aramid nanofibers composite films prepared via a simple filtration method with excellent mechanical and electromagnetic interference shielding properties

Journal Pre-proof 2D Ti3C2Tx MXene/aramid nanofibers composite films prepared via a simple filtration method with excellent mechanical and electromagnetic interference shielding properties Huawei Wei, Mingqiang Wang, Wenhui Zheng, Zaixing Jiang, Yudong Huang PII:

S0272-8842(19)33276-6

DOI:

https://doi.org/10.1016/j.ceramint.2019.11.087

Reference:

CERI 23456

To appear in:

Ceramics International

Received Date: 23 September 2019 Revised Date:

4 November 2019

Accepted Date: 11 November 2019

Please cite this article as: H. Wei, M. Wang, W. Zheng, Z. Jiang, Y. Huang, 2D Ti3C2Tx MXene/ aramid nanofibers composite films prepared via a simple filtration method with excellent mechanical and electromagnetic interference shielding properties, Ceramics International (2019), doi: https:// doi.org/10.1016/j.ceramint.2019.11.087. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.

2D Ti3C2Tx MXene/aramid nanofibers composite films prepared via a simple filtration method with excellent mechanical and electromagnetic interference shielding properties Huawei Wei1, Mingqiang Wang1, Wenhui Zheng1, Zaixing Jiang*,1, Yudong Huang*,1 1

MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and

Storage, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin 150001, China * Corresponding Author, E-mail: [email protected], [email protected]. Keywords: d-Ti3C2Tx, aramid nanofibers, film, electromagnetic interference shielding Abstract Electromagnetic shielding (EMI) materials are becoming more and more important because of the increasingly serious radiation pollution. The preparation of high mechanical strength, ultrathin, lightweight, flexible materials with excellent EMI shielding performance have so far been elusive. Here, we try to prepare a ultrathin, lightweight and flexible film with excellent EMI shielding performance using one-dimensional aramid nanofibers (ANFs) and two-dimensional few-layered Ti3C2Tx through a simple filtration method. The ultimate tensile strength and strain of the film are up to 116.71 MPa and 2.64 %. The EMI shielding effectiveness and the specific EMI shielding efficiency are 34.71 dB and 21971.37 dB cm2 g-1, which will be no recession after 1000 times bending. Our results show that a practical EMI shielding material with excellent

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performances has been successfully prepared, which will be widely applied in wearable electronics, robot joints, and precision instrument protection and so on. 1. Introduction Our modern life is increasingly inseparable from electromagnetic waves, such as wireless communication and our intelligent mobile phone. One of the disadvantages is the electromagnetic (EM) pollution. The EM pollution is harmful for human health and have interfere for the accuracy of electronic equipment [1-4]. Progress in electromagnetic interference (EMI) shielding material preparation has enabled shielding most of EM, but this has been limited to application due to the heavy weight and poor processing [5-9]. We used two-dimensional (2D) Ti3C2Tx MXene and one-dimensional (1D) aramid nanofibers (ANFs) specifically designed to bridge the gap between the EMI shielding performance and suitable for application. Ti3C2Tx MXene (Tx represents surface-terminating functionality -F, =O, -OH), a novel 2D material, is obtained by selectively etching the Al element from ternary transition metal carbides Ti3AlC2 [10]. Due to the large specific surface area and high electrical conductivity, Ti3C2Tx exhibits lightweight and superior EMI shielding performance [2, 11-14]. Faisal Shahzad and coworkers [2] reported flexible Ti3C2Tx and Ti3C2Tx-sodium alginate composite films. The Ti3C2Tx films (thickness 45 µm) and Ti3C2Tx-sodium alginate composite films (90 wt% Ti3C2Tx, thickness 8-9 µm) exhibited excellent EMI shielding effectiveness (SE) of 92 dB and 57 dB, respectively. Ji Liu et al [11] mentioned a hydrophobic, flexible and lightweight MXene foam by a hydrazine-induced foaming process, demonstrating a superior EMI SE of 70 dB (thickness 60 µm). Moreover, a “brick-and-mortar” structure Ti3C2Tx/PEDOT:PSS composite films were prepared by Ruiting Liu et al [15] and exhibited a high EMI SE of 42.1 dB (thickness 11.1 µm).

2

Unfortunately, poor mechanical properties of those materials greatly limited the application in EMI territory. Aramid fiber is a kind of fiber with high mechanical properties, especially Kevlar. Aramid nanofibers (ANFs), derived from Kevlar, are often used as a reinforcement material for composites owing to their high mechanical strength and great flexibility [16-18]. The key benefit of our film is the combination of the Ti3C2Tx EMI performance and ANFs high mechanical properties. Herein, “bricks and cement” structure d-Ti3C2Tx/ANFs composite films are successfully prepared through the distribution of ANFs into d-Ti3C2Tx layers via a vacuum assisted filtration process. In the composite films, d-Ti3C2Tx layers as “brick”, mainly plays a shielding role. ANFs act as “cement” between “d-Ti3C2Tx bricks” to connect and stabilize. The d-Ti3C2Tx/ANFs composite films are expected to have high tensile strength, ultrathin, flexible, excellent EMI shielding performances. Furthermore, the films will be easy to process, and can be made for practical application products. 2. Experimental 2.1 Preparation of 2D structure few-layered d-Ti3C2Tx In general, 4.8 g LiF (99.99%, metals basis, Aladdin Industrial Corporation) and 60 ml 9M HCl (37wt%, Xilong Scientific Co., Ltd) were mixed in teflon beaker and stirring for 10 min to form a homogeneous solution at room temperature. Then, 3 g Ti3AlC2 (98%, 400 mesh, 11 technology Co., Ltd.) powder was carefully added into the mixed solution with magnetic stirring at 600 rpm at 40 ℃ for 24 h. After that, the mixed solution was centrifuged at 3500 rpm several times until the PH of the supernatant was 6. And the obtained black precipitation was collected. Then the precipitation was dispersed in 600 ml deionized water and further subjected to

3

sonication under argon for 45 min. The mixture was then centrifuged at 3500 rpm for 20 min and the supernatant was collected. Subsequently, the supernatant was sonicated for another 15 min under argon atmosphere. Following, the solution was centrifuged at 6000 rpm for 20 min and the supernatant was collected. Finally, though out freeze-drying, the 2D few-layered structure dTi3C2Tx MXene was obtained. 2.2 ANFs dispersion solution (2 mg ml-1) 1 g Kevlar (E.I. Du Pont Company) and 1 g KOH (ACS, Aladdin Industrial Corporation) were added into 500 ml dimethyl sulfoxide (DMSO, 99.7%, safedry, water≤50 ppm, Shanghai Titan Scientific Co., Ltd.) and magnetic stirred for 7 days at ambient environment. After that, a dark red-brown solution was obtained. 2.3 Fabrication of d-Ti3C2Tx/ANFs composite films 20 mg d-Ti3C2Tx was added into 50.00 ml DMSO and ultrasonic dispersion for 1 h. Subsequently, the composite films was conducted by quantitatively adding ANFs solution into the above d-Ti3C2Tx suspension under stirring for 18 h, and the resulting Ti3C2Tx/ANFs mixture was vacuum filtrated (Nylon organic films filter, 0.22µm, 50mm diameter). Then, the asprepared films was immersed in methyl alcohol for 2 days. Finally, the films was obtained by cold pressing at 15 KPa for 24 h at room temperature. The mass ratios between d-Ti3C2Tx and ANFs was 10:1, 8:1, 6:1, 4:1, 2:1 and 1:1. Additionally, the 20 mg d-Ti3C2Tx dispersing in 50.00 ml deionized water, and 10 mg ANFs dispersing in 50.00 ml DMSO and 5.00 ml deionized water was made as films, respectively. 2.4 Characterization

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The structure and morphology of the films were investigated by scanning electron microscope (SEM, Zeiss Sapphire Supra 55, Germany). Transmission electron microscope (TEM, JEM-2100, JEOL, Japan) was used to observe d-Ti3C2Tx and ANFs. The crystal structure was measured by X-ray diffraction patterns (XRD RIGAKU D/MAX-rβ Japan) with Cu Kα radiation (λ = 0.154 nm) over the range of 2θ: 4~90°. Fourier transform infrared (FT-IR) spectroscopy was carried out on a Nicolet Avatar 360 FT-IR spectrometric analyzer (Thermo Fisher Scientific, USA). X-ray photoelectron spectra (XPS, Thermo Fisher Scientific, USA) were obtained in an XPS system, via monochromatic Al Kα radiation with a pass energy of 50eV. Atomic force microscopy (AFM, Dimension Fastscan, Bruker, USA) was employed to test the thickness of the MXene on the silicon wafer. The mechanical properties of the dTi3C2Tx/ANFs composite films were measured by a 5569 universal testing machine (USA). Each sample was cut into a strip of 5 mm×30 mm, and the loading rate was 0.2 mm/min. At least three samples were tested for each measurement to guarantee the accuracy of the data. A vector network analyzer of Agilent N5230A (Agilent Technologies Inc. USA) was applied to obtain the EMI performance. The samples were cut into a rectangle shape with dimensions of 22.9 mm (length) ×10.2 mm (width). The S-parameters, including S11, S12, S22 and S21, of all samples were measured at X-band and EMI SE was calculated from those Sparameters as follows: =

Where

|

|

= 10

|

|

(1)

represented the power transmitted from port I to port j. The total EMI shieling

effectiveness (SET) content SE of reflection (SER), absorption (SEA) and multiple internal

5

reflection (SEM). When SET≥15dB, the SEM can be negligible. Those values were calculated from the S-parameters as follows: =

+

+

≈

= 10 = 10

|

|

|

+

|

|

|

(2)

(3)

(4)

3. Results and Discussion Fig. 1A showed schematic mechanism for preparing d-Ti3C2Tx/ANFs composite film. The d-Ti3C2Tx sheets were delaminating a Ti3AlC2 precursor with LiF/HCl by selectively etching its Al layers (the details were given at Experimental in the paper) [19]. Fig. 1B showed scanning electron microscopy (SEM) images of the products after etching. The bulk Ti3AlC2 (Fig. 1B i and Fig. S1a, according with PDF-#52-0875) changed to clay-like multi-Ti3C2Tx (Fig. 1B ii) [20]. Further processing by ultrasonic and centrifugation, the clay-like m-Ti3C2Tx converted to dTi3C2Tx sheets (Fig. 1B iii). The diffraction peak (0002) shifted to a lower angle and the peak at 2θ = 39° disappeared after delaminating process, which confirmed d-Ti3C2Tx sheets successfully prepared (Fig. S1) [21]. Fig. 1B iiii showed a transmission electron microscopy (TEM) image of ANFs, implying the ANFs ranged from 10 to 20 nm in diameter and a few hundred nanometers in length. The inset was a picture of ANFs suspension. Eventually, d-Ti3C2Tx/ANFs composite film was fabricated via a vacuum assisted filtration (the details were given in Experimental in the paper). Fig. 1C showed the pictures of composite film with diameter of 40~41 mm approximately. Interestingly, the d-Ti3C2Tx/ANFs composite film had excellently flexible

6

property (Fig. S2). The pictures demonstrated there was no destruction of the composite film after continuously folding for four times.

Fig. 1. (A) Schematic illustration of preparation of the d-Ti3C2Tx/ANFs composite films. (B) The morphology for (i) Ti3AlC2, (ii) m-Ti3C2Tx, (iii) d-Ti3C2Tx and (iiii) TEM of ANFs, the inset of dark red-brown solution was the ANFs suspension. (c) Digital picture of the films for (i) ANFs, (ii) d-Ti3C2Tx and (iii) d-Ti3C2Tx/ANFs, the bar represented 10 mm. To further understand the d-Ti3C2Tx, TEM and atomic force microscopy (AFM) was employed. Fig. 2a showed a TEM image of a separated d-Ti3C2Tx sheet. Fig. 2b and c were the elemental mapping of Ti and F of d-Ti3C2Tx, where the Ti signal demonstrated a homogeneous distribution on the surface and F signal showed a random distribution. The AFM images (Fig. 2d and Fig. S3) revealed d-Ti3C2Tx sheets were few-layered structure with a thickness of 1.6~3.6 nm. And the large lateral sized up to several micrometers. Therefore, this unique few-layered

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structure endowed the d-Ti3C2Tx sheets with capability to assemble into flexible functional films [22]. Fig. 2e showed SEM image of d-Ti3C2Tx films with a parallelly, ordered, compact and layered structure, which provided the material with outstanding flexibility (Fig. S2) [15, 23]. After

Fig. 2. (a) The TEM image of d-Ti3C2Tx, and the corresponding elemental mapping of (b) Ti, (c) F. (d) AFM image of the d-Ti3C2Tx sheets deposited on a silicon wafer, the inset curve

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represented the thickness of few-layered Ti3C2Tx along the white dotted line. Cross-section SEM images of (e) pure d-Ti3C2Tx film, d-Ti3C2Tx/ANFs composite film with mass ratio of (f) 10:1, (g) 2:1. (h) XRD patterns of the d-Ti3C2Tx/ANFs composite films. (i) XPS survey spectra of dTi3C2Tx film and d-Ti3C2Tx/ANFs composite film.

assembling with ANFs, the d-Ti3C2Tx/ANFs composite films also exhibited a tightly stacked layered structure (Fig. 2f, g and Fig. S4). And it was obvious that composite film had a “brick and cement” structure with MXene playing a role as “bricks” and ANFs acting as “cement”. When the mass ratio between d-Ti3C2Tx and ANFs was 1:1, the ANFs was enough to form ANFs layers and arranged alternately with MXene layers (Fig. S4d). In addition, the surface morphology of films was also investigated, as shown in Fig. S5 and Fig S6. When the ANFs added, the ANFs could be seen at the surface of film. And with the mass ratio increasing to 6:1, the ANFs would be more at the surface of films. Nevertheless, as the content of ANFs continued to increase to 1:1, ANFs became invisible at the surface, because too much ANFs formed a thin film on the surface of Ti3C2Tx, which was accordance with the structure of the cross-section. Comparison of MXene powder and MXene film, the (0002) peak shifted from 2θ = 6.06°to 6.30° (Fig. S1b), implying the d-Ti3C2Tx film had more compact structure after filtration. Unfortunately, the (0002) peak ranging from 6.40° to 6.24° (Fig. 2h) in composite films, had a little increase with the ANFs increasing, which maybe because of the employed pressure (15KPa) during the preparation of the films. This minor change also indicated the ANFs filled between the MXene sheets [24]. Fig. 2i showed X-ray photoelectron spectroscopy (XPS) patterns of films. The ratio of C/O atomic of the d-Ti3C2Tx /ANFs was higher than that of d-

9

Ti3C2Tx films. The ratio of C/O atomic of the d-Ti3C2Tx /ANFs was higher than that of d-Ti3C2Tx films. Because ANFs contained C, O, N and H, and the C was the most abundant. After ANFs adding, the ratio of C/O atoms increased, implying the ANFs indeed entered into the films. And a new peak of N appeared. In addition, the Fourier transform infrared (FTIR) spectra of the ANFs film was shown in Fig. S7a. The ANFs characteristic absorption bands at 3314.27 (N-H stretching vibrations), 1638.56 (C=O stretching vibrations), 1538.50 (N-H deformation and C-N stretching coupled modes), 1506.81 (C-C stretching vibrations of the aromatic ring) cm-1 were observed in the FTIR spectrum of pure ANFs film [16]. And those characteristic peaks were clearly visible in d-Ti3C2Tx/ANFs composite films (Fig. S7b). The experimental results indicated that the “brick and cement” structure d-Ti3C2Tx/ANFs composite films have been successfully prepared. Fig. 3a and b showed the tensile strength and fracture strains of the d-Ti3C2Tx/ANFs composite films. The contents of d-Ti3C2Tx in the d-Ti3C2Tx/ANFs composite films were estimated by thermogravimetric analysis (TGA), as shown in Fig. S8 and Table S1. Due to the loss of ANFs in filtration process, the ratios by TGA changed slightly with nominal ratios in the experiment. When the ANFs was adding to 10:1, the tensile strength was up to 46.51 ± 4.30 MPa with a fracture strain of 0.94 ± 0.10 %, which was nearly 3 times of pure d-Ti3C2Tx film (16.49 ± 0.78 MPa). The optimal tensile strength was 116.71 MPa and strain at break was 2.64 % when the mass ratio between d-Ti3C2Tx and ANFs was 1:1. The details mechanical properties parameters were exhibited at the table S2. Fig. S9 showed SEM images of the fracture surface, zigzag shapes being seen at the fracture surface. In the beginning, when the stretching started, the layers of MXene would slide over each other because of the poor interconnect for layers. After the ANFs adding, the ANFs filled between d-Ti3C2Tx sheets in the composite film, acting as

10

“cement” between “bricks” to connect and stabilize d-Ti3C2Tx sheets. Thus, ANFs would prevent the slide effect of the layers, which leads to more energy dissipation. Meanwhile, the ANFs molecular chains were stretched to avoid the crack propagation, which would dissipate more energy in the stretching process. This interaction effect between 2D MXene and 1D ANFs resulted that the composite films demonstrated excellent tensile strength. Unfortunately, due to the rigid structure of the ANFs molecular chain and d-Ti3C2Tx, the fracture strain of the composite films improved slightly.

Fig. 3. Mechanical properties and EMI shielding performance of the d-Ti3C2Tx/ANFs composite films. (a) and (b) Tensile strength and strain of d-Ti3C2Tx/ANFs with different mass ratios between d-Ti3C2Tx and ANFs. (c) EMI shielding performance, (d) The average of EMI SET, SER, SEA and (e) SSE/t of the d-Ti3C2Tx/ANFs composite films with different mass ratios between d-Ti3C2Tx and ANFs in X-band. (f) EMI shielding performance of d-Ti3C2Tx/ANFs composite film with mass ratio of 10:1 after 1000 times bending.

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The few-layered d-Ti3C2Tx/ANFs composite films exhibited a superior EMI shielding performance. As shown in the Fig. 3c, the pure MXene films exhibited a maximum EMI shielding effectiveness (SE) of 37.64 dB at 12.4 GHz with the thickness of 11 µm. As for dTi3C2Tx/ANFs composite films, the EMI SE reduced with the content of ANFs increase. A maximum EMI SE of 34.71 dB at 8.2 GHz achieved when the mass ratio was 10:1. Fig. S10a was the EMI shielding performance of pure ANFs, showing a neglectable values of EMI SE. Thus, the EMI shielding was mainly decided by d-Ti3C2Tx content in the composite films. Fig. 3d showed the average of EMI SET, SER, SEA of the d-Ti3C2Tx/ANFs composite films in X-band and exhibiting an absorption-dominant mechanism. The SSE/t (SE divided by sample density and thickness) was used to evaluate the EMI shielding performance of the d-Ti3C2Tx/ANFs composite films. Fig. 3e showed the values of SSE/t of d-Ti3C2Tx/ANFs composite films, and an excellent SSE/t of 21971.37dB cm2 g-1 achieved when the mass ratio was 10:1. The results implied that the ultrathin d-Ti3C2Tx/ANFs composite films not only has excellent mechanical properties but superior EMI shielding performance. More interestingly, the film with the mass ratio of 10:1, suffering 1000 times bending, also had high EMI shielding performance, as shown in Fig. 3f and Fig. S10a and b. The EMI SET had a slight increase, up to 37.78dB at 8.2GHz, showing incredible potential in the application of flexible EMI shielding materials. To explain the excellent EMI shielding properties of d-Ti3C2Tx/ANFs composite films, the proposed EMI shielding mechanism with three stages was illustrated in Fig. 4a. At the beginning, as electromagnetic waves (EW) striking the surface of the MXene/ANFs composite films, owing to the impedance mismatching of MXene/ANFs composite film and the surroundings, some EW was reflected by the film result in reflection energy dissipation [2, 6, 25, 26]. The remaining EW interacted with the d-Ti3C2Tx, which lead to dielectric loss by

12

polarization [12, 15]. Thus, the energy of EW would be absorption. When the surviving EW meet the other d-Ti3C2Tx on the next layer, attenuation phenomenon of the EW repeated. Simultaneously, the ordered lamellar structure in the composite films would cause multiple internal reflections of EW by two adjacent layers acting as reflected surfaces, resulting in further absorbed of the energy of EW [7, 27]. Suffering these reflection and absorption, EW intensity was attenuated effectively. The specific parameter SSE/t was used to compare the EMI shielding performance. So far, the research for EMI shielding has focused on carbon fibers [28, 29], CNTs [30-33], graphene [34-36], and reduced graphene oxide [37, 38], other carbon-based material [39-41], metallicbased

Fig. 4 (a) The proposed EMI shielding mechanism of d-Ti3C2Tx/ANFs composite films. (b) Comparison of the SSE/t with a function of thickness. Each color indicated a set of material

13

category, and the numbers in (b) were sample numbers listed in Table S3. (c) The simple model of d-Ti3C2Tx/ANFs composite films application. material [9, 42, 43], and MXene [2, 6, 11, 12, 15] as shown in Fig. 4b and table S3. This work located at the top left of the diagram, with ultrathin and high EMI shielding performance. Fig. 4c showed a schematic of the tent covered with d-Ti3C2Tx/ANFs films. Assuming that the EW intensity of the surrounding environment was 100%. After the effective of composite films, EW intensity of the tent was less than 0.1%, which prevented a large amount of radiation. The bending property of composite films endowed its reuse many times on tents. The ultrathin and flexible d-Ti3C2Tx/ANFs composite film with excellent mechanical properties and superior EMI shielding performance was highly promising for applications in wearable electronics, robotic joints and precision instrument protection. 4. Conclusions In summary, an ultrathin and flexible d-Ti3C2TxANFs composite films with excellent mechanical properties and superior EMI shielding performance were successfully prepared via a vacuum assisted filtration process. 1D ANFs filled between layers of Ti3C2Tx in the composite film, forming “brick and cement” structure, where MXene sheets acted as “brick” and ANFs acted as “cement” between “bricks” to connect and stabilize. ANFs could dramatically improve the mechanical strength of composite films. The ultimate tensile strength and strain at fracture of the d-Ti3C2Tx/ANFs composite film reached at 116.71 MPa and 2.64%, respectively. Significantly, the composite films exhibited excellent EMI shielding performance. The dTi3C2Tx/ANFs composite film with a thickness of 12 µm had an EMI SE of 34.71 dB at 8.2 GHz. And the SSE/t of composite film was up to 21971.37 dB cm2 g-1. The ultrathin, flexible and high

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mechanical properties d-Ti3C2Tx/ANFs composite films with excellent EMI shielding performance had potential application in various fields such as wearable electronics, robot joints, and precision instrument protection. Acknowledgements The authors acknowledge financial support from National Program for Support of Top-notch Young Professionals, National Natural Science Foundation of China (No. 51773049), China Aerospace Science and Technology Corporation-Harbin Institute of Technology Joint Center for Technology Innovation Fund (HIT15-1A01), Shanghai Academy of Spaceflight Technology Fund (SAST2017-126), Harbin city science and technology projects (2013DB4BP031 and RC2014QN017035), China Postdoctoral Science Special Foundation (No. 201003420, No.20090460067).

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Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☒The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: