S 3G8, Canada ∥

School of Material Science and Engineering, Zhengzhou University, Zhengzhou, Henan

450001, China *Corresponding

Author:

Dr. Biao Zhao E-mail address: [email protected] Tel: +86-371-60632007 Fax: +86-371-60632600 Abstract: The facile fabrication of thin flexible electromagnetic interference (EMI) shielding materials with fast heat dissipation for adaptable tuning in both civil and military applications is in urgent demand. In our work, the flexible poly(vinylidene fluoride) (PVDF)/carbon nanotubes (CNT) composite films decorated with anisotropy-shaped Co in flowers or chains were prepared 1 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

Page 2 of 34

and studied. The results showed that, by increasing the Co filler contents, the EC (electrical conductivity), TC (thermal conductivity) and EMI (electromagnetic interference) shielding properties of such PVDF/CNT/Co (flowers or chains) flexible films were significantly improved. In contrast, the PVDF/CNT/Co-chains flexible films exhibit higher performance with respect to the EC, TC and EMI shielding property. A total shielding of 35.3 dB and 32.2 dB were respectively obtained by the PVDF/CNT/6 wt%Co-chain with an EC of 2.28 S/cm and the PVDF/CNT/ 6wt% Co-flower with an EC of 1.94 S/cm at a film thickness of 0.3 mm. Possibly owning to the conductive dissipation, interfacial polarization, magnetic loss, multiple reflections and scattering of EM waves, such flexible composite films possessed a remarkable absorptiondominated EMI shielding behavior. These new composite films with enhanced TC are easily able to transform microwave energy into Joule heating systems, making themselves greatly potential for effective EMI shielding as well as rapid heat dissipation. Keywords: flexible PVDF/CNT/Co films, EMI shielding, absorption-dominated mechanism, conduction loss, magnetic loss, heat dissipation 1. Introduction Last decades, the flourishing development of advanced information technology, especially the electronic devices and other telecommunication facilities, makes our daily life convenient. However, wide usage of electronic devices inevitably cause serious electromagnetic interference (EMI) radiation problem, which not only deteriorates the performance of precision devices nearby but also threatens the health of human beings.

1-7

Consequently, the quest for high-

efficiency materials towards EMI pollution suppression has become an applausive research topic. 8-13

Metallic shields, despite being widely used as a common means for conventional EMI

2 ACS Paragon Plus Environment


Page 3 of 34 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

shielding materials containing metal foil, metal mesh, and conductive coating, suffer from several disadvantages such as high density, cumbersome processing,14-15 large thickness, susceptibility to corrosion, and lack of transparency. Such practical concerns largely put a brake on further development of particular cases, for instance, the aerospace, automobiles and nextgeneration microelectronics, etc. To solve this problem, scientists have been seeking the help from polymer composites, which offer myriad advantages like low density, high resistance to corrosion, ease of processing, and so on. 9, 16-18 As an alternative way to obtain high shielding effectiveness (SE), conductive polymer composites consisting of carbon-based materials, for instance, carbon fibers, carbon nanotubes (CNT) and graphene, have gained acclaim owning to their tunable aspect ratio, light weight, high EC, and flexibility. 19-35 From the theoretical view of EMI shielding, it is generally believed that that the principle for shielding EM waves is mainly attributed to three key mechanisms, including reflection, absorption, and multiple reflections. However, it should be noted that the SE value of conductive polymer composites is closely related with the reflection mechanism, which may also induce secondary EMI pollution. Thus, materials having charge carriers or magnetic/electric dipoles should be focused on for developing EMI shielding materials with strong absorption property. In contrast to conducting carbons (CNT), ferromagnetic-doped carbonaceous derivatives are often included in the polymeric matrix for triggering tremendous magnetic loss. Mural et al.

36

prepared sea-island-type morphology in f polyethylene (PE)/poly(ethylene oxide) (PEO) (70/30 w/w) blend, which is able to attenuate EM radiation when by incorporating 3 wt% of MWCNT and 10 vol% of rGO–Ni. The addition of rGO along with the conducting MWCNT strikingly enhanced the overall conductivity of the blend. The higher conductivity and higher magnetic



Page 4 of 34

permeability efficiently enhanced the absorption-dominated shielding efficiency, with 26 dB total shielding effectiveness. Menon et al.

37

reported the FeNi alloy particles were coated with

MWCNT using simple ball milling technique at different ratios of alloy/MWNT. These hybrids were then dispersed in PVDF/TPU (thermoplastic polyurethane) blends for the formation of flexible composite materials. It was indicated that these MWCNT wrapped magnetic alloy particles appear to attenuate the incoming EM radiations more effectively in comparison with cases of only MWNTs or alloy particles. Biswas et al.

38

fabricated a multilayered assembly

containing “flower-like” Fe3O4 nanoparticles conjugated on the defect sites of surface functionalized MWCNT by using polymeric PVDF and polycarbonate (PC) blends. This unique absorption-dominated shielding resulted in a high SE of 64 dB at a frequently of 18.0 GHz thanks to the interfacial polarization of different heterogeneous structures. Lee et al. 39 provided a simple and rapid route to synthesize multi-layered and interconnected 3D graphene-CNT-Fe2O3 heterostructures for enhanced flexibility and wideband EMI shielding capability. Based on above-mentioned discussion, it is concluded that combining magnetic materials and CNT would necessarily enhance the EC and EMI shielding performance for polymer composites. However, to our knowledge, few publications are addressed with the effects of anisotropy-shaped magnetic particles on the EMI shielding properties of polymer composites. Herein, we intend to investigate the influences of ferromagnetic anisotropy-shaped Co (flowers or chains) on the EC and EMI shielding performance of flexible PVDF/CNT/Co films. For absorption-dominated microwave shielding materials, absorbing microwave energy with the capability of fast heat dissipation is critically preferable, since long-term exposure to microwave would have a negative impact on the lifetime of EMI shielding devices. Therefore, it is necessary to integrate an efficient thermal control system for further miniaturization of all sorts of


Page 5 of 34 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 interfaces.40 Unfortunately, the TC of EMI shielding materials is taken less attention thus far.41-42 In this work, we used infrared camera to observe the temperature variation of PVDF/CNT/Co (flower or chain) flexible films under microwave irradiation, and their TCs were also measured to evaluate the heat dissipation of flexible composite films. In a word, the Co anisotropy shape affects the EC and EMI shielding property of composite films, and these flexible PVDF/CNT/Co (flower or chain) films exhibit high-efficiency EMI shielding performances along with quick heat dissipation features. 2. Experimentation2.1. Raw Materials The MWCNT (NC7000™) were provided by Nanocyl SA. Hexamethylene tetramine (C6H2N4) were purchased from Luoyang Chemical Reagent Factory (Henan, China). 1,2-propanediol (C3H8O2) was purchased from Tianjin Kemiou Chemical Reagent Co., Ltd. (Tianjin, China). Cobalt (II) chloride hexahydrate (CoCl2·6H2O) and sodium hydrate (NaOH) were obtained from Tianjin Fengchuan Chemical Reagent Technologies Co., Ltd. (Tianjin, China). Hydrazine hydrate (N2H4·H2O) was provided From Tianjin Fuyu Fine Chemical Co., Ltd. (Tianjin, China). N,N-Dimethylformamide (DMF) was purchased from Sigma-Aldrich. All reagents were of analytical grade and used without any further purification. The PVDF was supplied by Solvay. 2.2 Preparation of Anisotropy-Shaped Co (Flowers and Chains) Co Chains: The preparation process is similar with Yu’s work that the one-dimension NiCo chains in the presence of magnetic field were prepraed.

43

In a typical preparation method, 60 ml of 1,2-

propanediol and 1.2 mmol of CoCl2·6H2O were first added to a beaker, and stirred for 30 minutes. Afterwards, 1.8 mmol of hexamethylenetetramine was added and mixed with magnetic stirring for 15 minutes at 120 °C. Finally, 6 mmol NaOH was added and mixed uniformly with 5 ACS Paragon Plus Environment


Page 6 of 34

mechanical stirring for 10 minutes. The mixture was then transferred to a Teflon reaction vessel and placed in a heating furnace under a magnetic flux density of 0.15 T and heated to 170 °C for 20 hours. Following the completion of reaction, the final products were obtained after being washed using distilled water and ethanol, and then dried at 50 °C under vacuum for 12 h. Co Flowers: The Co flowers were prepared according to the previous modified method.44 In a typical procedure, CoCl2.6H2O (225 mM) and NaOH (1 M) were dissolved in distilled water with a volume of 50 ml. About 16mL hydrazine hydrate (N2H4·H2O) used as a reducing agent, was added to the solution.. The mixed solution was stirred drastically and then placed to a Teflon reaction vessel. The mixture was reacted at 120 °C for 4 hours and thereafter cooled to the ambient temperature. Distilled water and ethanol were utilized to remove the residual alkaline salt. By using a magnet, the final product was obtained after being dried under vacuum at 50°C for 12 h. 2.3. Preparation of the PVDF/CNT/Co composite films The flexible PVDF/CNT/Co(chains or flowers) composite films were prepared by the methods of solution processing and compression molding.45-47 Figure 1 shows a schematic illustration about the preparation process of ternary PVDF/CNT/Co composite films. Typically, the DMF solution comprising PVDF was fabricated, and 6 wt% MWCNT were uniformly dispersed in the mixture via magnetic stirring. Then, ultrasonication was used for the mixture of Co particles. The flexible PVDF/CNT/Co composite films were finally obtained by evaporating and compression molding process.. To investigate the effects of Co filler content and Co anisotropy shape on the performances of EC, TC and electromagnetic shielding, a series of PVDF/6 wt%-CNT/Co composite films were prepared as follows, i.e.,1 wt% Co chains, 3 wt% Co chains, 6 wt% Co


Page 7 of 34 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


chains, 1 wt% Co flowers, 3 wt% Co flowers, and 6 wt% Co flowers, which were denoted as CoC-1, Co-C-3, Co-C-6, Co-F-1, Co-F-3, and Co-F-6 samples, respectively. 2.4. Characterization The crystal structures of the prepared samples were examined by X-ray diffraction (XRD, Rigaku Ultima IV) using Cu Ka radiation (λ= 0.15418 nm). The Fourier transform infrared spectroscopy (FT-IR) spectra of the hybrid were obtained on a Nicolet iS10 FT-IR spectrometer (USA). The morphology and element mapping of these samples were observed using a field emission scanning electron microscope (FESEM, JEOL-7001F), equipped with an energydispersive X-ray spectrometer (EDS, Oxford, UK). XPS spectra was recorded on a Thermo ESCALAB 250 X-ray photoelectron spectrometer using a power source of Al Kα (1486.6 eV) monochromatic X-ray under a pressure of ∼2.0 × 10 − 7 Pa. The magnetic properties of these samples were measured by a vibrating sample magnetometer (VSM, Lakeshore 7400) at a room temperature. The EC of composite films were measured using a TH282A LCR Meter (Tonghui Electronic Co., Ltd, China) at a frequency of 1 kHz and a voltage of 1.0 volts. A hot disk thermal constant analyzer (TPS 2500, Them Test Inc., Sweden) with a transient plane source was employed to measure the TC of solid and foamed samples.48-49 Based on the recorded response of temperature, the TC of samples which were measured at a room temperature can be derived by using a built-in software. Tensile experiments of PVDF/CNTs/Co (flowers or chains) were carried out using a universal testing machine (UTM4204, china). Specimens for tensile test were compressed into dumbbell-shape with a volume of 27mm2mm1mm. It should be noted that three samples were prepared for each group to obtain a reliable mean value. At the room temperature, the tensile properties were measured in accordance to ASTM D638-10 with a crosshead speed of 50mm/min. The infrared thermal image of the samples in microwave radiation



Page 8 of 34

(domestic microwave oven, 2.45 GHz) was recorded on a VarioCAM high resolution (InfraTec GmbH, Germany). The EMI shielding properties were tested in a frequency range of 18.0~26.5 GHz (K-band) at room temperature using a vector network analyzer (VNA, Agilent N5234A), having two waveguide-to-coaxial adaptors connected face-to-face. A calibration was conducted on the VNA before the measurement of the S scattering parameter. Samples were cut into ∼10.6 mm × 4.3 mm (length × width) sizes to completely match up the waveguide holders. The physical parameters for evaluating the EMI performance, including SE total (SET), SE reflection (SER), and SE absorption

(SEA), can be obtained based on the scattering parameters (S11 and S21). 50-53

R  S11

2

(1)

T  S 21

2

(2)

SER  - log10 1- R 

(3)

 T  SE A  - log10    1- R 

(4)

SET  SER  SE A

(5)

3. Results and Discussion The as-received Co samples were analyzed using XRD, SEM and EDS techniques. As shown in Figure S1, for the Co chains, the diffracted peaks were attributed to a face-centered cubic phase (FCC, JCPDS no. 15-0806). As for the Co flowers, all the diffracted peaks were perfectively assigned to the hexagonal close packing (HCP, JCPDS no. 15-0806). The other characteristic impurity peaks were not appeared, indicating the pure phase of the as-obtained Co samples. The morphologies of synthesized Co samples were observed by FESEM, and the results were 8 ACS Paragon Plus Environment

Page 9 of 34 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


presented in Figure 2. From the Figure 2 (a1-a3), the Co chains with a length of ten to hundred µm present a unique one-dimensional structure, composing of spherical particles with an average diameter of 2 µm. On the whole, the typical Co flower products (Figure 2b1) show that the fabricated samples compose of flower-like architectures. The architectures distribute uniformly and their diameters are of ~6 µm. Magnified images reveal that these architectures are fomred by leaf-like flakes and each of them seems to grow from the same center (Figure 2(b2-b3)). Furthermore, it is noteworthy that the Co chains and Co flowers were only made up of Co element (Figure 2 (c1-c2, d1-d2)). Figure S2 exhibits the TEM image of the raw multi-walled carbon nanotubes (MWCNT). We can observe that the MWCNT were in a diameter of 10-15 nm and an average length of 1.5 µm. Figure 3 displays the XRD patterns of the pure PVDF AND as-received PVDF/CNT/Co(chains or flowers) flexible films with different Co-chain or Co-flower weights. Based on the XRD patterns of the PVDF/CNT/Co composite films, we can conclude that at least two points could be verified. Firstly, after the introduction of CNT and Co samples, part of α-PVDF can transform into β-phase PVDF. This is in a good agreement with other reports in which the addition of filler would cause a phase transition from α to β PVDF.

54

Secondly, when the Co-chain and Co-

flower contents were higher than 6 wt%, the diffracted peaks of the fcc Co and hcp Co crystals could be seen, respectively. On the basis of the above confirms, we concluded that the composite films consisted of the α+β phases of the PVDF, the CNT and the crystal Co. In order to further confirm the α- and β-phases in the PVDF/CNT/Co composite films, the Fourier transform infrared (FTIR) spectra were provided in Figure S3a. The absorbance bands at 766 cm-1 (CF2 skeletal bending), 795 and 976 cm-1 (CH2 rocking) were attributed to nonpolar α-phase.55 The absorbance band at 870 resulted from the β-phase, which was assigned to the CH2 and CF2 9 ACS Paragon Plus Environment


Page 10 of 34

groups generated from the CH2 rocking, CF2 stretching and skeletal C–C stretching.56 The bending of C–C–C appeared at 1070 cm-1.49 Therefore, based on the results of XRD and FT-IR, we can conclude that the α- and β-phases of PVDF co-existed in PVDF/CNT/Co composite films. To investigate whether the bonds between PVDF, CNT and Co were formed, XPS analysis was conducted. The C 1s XPS spectrum (Figure S3b) can be deconvoluted into four peaks at 284.6, 286.5, 289.6 and 290.6 eV, which correspond to C-C, C-O, -CF2-CH2-, (-CF2-CF2-), respectively. The C-O bands belong to the some defectives in the raw CNT. Therefore, the CNT and Co particles just physically distributed in the PVDF matrix without formation any chemical bonds. To intuitively observe the distribution of CNT and Co in polymer matrix, the fractured crosssection of the PVDF/CNT/Co composite films were examined by the SEM images (Figure 4). One can notice that all CNT and Co were uniformly distributed in the PVDF polymer. Moreover, with increasing Co contents, more Co chains (Figure 4a-c) and Co flowers (Figure 4d-f) could be observed in the same magnification SEM area. Furthermore, the elemental mappings of PVDF/CNT/Co composite films were carried out and the results were shown in Figure 5. We can clearly find that the Co element (Co chains or flowers), C element (PVDF and CNT) and F element (PVDF) co-exist in the SEM area, which suggests that Co chains or flowers, and CNT were evenly dispersed in PVDF polymer. Figure S4 shows a field dependence of magnetization for the Ni@NG/NC nanosheets at a room temperature. The saturation magnetization (Ms) values of Co-C-1, Co-F-1, Co-C-3, Co-F-3, CoC-6, and Co-F-6 samples are 1.74, 0.98, 2.12, 1.48, 2.28, and 2.06 emu g − 1, respectively. Such low value of Ms was attributed to the low concentration of Co (chains or flowers) in the PVDF/CNT/Co composite films. Additionally, the PVDF/CNT/Co composite films with Co chains exhibited higher Ms values than counterparts with same content of Co flowers, which is 10 ACS Paragon Plus Environment

Page 11 of 34 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


due to the higher anisotropy of Co chains than Co flowers.

57

As an important role on the EMI

shielding performance, the EC of prepared composite was further examined for a better understanding of the shielding efficiency.

58-59

Figure 6 shows the variation in EC of the as-

received PVDF/CNT/Co(chains or flowers) flexible films with different Co contents. It can be found that the EC of PVDF/CNT/Co (chains or flowers) flexible films increase with an increase of Co contents. Moreover, the Co-chain and Co-flower contents at 6 wt% display the high conductivity value of 2.28 S/cm (228 S/m) and 1.94 S/cm (194 S/m), respectively. These high electrical conductivities are beneficial for the enhancement of EMI shielding.

60-61

Higher

conductivity generally conduces to higher EMI shielding performance for two reasons: one hand, higher conductivity causes more impendence mismatch between ambient space and film interface, resulting in a higher reflection at interfaces; on the other hand, when electromagnetic waves spread through the film material, higher conductivity would induce more currents, converting electromagnetic energy into heat. As a result, the synergistic effect of improved reflection and dissipation capability contributes the conductive materials with enhanced performance of EMI shielding significantly. 62-63 The EMI shielding effectiveness (SE) is used to determine the ability of material to block incoming electromagnetic waves. Generally, an SE value of 30 decibels (dB) corresponding to 99.9% attenuation of EM radiation is deemed to be a sufficient level of shielding. Figure 7a reveals the EMI SET for PVDF/ CNT/Co(chains or flowers) flexible films with different Co concentrations and a thickness of 0.3 mm over a range of 18.0~26.5 GHz. Because of the weak dependence of SET’s frequency on the measured range, the average EMI SE was utilized for the evaluation of EMI shielding properties. The EMI SET’s values tend to increase significantly with the increasing concentration of Co. For example, for the PVDF/CNT/Co-chain and 11 ACS Paragon Plus Environment


Page 12 of 34

PVDF/CNT/Co-flower flexible films with same content of 3 wt%, the average SET of 29.5 dB and 30.1 dB were obtained respectively, reaching a target level of 30 dB for industrial applications.64 If the contents of Co-chain and Co-flower were continually increased to 6 wt%, the average SET values of composite films were 35.3 dB and 32.2 dB, respectively. This enhancement in SET was largely attributed to the boosted EC. The growing Co chains or flowers provide a strengthened conductive interface between CNT and PVDF, causing close interactions with the incoming microwaves and eventually improving the EMI shielding performance.39, 65 Interestingly, with the same Co content, the EMI SE value of PVDF/CNT/Co-chain is superior to that of PVDF/CNT/Co-flower, which can be attributed to the following reasons. Firstly, the magnetic property of Co chain is superior to that of Co flower, which can cause much more magnetic loss. Secondly, the Co chain was beneficial for the EC of PVDF matrix than Co flowers, thus it can improve EMI shielding performance. Thirdly, due to the unique onedimensional chain-like structure, the Co chains could cause orientation polarization, and could regard as the microwave receiver to dissipate more microwaves.

66-67

To reveal the effects of

CNT and Co, Figure S5 demonstrates the EMI shielding properties of various PVDFs based different composites. For the PVDF/Co chain composite, the EMI SE values were significantly enhanced with the addition of CNT. For the PVDF/CNT composite, the EMI shielding properties were improved as the Co chain increases, but increasing rate was smaller than that of CNT. Thus, we can conclude that the CNT plays a vital role in the enhancemnt of the EMI shielding properties of PVDF/CNT/Co composite. The enhanced EMI shielding properties was associated with the high EC provided by CNT rather than Co particles. Thanks to the magnetic properties of Co chain, the magnetic loss of Co can also partly contribute to EMI shielding properties.


Page 13 of 34 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 understand the shielding mechanism of the fabricated PVDF/CNT/Co(chains or flowers) flexible films, the average SER and SEA values of the PVDF/CNT/Co(chains or flowers) flexible films with a 0.3 mm film thickness were calculated (Figure 7b). Intuitively, the SEA values significantly overpass the SER values for the whole PVDF/CNT/Co (chains or flowers) flexible films. For instance, the average SET, SEA, and SER values of the PVDF/CNT/Co (6 wt% Co chains) flexible film were 35.3, 26.2, and 9.1 dB, respectively. As a result, the contribution of absorption to the EMI SET was 73.5% in comparison with that of reflection which indicates that absorption, played a dominated role on the contribution of shielding incoming microwave rather than reflection regarding the PVDF/CNT/Co flexible films. To clearly observe the effect of Co increase on the SEA mechanism, we caculated the percentage (SEA/SET) of each samples and the result was shown in the inset of Figure 7b. Interestingly, as the Co content increased, the percentage (SEA/SET) values display a feeble decline tendency, which indicates that the increase of Co content could not contribute to the SEA in the EMI shielding properties. The reason is that the EC was improved when the Co particles were added, which enhaced the reflection mechanism. However, by analysis of these SEA/SET values, one can notice that the EMI shielding properties mainly resulted from the absorption instead of reflection. Such absorptiondominated microwave shielding satisfied the current requirement of EMI shielding, which can decrease less second microwave pollution causing by the reflection. 68 The absorption-dominated EMI shielding property is strongly dependent on the CNT addition rather than Co addition. Seen from the Figure S6, one can notice that the PVDF/5 wt% Co (flower or chain) composites present inferior EMI shielding properties compared with the counterpart with the introduction of 6 wt% CNT. This is because that the conductive network was not formed in the PVDF/5 wt% Co (flower or chain) composites. In PVDF/CNT/Co composites, due to the high content of CNT, the



Page 14 of 34

conductive networks happened. Thus, the EMI shielding properties are mainly originated from the CNT addition, and the EMI shielding mostly results from absorption, which was caused by conduction loss from CNT conductive network. When the magnetic Co powders were introduced into PVDF/CNT system, magnetic loss was produced under alternated electromagnetic field. This will make certin contribution to absorption mechasim. Thus, the absorption-dominated EMI shielding property is strongly dependent on the CNT addition rather than Co addition. It is well anticipated that the incident microwave was reflected, after being scattered and absorbed several times at the interfaces between polymer and conductive layers.21,

69

A large

interface area is expected to induce high EMI SE. Thus, we calculated the EMI SE for the PVDF/CNT/Co (6 wt% Co chains) with different thickness as shown in Figure 8a. The EMI SET continuously increased throughout the frequency range, with the thickness increasing from 0.25 to 0.40 mm. The average EMI SET values of the PVDF/CNT/Co (6 wt% Co chains) flexible films with thicknesses of 0.25, 0.30, 0.35 and 0.40mm were obtained as 28.8, 35.3, 39.9 and 45.7dB, respectively. To investigate the attenuation mechanism of PVDF/CNT/Co (6 wt% Co chains) flexible films, the average SET, SER, and SEA of samples with different thicknesses are demonstrated in Figure 8b. SET and SEA both increased with the thickness while the SER nearly keep constant. The increased EMI SE is mainly attributed to the enhancement of SEA. The contribution of absorption to the EMI SET increases from 68.8% for 0.25 mm to 80.1% for 0.4 mm, which demonstrates the absorption-dominated shielding mechanism. We also investigated the influence of composite's thickness on the EMI shielding properties of PVDF/ CNT/Co (6 wt% Co flowers). Figure 8 (c,d) display the SET and, average SET, SER and SEA values of the PVDF/CNT/Co (6 wt% Co flowers) with different thicknesses in the frequency range of 18.026.5 GHz. Similarly, with incresing the thickness, the SET values enhanced correspondingly 14 ACS Paragon Plus Environment

Page 15 of 34 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


(Figure 8c). By analysis of the average SET, SER and SEA values of the PVDF/CNT/Co (6 wt% Co flowers) in various thicknesses, one can find that, the absorption mechanism mainly contributed to the EMI shielding properties (Figure 8d). The mechanical properties of PVDF/CNTs/Co (flowers or chains) were studied. Figure S7 gives the tensile strength and elastic modulus of PVDF/CNTs/Co (flowers or chains) with different Co filler contents. With the increase of Co filler content, the tensile strength and elastic modulus increased slightly due to the low fill of Co. Therefore, the Co filler is beneficial to increase the structural strength of PVDF/CNTs/Co (flowers or chains), but it also reduced the toughness of composite. With the same Co content, the tensile strength of PVDF/CNTs/Co-chain is superior to that of PVDF/CNTs/Co-flower, and the elastic modulus of Co-chain filler is higher than that of Co-flower filler, which is resulted from the structural stress and frangibility of onedimensional chain-like structure. In general, the typical EM shielding devices incline to overheat when exposure to microwave radiation for a long time.41-42 For the further miniaturization of a variety of electronic interfaces, an integrated thermal control mechanism becomes necessary. High heat dissipation would take place in the composite materials with high TC.

70-72

Combining high EC/TC of the

PVDF/CNT/Co(chains or flowers) flexible films with a small weight fraction of MWCNT (6%), the heat dissipation ability can be improved because of the carbonic contents. It is well known that CNT display excellent TC (κ) which can be as high as 2000−6000 W/(mK).73 Figure 9 exhibits the TC of the PVDF/CNT/Co(chains or flowers) flexible films at room temperature. Compared with reported pure PVDF (0.21 W/(mK)),

42, 47

the PVDF-based composite flexible

films' TC were significantly increased after the introduction of the Co and the CNT. Moreover,



Page 16 of 34

with increasing Co contents, the TC increased correspondingly, which is due to the high TC of metal Co sample. Interestingly, with the same Co contents, the TC of PVDF/CNT/Co-chain is higher than that of PVDF/CNT/Co-flowers. Such phenomenon was due to the shape anisotropy.74 In fact, heat could quickly diffuse through the crystal filler. Benefiting from the filler, we can obtain the high TC. It indicates that the increasing length of the filler would enhance the TC of composite material in the filler’s direction (anisotropic property).75 76 Thus, it seems that Co chain is the best choice to obtain high TC composites. The TCs of the Co-C-6 and Co-F-6 composites were obtained as 1.39 W/(mK) and 1.30 W/(m K), being an increase of 562% and 519%, respectively, compared with that of neat PVDF. Such high TC favors to dissipate microwave energy by the method of Joule heating. 77 To directly evaluate the thermal properties of PVDF/CNT/Co(chains or flowers) flexible films during microwave irradiation, we used infrared camera to observe the temperature variation under microwave irradiation. Figure 10a displayed the schematic illustration of the thermal properties measured by infrared camera under microwave irradiation. Firstly, we placed the PVDF composites films under microwave oven irradiated by microwave in constant time (2s), and the surface temperature could reach 110 ºC, which indicaes high absorption microwave energy and fast transformation between microwave enerny and heat. Then we stopped microwave irradiation and observe the change of temperature. The temperature distribution of the top surfaces of PVDF/CNT/Co(chains or flowers) flexible films was monitored using an infrared (IR) camera, and the temperature−time profiles of the PVDF/CNT/Co(chains or flowers) flexible films after stopping microwave irradiation are presented in Figure S8. The PVDF/CNT/Co-chains composite films revealed faster heat conduction with a temperature decrease rate than the PVDF/CNT/Co-flower composite films, which is due to higher TC. 16 ACS Paragon Plus Environment

Page 17 of 34 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


Furthermore, the infrared images of the Co-C-6 and Co-F-6 samples at different time interval (1s, 2s, 3s and 4s) after stopping microwave irradiation show the quick heat dissipation behavior. At first stage (1s and 2s), more heat energy was dissipated, which causes huge temperature change, and temperature decreased from about 110 ºC to 70 ºC, as shown in Figure 10(b1-b2, c1-c2). At the second stage (3s and 4s), the temperature slowly decreased to about 50 ºC (Figure 10(b3-b4, c3-c4)). Therefore, it can be ascertained that these PVDF/CNT/Co(chains or flowers) flexible films provide new-era thin EM shielding films with enhanced SE and excellent TC, which are promising for multifaceted applications. Based on the results demonstrated above, we present a mechanism to illustrate the exceptionally high EMI shielding performance of the flexible PVDF/CNT/Co-chain and PVDF/CNT/Coflower composite films (Figure 11). Firstly, the flexible composite films is characterized with a high EC, generating a conduction loss irradiated by alternated electromagnetic field, which corresponded to the energy reduction through current flows via the mechanisms of conduction, hopping, and tunneling.

63, 69

Secondly, the interfaces among CNT, Co samples, and PVDF

matrix could induce polarization loss under an electromagnetic field.78-79 This occurs in a heterogeneous interface and was originated from accumulated charge.80-82 Next, the magnetic loss due to the Co samples, including natural resonance and eddy-current loss, favors the attenuation of the EM energy.

83-84

Finally, the special one-dimensional structure (Co chains) is

also beneficial to improve the microwave attenuation. Thereafter, Co chains would be considered as an excellent microwave receiver and to induce a point charge for dissipating the microwave energy and also an orientation polarization loss. 85 4. Conclusion



Page 18 of 34

We prepared a series of PVDF/CNT/Co(chains or flowers) flexible films and found that their EC, TC and EMI shielding properties can be significantly enhanced by increasing the Co contents. Due to the shape anisotropy of Co samples, at the same contents, PVDF/CNT/Co-chain exhibited higher EC, EMI SE value, and TC than those of PVDF/CNT/Co-flower samples. For the PVDF/CNT/Co-chain (6 wt% Co chains) and PVDF/CNT/Co-flower (6 wt% Co flowers) flexible films at a thickness of 0.3 mm, the SET values reached 35.3 dB and 32.2 dB, respectively. Moreover, the EMI shielding performances of PVDF/CNT/Co(chains or flowers) flexible films can be effectively controlled by tuning the films’ thicknesses. Based on the analysis of EMI shielding mechanism, it is indicated that the absorption plays a dominant role on the EMI shielding performance. Besides, the PVDF/CNT/Co(chains or flowers) flexible films with high TC has an advantage in the dissipation of microwave energy through Joule heating effect. Consequently, these flexible PVDF/CNT/Co(chains or flowers) conductive films can be utilized as high-efficiency EMI shielding materials, featured with heat dissipation capability for long service lifetime. Supporting Information XRD patterns of Co samples (chain and flowers), TEM image of raw CNT, FT-IR spectra, magnetic hysteresis loops, the tensile strength and elastic modulus, stress-strain curves and temperature−time profiles of the PVDF/CNT/Co(chains or flowers) flexible films, C1s core level XPS spectrum of PVDF/CNT/Co-chains (6wt%), and EMI shielding properties of various PVDF based composites. Acknowledgements


Page 19 of 34 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


The research work was supported by the National Natural Science Foundation of China (51675489, 51802289), the Natural Science Foundation of Zhejiang Province (LY18E050011) and Key Science and Technology Program of Henan Province (182102210108). References: 1.

Han, M.; Yin, X.; Hou, Z.; Song, C.; Li, X.; Zhang, L.; Cheng, L., Flexible and Thermostable

Graphene/SiC Nanowire Foam Composites with Tunable Electromagnetic Wave Absorption Properties. ACS Appl. Mater. Interfaces 2017, 9 (13), 11803-11810. 2.

Sun, H.; Che, R.; You, X.; Jiang, Y.; Yang, Z.; Deng, J.; Qiu, L.; Peng, H., Cross-Stacking Aligned

Carbon-Nanotube Films to Tune Microwave Absorption Frequencies and Increase Absorption Intensities. Adv. Mater. 2014, 26 (48), 8120-8125. 3.

Zhao, B.; Shao, G.; Fan, B.; Zhao, W.; Xie, Y.; Zhang, R., Synthesis of Flower-Like CuS Hollow

Microspheres Based on Nanoflakes Self-Assembly and Their Microwave Absorption Properties. J. Mater. Chem. A 2015, 3 (19), 10345-10352. 4.

Zhao, B.; Shao, G.; Fan, B.; Zhao, W.; Zhang, R., Investigation of the Electromagnetic Absorption

Properties of Ni@TiO2 and Ni@SiO2 Composite Microspheres with Core-Shell Structure. Phys. Chem. Chem. Phys. 2015, 17 (4), 2531-2539. 5.

Zhao, B.; Shao, G.; Fan, B.; Wang, C.; Xie, Y.; Zhang, R., Preparation and Enhanced Microwave

Absorption Properties of Ni Microspheres Coated with Sn6O4(OH)4 Nanoshells. Powder Technol. 2015, 270, 20-26. 6.

Wu, N.; Qiao, J.; Liu, J.; Du, W.; Xu, D.; Liu, W., Strengthened Electromagnetic Absorption

Performance Derived from Synergistic Effect of Carbon Nanotube Hybrid with Co@C Beads. Adv. Compos. Hybrid Mater. 2018, 1 (1), 149-159. 7.

Wu, N.; Liu, C.; Xu, D.; Liu, J.; Liu, W.; Shao, Q.; Guo, Z., Enhanced Electromagnetic Wave

Absorption of Three-Dimensional Porous Fe3O4/C Composite Flowers. ACS Sustain. Chem. Eng. 2018, 6 (9), 12471-12480. 8.

Zhao, B.; Guo, X.; Zhao, W.; Deng, J.; Fan, B.; Shao, G.; Bai, Z.; Zhang, R., Facile Synthesis of

Yolk–Shell Ni@Void@SnO2(Ni3Sn2) Ternary Composites via Galvanic Replacement/Kirkendall Effect and Their Enhanced Microwave Absorption Properties. Nano Res. 2017, 10 (1), 331-343. 9.

Zhang, K.; Li, G.-H.; Feng, L.-M.; Wang, N.; Guo, J.; Sun, K.; Yu, K.-X.; Zeng, J.-B.; Li, T.; Guo, Z.;

Wang, M., Ultralow Percolation Threshold and Enhanced Electromagnetic Interference Shielding in Poly(Llactide)/Multi-Walled Carbon Nanotube Nanocomposites with Electrically Conductive Segregated Networks. J. Mater. Chem. C 2017, 5 (36), 9359-9369.



10.

Page 20 of 34

Zhao, B.; Deng, J.; Zhang, R.; liang, L.; Fan, B.; Bai, Z.; Shao, G.; Park, B. C., Recent Advances on

the Electromagnetic Wave Absorption Properties of Ni Based Materials. Eng. Sci. 2018, 3, 5-40. 11.

Wang, Z.; Wei, R.; Liu, X., Fluffy and Ordered Graphene Multilayer Films with Improved

Electromagnetic Interference Shielding over X-Band. ACS Appl. Mater. Interfaces 2017, 9 (27), 22408-22419. 12. Cao,

Sun, K.; Xie, P.; Wang, Z.; Su, T.; Shao, Q.; Ryu, J.; Zhang, X.; Guo, J.; Shankar, A.; Li, J.; Fan, R.; D.;

Guo,

Z.,

Flexible

Polydimethylsiloxane/Multi-Walled

Carbon

Nanotubes

Membranous

Metacomposites with Negative Permittivity. Polymer 2017, 125, 50-57. 13.

Xie, P.; Li, H.; He, B.; Dang, F.; Lin, J.; Fan, R.; Hou, C.; Liu, H.; Zhang, J.; Ma, Y.; Guo, Z., Bio-

Gel Derived Nickel/Carbon Nanocomposites with Enhanced Microwave Absorption. J. Mater. Chem. C 2018, 6 (32), 8812-8822. 14.

Ameli, A.; Nofar, M.; Wang, S.; Park, C. B., Lightweight Polypropylene/Stainless-Steel Fiber

Composite Foams with Low Percolation for Efficient Electromagnetic Interference Shielding. ACS Appl. Mater. Interfaces 2014, 6 (14), 11091-11100. 15.

Zhao, B.; Zhao, W.; Shao, G.; Fan, B.; Zhang, R., Morphology-Control Synthesis of a Core–Shell

Structured NiCu Alloy with Tunable Electromagnetic-Wave Absorption Capabilities. ACS Appl. Mater. Interfaces 2015, 7 (23), 12951-12960. 16.

Zhang, Y.; Qiu, M.; Yu, Y.; Wen, B.; Cheng, L., A Novel Polyaniline-Coated Bagasse Fiber

Composite with Core–Shell Heterostructure Provides Effective Electromagnetic Shielding Performance. ACS Appl. Mater. Interfaces 2017, 9 (1), 809-818. 17.

Ameli, A.; Jung, P. U.; Park, C. B., Through-Plane EC of Injection-Molded Polypropylene/Carbon-

Fiber Composite Foams. Compos. Sci. Technol. 2013, 76, 37-44.. 18.

Zhou, B.; Li, Y.; Zheng, G.; Dai, K.; Liu, C.; Ma, Y.; Zhang, J.; Wang, N.; Shen, C.; Guo, Z.,

Continuously Fabricated Transparent Conductive Polycarbonate/Carbon Nanotube Nanocomposite Films for Switchable Thermochromic Applications. J. Mater. Chem. C 2018, 6 (31), 8360-8371. 19.

Al-Saleh, M. H.; Sundararaj, U., Electromagnetic Interference Shielding Mechanisms of

CNT/Polymer Composites. Carbon 2009, 47 (7), 1738-1746. 20.

Chen, Y.; Zhang, H.-B.; Yang, Y.; Wang, M.; Cao, A.; Yu, Z.-Z., High-Performance Epoxy

Nanocomposites Reinforced with Three-Dimensional Carbon Nanotube Sponge for Electromagnetic Interference Shielding. Adv. Funct. Mater. 2016, 26 (3), 447-455. 21.

Zeng, Z.; Chen, M.; Jin, H.; Li, W.; Xue, X.; Zhou, L.; Pei, Y.; Zhang, H.; Zhang, Z., Thin and

Flexible Multi-Walled Carbon Nanotube/Waterborne Polyurethane Composites with High-Performance Electromagnetic Interference Shielding. Carbon 2016, 96, 768-777. 22.

Li, C.; Yang, G.; Deng, H.; Wang, K.; Zhang, Q.; Chen, F.; Fu, Q., The Preparation and Properties of

Polystyrene/Functionalized Graphene Nanocomposite Foams Using Supercritical Carbon Dioxide. Polym. Int. 2013, 62 (7), 1077-1084.


Page 21 of 34 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.

Yan, D.-X.; Ren, P.-G.; Pang, H.; Fu, Q.; Yang, M.-B.; Li, Z.-M., Efficient Electromagnetic

Interference Shielding of Lightweight Graphene/Polystyrene Composite. J. Mater. Chem. 2012, 22 (36), 18772-18774. 24.

Liu, H.; Li, Y.; Dai, K.; Zheng, G.; Liu, C.; Shen, C.; Yan, X.; Guo, J.; Guo, Z., Electrically

Conductive Thermoplastic Elastomer Nanocomposites at Ultralow Graphene Loading Levels for Strain Sensor Applications. J. Mater. Chem. C 2016, 4 (1), 157-166. 25.

Liu, H.; Huang, W.; Yang, X.; Dai, K.; Zheng, G.; Liu, C.; Shen, C.; Yan, X.; Guo, J.; Guo, Z.,

Organic Vapor Sensing Behaviors of Conductive Thermoplastic Polyurethane–Graphene Nanocomposites. J. Mater. Chem. C 2016, 4 (20), 4459-4469. 26.

Liu, H.; Dong, M.; Huang, W.; Gao, J.; Dai, K.; Guo, J.; Zheng, G.; Liu, C.; Shen, C.; Guo, Z.,

Lightweight Conductive Graphene/Thermoplastic Polyurethane Foams with Ultrahigh Compressibility for Piezoresistive Sensing. J. Mater. Chem. C 2017, 5 (1), 73-83. 27.

Guan, X.; Zheng, G.; Dai, K.; Liu, C.; Yan, X.; Shen, C.; Guo, Z., Carbon Nanotubes-Adsorbed

Electrospun PA66 Nanofiber Bundles with Improved Conductivity and Robust Flexibility. ACS Appl. Mater. Interfaces 2016, 8 (22), 14150-14159. 28.

He, Y.; Yang, S.; Liu, H.; Shao, Q.; Chen, Q.; Lu, C.; Jiang, Y.; Liu, C.; Guo, Z., Reinforced Carbon

Fiber Laminates with Oriented Carbon Nanotube Epoxy Nanocomposites: Magnetic Field Assisted Alignment and Cryogenic Temperature Mechanical Properties. J. Colloid Interface Sci. 2018, 517, 40-51. 29.

Wang, C.; Zhao, M.; Li, J.; Yu, J.; Sun, S.; Ge, S.; Guo, X.; Xie, F.; Jiang, B.; Wujcik, E. K.; Huang,

Y.; Wang, N.; Guo, Z., Silver Nanoparticles/Graphene Oxide Decorated Carbon Fiber Synergistic Reinforcement in Epoxy-Based Composites. Polymer 2017, 131, 263-271. 30.

Lin, C.; Hu, L.; Cheng, C.; Sun, K.; Guo, X.; Shao, Q.; Li, J.; Wang, N.; Guo, Z., Nano-

TiNb2O7/Carbon Nanotubes Composite Anode for Enhanced Lithium-Ion Storage. Electrochim. Acta 2018, 260, 65-72. 31.

Song, B.; Wang, T.; Sun, H.; Shao, Q.; Zhao, J.; Song, K.; Hao, L.; Wang, L.; Guo, Z., Two-Step

Hydrothermally

Synthesized

Carbon

Nanodots/WO3

Photocatalysts

with

Enhanced

Photocatalytic

Performance. Dalton Trans. 2017, 46 (45), 15769-15777. 32.

Su, T.; Shao, Q.; Qin, Z.; Guo, Z.; Wu, Z., Role of Interfaces in Two-Dimensional Photocatalyst for

Water Splitting. ACS Catalysis 2018, 8 (3), 2253-2276. 33.

Wang, X.; Zeng, X.; Cao, D., Biomass-Derived Nitrogen-Doped Porous Carbons (NPC) and

NPC/Polyaniline Composites as High Performance Supercapacitor Materials. Eng. Sci. 2018, 1, 1-23.. 34.

Cheng, C.; Fan, R.; Wang, Z.; Shao, Q.; Guo, X.; Xie, P.; Yin, Y.; Zhang, Y.; An, L.; Lei, Y.; Ryu, J.

E.; Shankar, A.; Guo, Z., Tunable and Weakly Negative Permittivity in Carbon/Silicon Nitride Composites with Different Carbonizing Temperatures. Carbon 2017, 125, 103-112.



35.

Page 22 of 34

Xie, P.; Wang, Z.; Zhang, Z.; Fan, R.; Cheng, C.; Liu, H.; Liu, Y.; Li, T.; Yan, C.; Wang, N.; Guo, Z.,

Silica Microsphere Templated Self-Assembly of a Three-Dimensional Carbon Network with Stable RadioFrequency Negative Permittivity and Low Dielectric Loss. J. Mater. Chem. C 2018, 6 (19), 5239-5249. 36.

Mural, P. K. S.; Pawar, S. P.; Jayanthi, S.; Madras, G.; Sood, A. K.; Bose, S., Engineering

Nanostructures by Decorating Magnetic Nanoparticles onto Graphene Oxide Sheets to Shield Electromagnetic Radiations. ACS Appl. Mater. Interfaces 2015, 7 (30), 16266-16278. 37.

Menon Aishwarya, V.; Madras, G.; Bose, S., Magnetic Alloy‐MWNT Heterostructure as Efficient

Electromagnetic Wave Suppressors in Soft Nanocomposites. ChemistrySelect 2017, 2 (26), 7831-7844. 38.

Biswas, S.; Panja, S. S.; Bose, S., Unique Multilayered Assembly Consisting of “Flower-Like” Ferrite

Nanoclusters Conjugated with MWCNT as Millimeter Wave Absorbers. J. Phys. Chem. C 2017, 121 (26), 13998-14009. 39.

Lee, S.-H.; Kang, D.; Oh, I.-K., Multilayered Graphene-Carbon Nanotube-Iron Oxide Three-

Dimensional Heterostructure for Flexible Electromagnetic Interference Shielding Film. Carbon 2017, 111, 248-257. 40.

Dreyer, D. R.; Park, S.; Bielawski, C. W.; Ruoff, R. S., The Chemistry of Graphene Oxide. Chem. Soc.

Rev. 2010, 39 (1), 228-240. 41.

Lee, S. H.; Yu, S.; Shahzad, F.; Kim, W. N.; Park, C.; Hong, S. M.; Koo, C. M., Density-Tunable

Lightweight Polymer Composites with Dual-Functional Ability of Efficient EMI Shielding and Heat Dissipation. Nanoscale 2017, 9 (36), 13432-13440. 42.

Arief, I.; Biswas, S.; Bose, S., FeCo-Anchored Reduced Graphene Oxide Framework-Based Soft

Composites Containing Carbon Nanotubes as Highly Efficient Microwave Absorbers with Excellent Heat Dissipation Ability. ACS Appl. Mater. Interfaces 2017, 9 (22), 19202-19214. 43.

Hu, M. J.; Lin, B.; Yu, S. H., Magnetic Field-Induced Solvothermal Synthesis of One-Dimensional

Sssemblies of Ni-Co Alloy Microstructures. Nano Res. 2008, 1 (4), 303-313. 44.

Tong, G.; Yuan, J.; Wu, W.; Hu, Q.; Qian, H.; Li, L.; Shen, J., Flower-Like Co Superstructures:

Morphology and Phase Evolution Mechanism and Novel Microwave Electromagnetic Characteristics. CrystEngComm 2012, 14 (6), 2071-2079. 45.

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. Interfaces 2017, 9 (24), 20873-20884. 46.

Zhao, B.; Wang, S.; Zhao, C.; Li, R.; Hamidinejad, S. M.; Kazemi, Y.; Park, C. B., Synergism

Between Carbon Materials and Ni Chains in Flexible Poly(Vinylidene Fluoride) Composite Films with High Heat Dissipation to Improve Electromagnetic Shielding Properties. Carbon 2018, 127, 469-478. 47.

Zhao, B.; Park, C. B., Tunable Electromagnetic Shielding Properties of Conductive Poly(Vinylidene

Fluoride)/Ni Chain Composite Films with Negative Permittivity. J. Mater. Chem. C 2017, 5 (28), 6954-6961.


Page 23 of 34 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


48.

Zhao, J.; Zhao, Q.; Wang, C.; Guo, B.; Park, C. B.; Wang, G., High Thermal Insulation and

Compressive Strength Polypropylene Foams Fabricated by High-Pressure Foam Injection Molding and Mold Opening of Nano-Fibrillar Composites. Mater. Des. 2017, 131, 1-11. 49.

Zhao, B.; Zhao, C.; Wang, C.; Park, C. B., Poly(Vinylidene Fluoride) Foams: a Promising Low-k

Dielectric and Heat-Insulating Material. J. Mater. Chem. C 2018, 6 (12), 3065-3073. 50.

Shen, B.; Li, Y.; Yi, D.; Zhai, W.; Wei, X.; Zheng, W., Strong Flexible Polymer/Graphene Composite

Films with 3D Saw-Tooth Folding for Enhanced and Tunable Electromagnetic Shielding. Carbon 2017, 113, 55-62. 51.

Yuan, Y.; Yin, W.; Yang, M.; Xu, F.; Zhao, X.; Li, J.; Peng, Q.; He, X.; Du, S.; Li, Y., Lightweight,

Flexible and Strong Core-Shell Non-Woven Fabrics Covered by Reduced Graphene Oxide for HighPerformance Electromagnetic Interference Shielding. Carbon 2018, 130, 59-68. 52.

Jung, J.; Lee, H.; Ha, I.; Cho, H.; Kim, K. K.; Kwon, J.; Won, P.; Hong, S.; Ko, S. H., Highly

Stretchable and Transparent Electromagnetic Interference Shielding Film Based on Silver Nanowire Percolation Network for Wearable Electronics Applications. ACS Appl. Mater. Interfaces 2017, 9 (51), 4460944616. 53.

Song, Q.; Ye, F.; Yin, X.; Li, W.; Li, H.; Liu, Y.; Li, K.; Xie, K.; Li, X.; Fu, Q.; Cheng, L.; Zhang, L.;

Wei, B., Carbon Nanotube–Multilayered Graphene Edge Plane Core–Shell Hybrid Foams for Ultrahigh‐Performance Electromagnetic‐Interference Shielding. Adv. Mater. 2017, 29 (31), 1701583. 54.

Wan, C.; Bowen, C. R., Multiscale-Structuring of Polyvinylidene Fluoride for Energy Harvesting: the

Impact of Molecular-, Micro- and Macro-structure. J. Mater. Chem. A 2017, 5 (7), 3091-3128. 55.

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 (3), 922-925. 56.

Thakur, P.; Kool, A.; Bagchi, B.; Hoque, N. A.; Das, S.; Nandy, P., Improvement of Electroactive β

Phase Nucleation and Dielectric Properties of WO3-H2O Nanoparticle Loaded Poly(Vinylidene Fluoride) Thin Films. RSC Adv. 2015, 5 (77), 62819-62827. 57.

Yang, P.; Zhao, X.; Liu, Y.; Gu, Y., Facile, Large-Scale, and Expeditious Synthesis of Hollow Co and

Co@Fe Nanostructures: Application for Electromagnetic Wave Absorption. J. Phys. Chem. C 2017, 121 (15), 8557-8568. 58.

Bera, R.; Maitra, A.; Paria, S.; Karan, S. K.; Das, A. K.; Bera, A.; Si, S. K.; Halder, L.; De, A.; Khatua,

B. B., An Approach to Widen the Electromagnetic Shielding Efficiency in PDMS/Ferrous Ferric Oxide Decorated RGO–SWCNH Composite Through Pressure Induced Tunability. Chem. Eng. J. 2018, 335, 501509. 59.

Zeng, Z.; Wang, C.; Zhang, Y.; Wang, P.; Seyed Shahabadi, S. I.; Pei, Y.; Chen, M.; Lu, X., Ultralight

and Highly Elastic Graphene/Lignin-Derived Carbon Nanocomposite Aerogels with Ultrahigh Electromagnetic Interference Shielding Performance. ACS Appl. Mater. Interfaces 2018, 10 (9), 8205-8213.



60.

Page 24 of 34

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. Interfaces 2018, 10 (9), 8245-8257. 61.

Zhou, E.; Xi, J.; Guo, Y.; Liu, Y.; Xu, Z.; Peng, L.; Gao, W.; Ying, J.; Chen, Z.; Gao, C., Synergistic

Effect of Graphene and Carbon Nanotube for High-Performance Electromagnetic Interference Shielding Films. Carbon 2018, 133, 316-322. 62.

Zhou, E.; Xi, J.; Liu, Y.; Xu, Z.; Guo, Y.; Peng, L.; Gao, W.; Ying, J.; Chen, Z.; Gao, C., Large-Area

Potassium-Doped Highly Conductive Graphene Films for Electromagnetic Interference Shielding. Nanoscale 2017, 9 (47), 18613-18618. 63.

Shahzad, F.; Alhabeb, M.; Hatter, C. B.; Anasori, B.; Man Hong, S.; Koo, C. M.; Gogotsi, Y.,

Electromagnetic Interference Shielding with 2D Transition Metal Carbides (MXenes). Science 2016, 353 (6304), 1137. 64.

Yan, D.-X.; Pang, H.; Li, B.; Vajtai, R.; Xu, L.; Ren, P.-G.; Wang, J.-H.; Li, Z.-M., Structured

Reduced Graphene Oxide/Polymer Composites for Ultra-Efficient Electromagnetic Interference Shielding. Adv. Funct. Mater. 2015, 25 (4), 559-566. 65.

Kong, L.; Yin, X.; Han, M.; Yuan, X.; Hou, Z.; Ye, F.; Zhang, L.; Cheng, L.; Xu, Z.; Huang, J.,

Macroscopic Bioinspired Graphene Sponge Modified with in-Situ Grown Carbon Nanowires and Its Electromagnetic Properties. Carbon 2017, 111, 94-102. 66.

Lv, H.; Ji, G.; Liang, X.; Zhang, H.; Du, Y., A Novel Rod-Like MnO2@Fe Loading on Graphene

Giving Excellent Electromagnetic Absorption Properties. J. Mater. Chem. C 2015, 3 (19), 5056-5064. 67.

Zhao, B.; Fan, B.; Shao, G.; Zhao, W.; Zhang, R., Facile Synthesis of Novel Heterostructure Based on

SnO2 Nanorods Grown on Submicron Ni Walnut with Tunable Electromagnetic Wave Absorption Capabilities. ACS Appl. Mater. Interfaces 2015, 7 (33), 18815-18823. 68.

Wu, Y.; Wang, Z.; Liu, X.; Shen, X.; Zheng, Q.; Xue, Q.; Kim, J.-K., Ultralight Graphene

Foam/Conductive Polymer Composites for Exceptional Electromagnetic Interference Shielding. ACS Appl. Mater. Interfaces 2017, 9 (10), 9059-9069. 69.

Shen, B.; Zhai, W.; Zheng, W., Ultrathin Flexible Graphene Film: An Excellent Thermal Conducting

Material with Efficient EMI Shielding. Adv. Funct. Mater. 2014, 24 (28), 4542-4548. 70.

Zhen, H.; Qing, S.; Yudong, H.; Long, Y.; Dayu, Z.; Xirong, X.; Jing, L.; Hu, L.; Zhanhu, G., Light

Triggered Interfacial Damage Self-Healing of Poly(P-phenylene Benzobisoxazole) Fiber Composites. Nanotechnology 2018, 29 (18), 185602. 71.

Sun, K.; Fan, R.; Zhang, X.; Zhang, Z.; Shi, Z.; Wang, N.; Xie, P.; Wang, Z.; Fan, G.; Liu, H.; Liu, C.;

Li, T.; Yan, C.; Guo, Z., An Overview of Metamaterials and Their Achievements in Wireless Power Transfer. J. Mater. Chem. C 2018, 6 (12), 2925-2943. 72.

Guo, Y.; Xu, G.; Yang, X.; Ruan, K.; Ma, T.; Zhang, Q.; Gu, J.; Wu, Y.; Liu, H.; Guo, Z.,

Significantly Enhanced and Precisely Modeled TC in Polyimide Nanocomposites with Chemically Modified


Page 25 of 34 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


Graphene via in Situ Polymerization and Electrospinning-Hot Press Technology. J. Mater. Chem. C 2018, 6 (12), 3004-3015. 73.

Huang, H.; Liu, C. H.; Wu, Y.; Fan, S., Aligned Carbon Nanotube Composite Films for Thermal

Management. Adv. Mater. 2005, 17 (13), 1652-1656. 74.

Burger, N.; Laachachi, A.; Ferriol, M.; Lutz, M.; Toniazzo, V.; Ruch, D., Review of TC in

Composites: Mechanisms, Parameters and Theory. Prog. Polym. Sci. 2016, 61, 1-28. 75.

Goyal, V.; Balandin, A. A., Thermal Properties of the Hybrid Graphene-Metal Nano-Micro-

Composites: Applications in Thermal Interface Materials. Appl. Phys. Lett. 2012, 100 (7), 073113. 76.

Kim, H. S.; Jang, J.-u.; Yu, J.; Kim, S. Y., TC of Polymer Composites Based on the Length of Multi-

Walled Carbon Nanotubes. Composites Part B 2015, 79, 505-512. 77.

Qin, F.; Brosseau, C., A Review and Analysis of Microwave Absorption in Polymer Composites

Filled with Carbonaceous Particles. J. Appl. Phys. 2012, 111 (6), 4. 78.

Xia, T.; Zhang, C.; Oyler, N. A.; Chen, X., Hydrogenated TiO2 Nanocrystals: A Novel Microwave

Absorbing Material. Adv. Mater. 2013, 25 (47), 6905-6910. 79.

Dong, J.; Ullal, R.; Han, J.; Wei, S.; Ouyang, X.; Dong, J.; Gao, W., Partially Crystallized TiO2 for

Microwave Absorption. J. Mater. Chem. A 2015, 3 (10), 5285-5288. 80.

Lv, H.; Zhang, H.; Ji, G.; Xu, Z. J., Interface Strategy To Achieve Tunable High Frequency

Attenuation. ACS Appl. Mater. Interfaces 2016, 8 (10), 6529-6538. 81.

Wang, H.; Xiang, L.; Wei, W.; An, J.; He, J.; Gong, C.; Hou, Y., Efficient and Lightweight

Electromagnetic Wave Absorber Derived from Metal Organic Framework-Encapsulated Cobalt Nanoparticles. ACS Appl. Mater. Interfaces 2017, 9 (48), 42102-42110. 82.

Zhao, B.; Liu, J.; Guo, X.; Zhao, W.; Liang, L.; Ma, C.; Zhang, R., Hierarchical Porous

Ni@Boehmite/Nickel Aluminum Oxide Flakes with Enhanced Microwave Absorption Ability. Phys. Chem. Chem. Phys. 2017, 19 (13), 9128-9136. 83.

Zhao, B.; Guo, X.; Zhao, W.; Deng, J.; Shao, G.; Fan, B.; Bai, Z.; Zhang, R., Yolk–Shell Ni@SnO2

Composites with a Designable Interspace To Improve the Electromagnetic Wave Absorption Properties. ACS Appl. Mater. Interfaces 2016, 8 (42), 28917-28925. 84.

Liu, T.; Pang, Y.; Zhu, M.; Kobayashi, S., Microporous Co@CoO Nanoparticles with Superior

Microwave Absorption Properties. Nanoscale 2014, 6 (4), 2447-2454. 85.

Yang, J.; Zhang, J.; Liang, C.; Wang, M.; Zhao, P.; Liu, M.; Liu, J.; Che, R., Ultrathin BaTiO3

Nanowires with High Aspect Ratio: A Simple One-Step Hydrothermal Synthesis and Their Strong Microwave Absorption. ACS Appl. Mater. Interfaces 2013, 5 (15), 7146-7151.



Page 26 of 34

Figure 1 Schematic illustration of the fabrication process of (a) PVDF/CNT/Co-chain flexible films and (b) PVDF/CNT/Co-flower flexible films

Figure 2 (a1-a3) SEM images of the as-received Co chains; (b1-b3) SEM image of the asreceived Co flowers; (c1-c2) SEM image and elemental mapping of Co chains; (d1-d2) SEM image and elemental mapping of Co flowers. 26 ACS Paragon Plus Environment

Page 27 of 34 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


Figure 3 XRD patterns of the pure PVDF and the as-received PVDF/CNT/Co(chains or flowers) flexible films.

Figure 4 SEM images of PVDF/CNT/Co composite films with different Co contents: (a) 1 wt% Co chains, (b) 3 wt% Co chains, (c) 6 wt% Co chains, (d) 1 wt% Co flowers, (e) 3wt% Co flowers, (f) 6 wt% Co flowers. 27 ACS Paragon Plus Environment


Page 28 of 34

Figure 5 (a1-a2) SEM image and elemental mapping (Co, C and F) of PVDF/CNT/Co-chain (6 wt%) composite film; (b1-b4) SEM image and elemental mapping (Co, C and F) of PVDF/CNT/Co-flower (6 wt%) composite film.

Figure 6 The electrical conductivity of the as-received PVDF/CNT/Co(chains or flowers) flexible films


Page 29 of 34 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


Figure 7 (a) The variation in measured EMI SE of the as-received PVDF/CNT/Co(chains or flowers) flexible films (0.3 mm) with different Co contents in the range from 18 GHz to 26.5 GHz; (b) The average SE (SET, SEA, and SER) values for the PVDF/CNT/Co(chains or flowers) flexible films of 0.3 mm thickness. Inset in Figure 7b is the percentage (SEA/SET) of each samples.



Page 30 of 34

Figure 8 (a) SET of the PVDF/CNT/Co (6 wt% Co chains) with different thickness in the frequency range of 18.0-26.5 GHz; (b) Average SET, SER and SEA of PVDF/CNT/Co (6 wt% Co chains) with different thickness; (c) SET of the PVDF/CNT/Co (6 wt% Co flowers) with different thickness in the frequency range of 18.0-26.5 GHz; (d) Average SET, SER and SEA of PVDF/CNT/Co (6 wt% Co flowers) with different thickness.


Page 31 of 34 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


Figure 9 Thermal conductivity of the as-received PVDF/CNT/Co(chains or flowers) flexible films



Page 32 of 34

Figure 10 (a) Schematic representation of the thermal properties measured by infrared camera after stopping microwave irradiation; Infrared images of (b1-b4) Co-C-6 and (c1-c4) Co-F-6 samples (0.3 mm thickness) at different time interval after stopping microwave irradiation (1s, 2s, 3s and 4s).


Page 33 of 34 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


Figure 11 Schematic illustration of the microwaves shielding mechanism for (a) the PVDF/CNT/Co-chain and (b) the PVDF/CNT/Co-flower composite flexible films



The PVDF/CNT/Co flexible composite films possessed an absorption-dominated EMI shielding performance as well as high dissipation abilities of heat energy. 107x81mm (600 x 600 DPI)

ACS Paragon Plus Environment

Page 34 of 34

Quick Heat Dissipation in Absorption-Dominated Microwave Shielding

Recommend Documents