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Enhancement of electromagnetic interference shielding effectiveness with alignment of spinnable multiwalled carbon nanotubes
Accepted Manuscript Enhancement of electromagnetic interference shielding effectiveness with alignment of spinnable multiwalled carbon nanotubes Duck Weon Lee, Jongwoo Park, Bum Joon Kim, Hyunsoo Kim, Changsoon Choi, Ray H. Baughman, Seon Jeong Kim PII:
S0008-6223(18)30995-3
DOI:
https://doi.org/10.1016/j.carbon.2018.10.076
Reference:
CARBON 13594
To appear in:
Carbon
Received Date: 27 August 2018 Revised Date:
12 October 2018
Accepted Date: 22 October 2018
Please cite this article as: D.W. Lee, J. Park, B.J. Kim, H. Kim, C. Choi, R.H. Baughman, S.J. Kim, Enhancement of electromagnetic interference shielding effectiveness with alignment of spinnable multiwalled carbon nanotubes, Carbon (2018), doi: https://doi.org/10.1016/j.carbon.2018.10.076. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Enhancement of Electromagnetic Interference Shielding Effectiveness with
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Alignment of Spinnable Multiwalled Carbon Nanotubes
Duck Weon Lee a, Jongwoo Park a, Bum Joon Kim a, Hyunsoo Kim a, Changsoon Choi b, Ray H. Baughman c and Seon Jeong Kim*a
a
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Center for Self-Powered Actuation, Department of Biomedical Engineering, Hanyang University, Seoul 04763, Korea. b
c
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Division of Smart Textile Convergence Research, DGIST, Daegu 42988, South Korea The Alan G. MacDiarmid NanoTech Institute, University of Texas at Dallas, Richardson, TX 75083, USA
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E-mail: [email protected]
Keywords: Spinnable MWNTs, plaid pattern, electromagnetic interference, BaTiO3
Abstract
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This research develops a unique material to shield against electromagnetic interference
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(EMI) by using spinnable multiwalled carbon nanotubes (MWNTs) compoisted with bio-polydimethylsiloxane (PDMS) that contains BaTiO3 (MBPBT). In particular, a plaid pattern, formed from the spinnable MWNTs and containing BaTiO3 and Fe3O4, is very effective in attenuating the propagation of EM waves. The MBPBT composed of the spinnable multilayered MWNTs achieves over 20 dB attenuation at 8.2 - 12.4 GHz (X-band frequency range). This means that a filter type of the spinnable MWNTs is actively able to handle the directionality and movement of unpolarized EMI propagation.
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In addition, the MBPBT is characterized by its strong mechanical advantage (bending
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radius 180°).
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Graphical abstracts
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1. Introduction Due to the sharply increased use of electronic devices, electromagnetic (EM) pollution—which is generated from external sources such as electromagnetic induction
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devices, electrostatic coupling, or conduction—has long caused serious problems.[1-4] In particular, it has a significant influence on the performance of electronic devices, and it may even affect the human body by causing vertigo, nausea, or muscle stimulation.
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To deal with these diverse types of EM pollutions, shielding that uses metal, metal coatings, or metal-plated polymers has been used to date to protect electronic devices.
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Other methods have also been tried to enhance EM-interference (EMI) shielding effectiveness (SE), including core/shell microstructures; porous, multi-walled-carbonnanotube/polymer composites; ordered mesoporous carbon/fused-silica composites; and MXene films.[5-10]
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Although some promising advances in shielding materials have occurred, it is still a huge challenge to produce materials with superb EMI shielding performance. To shield against a propagating EM wave, many of the existing active materials such as
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graphene, magnet particles MWNTs, and single-walled carbon nanotubes (SWNTs)
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have been used in random arrangements. Except for the nematic phase of graphene in a polymer-graphene composite, for almost all active materials the orientation within the substrate material has not been taken into account.[2, 5, 6, 11, 12] Such amorphous arrangements of active materials are not only ineffective at shielding against directional EMI, but also they are not capable of finely attenuating or controlling EMI. Hence, it is necessary to approach shielding against EMI in the sense of actively handling it. Furthermore, from a mechanical point of view, a two-dimensional (2D) film type of
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shielding material such as graphene or MXene has difficulty in retaining its shielding properties at a sharp bending radius at a fold.[7, 10, 13] In here, our EMI shielding study developed a unique EMI shielding material by
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using a plaid pattern of spinnable MWNTs composite with bio-PDMS that contains BaTiO3 (MBPBT) as shown in Figure 1 a). Generally, many ceramic fillers such as BaTiO3 and PbTiO3, which had high dielectric constant, used as a dielectric contributor
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in polymers with graphene, SWNTs, or MWNTs because the dielectric constant (ε) of polymers was generally quite low. This was a reason why this research made use of
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BaTiO3 which was one of the ceramic fillers having high ε.[3] In addition, this research confirmed that the plaid pattern was effective in attenuating EMI by generating a high level of dielectric constant with the ceramic fillers. To build the plaid pattern which was inserted into the MBPBT, this research took advantage of the highly aligned filter
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formed by the spinnable MWNTs, which had a thickness of around 11.1 +/- 2.4 nm. The gaps between the MWNTs in any given layer were about 20 to 30 nm or more, as shown in Figure S1 a) and b). As the spinnable MWNTs was a three dimensional (3D)
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structure, its style was a buckypaper and has aligned nano-size gaps as shown in Figure S1 c), d) and e). The density and areal density of densified spinnable MWNTs were
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typically ~1.5 mg/cm3 and ~3 µg/cm2, respectively. The spinnable MWNTs, placed on both sides of the BPBT, were drawn directly
from a sidewall of a MWCNT forest that had been synthesized by chemical vapor deposition. [14-16] The spinnable MWNTs was pulled in a fixed direction perpendicular to the propagation direction of the EM radiation and then the orientation of the spinnable MWNTs in the 2nd stack could be rotated vertically by changing the direction of the rectangular Teflon plate on which the BPBT film had been placed, as
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shown in Figure 1 b). This means that directional energy of the electrical field in any EM radiation was weakened due to a barrier energy generated by an induced electrical dipole moment in the directionally aligned MWNTs and BaTiO3.[3, 17, 18] Therefore,
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by varying the direction in which the MWNTs are pulled and laid on the Teflon plate (23mm * 10mm), the electric field in the propagating EM radiation can be opposed by that induced in the spinnable MWNTs. As the overall thickness of the layered samples
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was approximately 200 - 250 µm, they were mainly determined by the sprayed amount of the BaTiO3 because a thickness of one MWCNT layer was only 6-16 nm.[13] In
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addition, Fe3O4 also was inserted into the spinnable MWNTS as a supporter to enhance EMI SE because this research expected that it could provide a high value of permeability, which means that it could not only reinforce the dielectric loss but also enhance the magnetic loss in a given frequency region.
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Figure 2 a) shows an SEM image of a cross-sectional area of the multi-layered thin film created from the spinnable MWNTs. Magnetic particles wrapped in a sheet of MWNTs oriented in a single direction are shown in Figure 2 b). A TEM image of a
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plaid pattern fabricated from the spinnable MWNTs is shown in Figure 2 c). Furthermore, the PDMS containing BaTiO3, an active layer consisting of MWNT sheets,
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and magnetic particles is shown in Figure 2 d). Magnetic particles coated by silver nanowires are shown Figure 2 e).
2. Experimental Section 2.1 Materials
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In the acetylene system, carbon multiwall nanotubes (MWNT) forests producing the spinnable MWNTs are grown by the catalytic reaction of acetylene (C2H2, Air Liquide, > 99.6%) with an Fe catalyst in the hot zone of a chemical vapor deposition (CVD)
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furnace (700 °C), with the carrier gases of Ar (750 s.c.c.m.)/H2 (100 s.c.c.m.) flow. By using the e-beam evaporation method, an Fe catalyst layer of 1-3 nm thickness is coated on a silicon wafer as a growth substrate, and then placed on a special quartz holder that
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is capable of injecting and removing the substrate from the hot zone of the CVD furnace.
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Through the above setting, the MWNT forests of ~400 µm length of and outer diameter of ~12 nm (~9 walls) are slowly grown by the mixture gas including C2H2 (50 s.c.c.m.) in 2 to 5 min after preheating for 5 min in the CVD furnace.
2.2 Fabrication of MBPBT
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To fabricate the MBPBT, this research followed the procedure illustrated in Figure 1 c). First, an aqueous ethanol solution of 50 ml, containing an ether-based hydrophilic urethane of 5 wt % (D6, Advance Source Biomaterial Co.), was composited with
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BaTiO3 of 15 wt % (Aldrich®, <100 nm particle) to create a composite BPBT solution.
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The BPBT solution was sprayed on a Teflon plate using an air brush (Yamato Comp Co.). And then pulled the spinnable MWNTs from a MWNT forest and mounted them in parallel on the Teflon plate (1st stack). Another composite material was prepared by mixing 300 mg of Fe3O4 nanopowder (Sigma Aldrich) with 10 ml of a silver nanowire (AgNW) dispersion (Nanopyxis co. Ltd., 1 wt % in ethanol). The Fe3O4/AgNW composite was next sonicated for 1 hour and then deposited on the surface of the spinnable MWNTs as an auxiliary to enhance the conductivity and permeability of the MBPBT.
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Again, 5 ml of the aqueous BPBT was sprayed on the Teflon plate to cover the MWNTs on the Teflon plate and create the 2nd stack. Put the second stack of the spinnable MWNTs either parallel to (ll) or perpendicular to (＋) the MWNTs in the 1st
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stack before the liquid composite material was added. Finally, the BPBT solution was sprayed to cover the second layer of MWNTs and then peeled off the entire MBPBT from the Teflon plate. Through these processes, it was possible to fabricate a
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3. Results and discussion
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multilayered thin-film type of MBPBT with the plaid pattern.
Two types of samples, each containing two stacks of the spinnable MWNTs, were tested by using the measurement system as illustrated in Figure S2. Each stack consisted of two layers of the spinnable MWNTs. For the first sample, which had a multilayered
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plaid pattern of the MWNTs (+) with BPBT, the SE was 10 dB at X-band frequency range (wavelengths 3.75 - 2.40 cm). For the second sample, which contained a
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multilayered parallel pattern of MWNTs (Ⅱ) implanted into BPBT, the SE was about 2 dB. By manipulating relative orientations of the 1st stack (2 layers) and the 2nd stack (2
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layers), each of which was less than 50 to 60 nm thick, a significant difference of about 8 dB occurred in EMI SE. This showed that the relative orientation of the two stacks, consisting of only four spinnable MWNT layers (about 100 - 120 nm thickness), could be quite effective in attenuating and controlling EMI, as shown in Figure 3 a). In addition, by analyzing the SE of 10 dB produced from the first sample (+), about 2 dB of the attenuation was due to reflection and that 8 dB was due to absorption, as illustrated in Figure 3 b). That is, most of the EMI was absorbed by the spinnable
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MWNTs, thus minimizing any damage caused by secondary reflections of the EMI. In particular, the effectiveness of the MBPBT filter in absorbing EMI was closely related
interaction between the external electric field and the MBPBT.
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to the induction of electric and magnetic dipole moments that originate from the
Absorption by the substrate itself which consists only of PDMS containing BaTiO3 (0.052g) was not significant, because its EMI SE was only 0.1 dB, as shown in
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Figure S3 a). However, this substrate had a large dielectric constant, which acted to increase the SE of the spinnable MWNTs on both sides, even though the composite
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material of PDMS containing BaTiO3 did not have a large shielding effectiveness on its own. In addition, the mechanical strength of this substrate was very weak, with a tensile strength of only 0.09 MPa at a strain of 1.6 %. In contrast, a tensile strength of the BaTiO3 with the four-layered plaid pattern of MWNTs (+) was 2.6 MPa at a strain of
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25 %. Thus, the tensile strength of the MBPBT was reinforced up to 2,800 %, and the strain was also increased by 1,500 % (Shimadzu Co. EZ-SX 10N), as shown in Figure S3 b). This was the reason for strengthening the spinnable MWNTs and the PDMS
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matrix by interfacial bonding with a high aspect ratio of MWNTs. The alignment of the MWNTs apparently resulted in enhancement of the stress and strain by transfer between
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the MWNTs and the PDMS matrix containing BaTiO3 (15 wt %).[3, 19, 20] By analyzing MBPBT this research developed, it demonstrated a meaningful
difference in the dielectric constant ε, depending on the orientation of the spinnable MWNTs. The real part of dielectric constant for the plaid pattern of two stacks of spinnable MWNTs was relatively high, about 228.8 to 81.0, but it declined sharply with increasing frequency in the X-band frequency range. Although its imaginary part was higher than that of the real part, it was also rapidly sunk on increase. In addition, the
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real part of dielectric constant in the parallel pattern of spinnable MWNTs had a relatively low dielectric constant from 41.8 to 19.6, but its imaginary part was lower than that of the real part as shown in Figure 3 c). Moreover, the dielectric properties of
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plaid pattern of MBPBT was more sensitive to the frequency range than those of the parallel pattern of MBPBT.
The reason for the decline in the dielectric constant was the decreasing ability
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of the dipoles to keep up with the rapidly vibrating electric vector as the frequency of the incident EM radiation increased. This demonstrated that the dielectric constant of
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these materials was significantly affected by the alignment of the spinnable MWNTs because the plaid pattern disturbed the propagation and the sinusoidal variation of the EMI wave. Hence, in a condition of Figure 1 a), this was due to the amounts of dipole polarization, that could be induced when the EMI passing through the first spinnable
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MWNTs met the next spinnable MWNTS in the different direction, were relatively increase. Simultaneously, the large network of millions of capacitors, that were formed by the spinnable MWNTs and BaTiO3, possessed a superior dielectric constant.[3, 21-
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24] When an EM wave passed through the MBPBT filter, energy consumed was high, and consequently EMI attenuation was relatively large. Conversely, when the EM wave
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was parallelly met with the spinnable MWNTs, the number of dipole polarization that were induced relatively small, and the value of dielectric constant was small. Therefore, the smaller the value of the dielectric constant, the smaller the electrical polarization provided by the combination of MWNTs and BPBT in an applied electrical field. Furthermore, the dielectric properties depend on the microstructure of MBPBT. In particular, dielectric constant in this research was strongly related to two mechanisms; The first one was the interfacial polarization effect (Maxwell-Wagner-Sillars) which
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was caused by stack of many charge carriers at the internal interfaces between the spinnable MWNTs and PDMS including BaTiO3. As the other one was the nanocapacitance structure model, it assumed that many parallel nano-capacitors were
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linearly connected with each other in a polymer builder. Based on the both mechanism, a level of dielectric constant, loss, and frequency in the interfacial polarization effect were generally higher than those of the nano-capacitance structure due to a formation of
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the spinnable MWNTs in MBPBT.[25-26] In this research, a structure of the plaid pattern was close to the interfacial polarization effect model, while that of the parallel
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pattern was similar to the nano-capacitance structure model. Therefore, the vertically vibrated EM wave meets the MWNTs lying parallel, which induced more reactions between EM wave and the MWNTs, which means that many charge carriers could be more induced at the internal interfaces between PDMS including BaTiO3 and MWNTs
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as shown in Figure 1 a). This research assumed that the higher dielectric constant could be lead from such reactions in the MBPBT having a plaid pattern of the spinnable MWNTs
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The permeability µ of each sample remained between 0 and 2. For the plaid pattern of the two stacks of the spinnable MWNTs, the real part of the permeability was
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very strong between 9 and 10 GHz, whereas for its real part of the parallel pattern, the interaction between the Fe3O4 and the EMI produced a relatively stable permeability of about 0.8. Both permeability fluctuated at X-band frequency range, with the fluctuations for the plaid pattern of multilayered MWNTs being particularly strong as shown in Figure 3 d). However, the imaginary parts of the plaid and parallel pattern were converged to about ‘0’ in accordance with increase of the frequency even though volatility of the imaginary of the plaid pattern was larger than that of the parallel pattern.
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This means that EMI interacted particularly strongly with the magnetic particles deposited on the layer of spinnable MWNTs, depending upon the direction in which the spinnable MWNTs had been laid out. [27-29]
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The plaid pattern, built from two stacks that include only four layers of spinnable MWNTs with BPBT, was able to attenuate EMI by about 10 dB, but the EMI SE could be further increased with a multiply layered system. Consequently, this
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research investigated this by using 2 (2 + 2), 5 (5 + 5), 10 (10 + 10), 20 (20 + 20), or 40 (40 + 40) layers per stack and then found that, as the number of spinnable MWNT
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layers placed on both sides of the BPBT was increased, the EMI SE increased sharply, but the rate of increase slowly declined after 20 layers per stack, resembling a parabolic curve. In particular, EMI SE exceeded the commercial reference value of 20 dB by using 40 layers of MWNTs in both the 1st stack and the 2nd stack (40 + 40). This
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demonstrated that SE could be increased indefinitely by controlling carefully the number of spinnable MWNT layers, as shown in Figure 4 a). On the contrary, the power transmittance (%) decreased sharply as shown in Figure S4. Moreover, although EMI
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SE of the spinnable MWCNT layers was related to absorption and reflection, simultaneously, its major mechanism was absorption. To more clearly demonstrate it,
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40 (40 + 40), 20 (20 + 20), and 10 (10 + 10) layers of the spinnable MWCNT per stack without having any other materials were tested as shown in Figure S5. This research recognized that attenuation of EMI SE was mainly performed by the spinnable MWNTs. In particular, it was very efficient to absorb EM wave rather than to reflect it. More than 95 % of EM waves are absorbed in total SE. From these results, this research demonstrated that SE can be enhanced by controlling the directionality of the spinnable MWNTs. As the MWNTs were rotated
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helically by 45°and 135°relative to the vertical direction for the same number of layers and BPBT condition, the SE increased by about 1 - 2 dB, as shown in Figure 4 b). Based on these results, for a filter consisting of two layers of spinnable MWNTs, both
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oriented in the same direction, the SE was only 9 dB (Ⅱ). This was raised to about 18 dB when the two layers were oriented in perpendicular directions (＋), and the SE
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increased further, up to approximately 20 dB, for five layers oriented in in four directions ( ). In other words, depending on how the spinnable MWNT layers are
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oriented, the resulting SE varied significantly. This means that this composite material was very effective for EMI shielding.
Moreover, SE of MBPBT was closely related to its specific electrical resistance. Figure 4 c) demonstrated the volume resistance in the horizontal direction for both samples decreased as SE increased. However, the rates of decrease in the specific
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ρ(ohm-cm) = Rtd / l,
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electrical resistance (ρ) were quite different. These values were calculated from
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where R is the linear resistance, t is the thickness of the material, d is the depth, and l is the width. The specific volume resistance for the plaid pattern of multi-layered MWNTs was found to be relatively high, but the value decreased from 6.73*10−3 (Ω-cm: 5 + 5 layers) to 9.70*10−4 (Ω-cm: 40 + 40 layers) as the number of layers of MWNTs increased. On the other hand, for the parallel pattern of multi-layered MWNTs, the measured value was relatively low, decreasing slightly from 4.03*10−4 (Ω-cm: 10 layers) to 1.20*10−4 (Ω-cm: 80 layers). Hence, this research confirmed that the alignment
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direction of the MWNTs caused a big difference in the specific volume resistance, and the shielding effect was maximized when the resistance was the lowest as the number of MWNTs increased.
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Furthermore, the Simon formula showed that this relationship depended strongly on the conductivity, which was the reason the silver nanowires were added;[7, 10, 30, 31]
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EMI shielding effectiveness (SE) = 50 + 10 log (σ/f ) + 1.7t
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Here, σ is the electrical conductivity, f is the frequency, and t is the thickness of the shielding material. Figure S6 a) showed conductivity in the parallel and plaid pattern of 5, 10, 20 and 40 multilayered MWNTs per stack based on the parallel measurement direction. Based on the measurement direction, conductivity was measured in the
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parallel pattern of 5, 10, 20 and 40 multilayered MWNTs per stack under two probe system as shown in Figure S6 b). In the parallel pattern of the 5, 10, 20 and 40 multilayered MWNTs per stack, the first 5, 10, 20, and 40 layers and the remained 5, 10,
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20 and 40 layers were also the same direction, which created many ways where
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electrons were easily able to move in the distance. On the other hand, the direction of the first layers and the remained layers were different, which means that the ways where electrons move relatively decreased in the plaid pattern of multi-layered MWNTs, which caused that conductivity was also decreased. However, EMI shielding effectiveness of the plaid pattern of the multilayerd MWNTs was high that the plaid pattern of multilayered MWNTs considered a movement property of the EM wave. This means that an incident EM wave was easily able to be admitted or transmitted in only one direction when the direction of the spinnable MWNTs was parallel to the oscillating
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direction of the EM, while the EM waves that flow only in one direction react with the vertically placed spinnable MWNTs and then were largely reflected or absorbed as shown in Figure 1 a). From the results, conductivity in the parallel pattern of the
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spinnable MWNTs was higher than that in any other cases when it was measured by the parallel measurement direction. Also, increase of the number of the spinnable MWNTs enhanced conductivity and EMI SE, which was correspondent with the Simon formula.
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However, the result regarding the relationship between EMI SE and conductivity was not matched with the formula when the spinnable MWNTs was highly aligned.
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Magnetic particles wrapped with the silver nanowires interacted with the EMI, even though this was not a significant effect for enhancing SE, as illustrated in Figure 4 d). The samples with and without magnetic particles were compared while increasing the number of MWNTs (2 + 2, 5 + 5, 10 + 10, 20 + 20, 40 + 40 layers), as shown in
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Figure 4 d). When the number of layers was small, we obtained a difference of 4 dB for 2 (2 + 2) and 5 (5 + 5) layers. On the other hand, the difference was only about 0.6 dB for 10 (10 + 10) or more layers, as shown in Figure 4 d). This shows that the magnetic
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permeability plays a large role when the number of layers of MWNTs is small, but the magnetic particles did not have much effect for larger numbers of layers.[1]
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Furthermore, the results were related to interfacial polarization, which was affected by stronger coupling at a gap among Fe3O4 and a heterogenous condition between the spinnable MWNTs and Fe3O4. However, the Fe3O4 could lead a decrease of conductivity, which resulted in a decrease of permittivity because efficiency of dipoles decreased through alternation of electrical vector of incident EM radiation. Hence, to increase the conductivity, the silver nanowire was inserted with Fe3O4.
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In addition, because the MBPBT was also very flexible, there was no problem in bending it through 180° without compromising its performance beyond the bending radius of existing graphene materials or MXene. This was due to the continuous,
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reticulated architecture of the spinnable MWNTs with BPBT.[20] Figure 5 a) showed the dielectric constant of another sample, which was measured again after bending it through 180°, and the values in the dielectric constants were almost identical. This was
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better than for any other film type of EMI shielding material. By utilizing this flexibility, it would be possible to apply this new composite material to many small electronic
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devices, such as portable and wearable smart devices and military equipment. To illustrate this, Figure 5 b) showed that MBPBT could be attached as a hinge of a small
4. Conclusions
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box.
In conclusion, this research demonstrated that the EMI SE was maximized by using a plaid pattern of spinnable MWNTs at X-band frequency range. Hence, we achieved
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commercial-grade shielding effect (over 20 dB) for any electronic devices. Also, the
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value in EMI shielding effectiveness was ultimately determined by the direction and number of layers of MWNTs. This means that a filter type of the spinnable MWNTs was actively able to handle the directionality and movement of unpolarized EMI propagation. Furthermore, we also confirmed that the dielectric constant of MBPBT was relatively high because of the interactions between the BPBT and the spinnable MWNTs when external electromagnetic radiation was applied. This verified that the disparity between two adjacent spinnable MWNTs with BPBT caused electrical charge accumulation and polarization on the surfaces of the MWNTs. Moreover, the MBPBT
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was characterized by its strong mechanical advantage (bending radius 180°) and excellent adhesiveness due to the characteristics of PDMS.
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Acknowledgments
This work was supported in Korea by the Creative Research Initiative Center for SelfPowered Actuation, the Korea-US Air Force Cooperation Program (Grant No.
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2013K1A3A1A32035592), and the National Research Foundation (Grant No. 2016R1C1B2012340) of the Ministry of Science, ICT & Future Planning (MSIP). The
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spinnable MWNTs were provided by LINTEC of America, INC.
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151–160.
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Figure 1. a) Schematic of a plaid pattern formed by spinnable MWNTs with BaTiO3, b) Illustration of the fabrication of a plaid pattern of spinnable MWNTs on a Teflon plate,
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Fe3O4/AgNW.
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c) fabrication processes of the MBPBT containing BPBT and composite of
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Figure 2. SEM images of a) multi-layered cross-sectional view of the EMI shielding material, b) magnetic particles wrapped by aligned MWNT sheets, c) TEM image of a plaid pattern fabricated from the spinnable MWNTs (2+2), SEM images of d) the
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PDMS containing BaTiO3, e) magnetic particles coated by silver nanowires.
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Figure 3. a) Comparison of EMI shielding efficiency of MBPBTs having perpendicular and parallel alignments of MWNTs (2 + 2 vs 2 ll 2), b) analysis of the shielding
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efficiency consisting of both absorption and reflection, c) dielectric constant of MBPBT having a perpendicular and a parallel alignment of MWNTs, d) permeability of MBPBT
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having a perpendicular and a parallel alignment of MWNTs, at X-band frequency range (8.2-12.4 GHz).
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Figure 4. a) The EMI SE for 2 (2 + 2), 5 (5 + 5), 10 (10 + 10), 20 (20 + 20), and 40 (40 + 40) layers of MWNTs with MBPBT. b) Comparison of the EMI SE based on the
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orientations of the spinnable MWNTs (20 + 20 vs 20 ll 20), c) Change in the specific volume resistance for the parallel and plaid patterns of multilayered MWNTs. d)
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Comparison of the EMI SE of MBPBT with and without magnetic particles and silver nanowires.
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Figure 5. a) Change in real part of dielectric constant before and after bending the sample. b) Optical images illustrating the mechanical property of MBPBT wrapped
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around as a hinge of a small box.
S0008-6223(18)30995-3
DOI:
https://doi.org/10.1016/j.carbon.2018.10.076
Reference:
CARBON 13594
To appear in:
Carbon
Received Date: 27 August 2018 Revised Date:
12 October 2018
Accepted Date: 22 October 2018
Please cite this article as: D.W. Lee, J. Park, B.J. Kim, H. Kim, C. Choi, R.H. Baughman, S.J. Kim, Enhancement of electromagnetic interference shielding effectiveness with alignment of spinnable multiwalled carbon nanotubes, Carbon (2018), doi: https://doi.org/10.1016/j.carbon.2018.10.076. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Enhancement of Electromagnetic Interference Shielding Effectiveness with
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Alignment of Spinnable Multiwalled Carbon Nanotubes
Duck Weon Lee a, Jongwoo Park a, Bum Joon Kim a, Hyunsoo Kim a, Changsoon Choi b, Ray H. Baughman c and Seon Jeong Kim*a
a
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Center for Self-Powered Actuation, Department of Biomedical Engineering, Hanyang University, Seoul 04763, Korea. b
c
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Division of Smart Textile Convergence Research, DGIST, Daegu 42988, South Korea The Alan G. MacDiarmid NanoTech Institute, University of Texas at Dallas, Richardson, TX 75083, USA
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E-mail: [email protected]
Keywords: Spinnable MWNTs, plaid pattern, electromagnetic interference, BaTiO3
Abstract
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This research develops a unique material to shield against electromagnetic interference
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(EMI) by using spinnable multiwalled carbon nanotubes (MWNTs) compoisted with bio-polydimethylsiloxane (PDMS) that contains BaTiO3 (MBPBT). In particular, a plaid pattern, formed from the spinnable MWNTs and containing BaTiO3 and Fe3O4, is very effective in attenuating the propagation of EM waves. The MBPBT composed of the spinnable multilayered MWNTs achieves over 20 dB attenuation at 8.2 - 12.4 GHz (X-band frequency range). This means that a filter type of the spinnable MWNTs is actively able to handle the directionality and movement of unpolarized EMI propagation.
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In addition, the MBPBT is characterized by its strong mechanical advantage (bending
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radius 180°).
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Graphical abstracts
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1. Introduction Due to the sharply increased use of electronic devices, electromagnetic (EM) pollution—which is generated from external sources such as electromagnetic induction
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devices, electrostatic coupling, or conduction—has long caused serious problems.[1-4] In particular, it has a significant influence on the performance of electronic devices, and it may even affect the human body by causing vertigo, nausea, or muscle stimulation.
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To deal with these diverse types of EM pollutions, shielding that uses metal, metal coatings, or metal-plated polymers has been used to date to protect electronic devices.
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Other methods have also been tried to enhance EM-interference (EMI) shielding effectiveness (SE), including core/shell microstructures; porous, multi-walled-carbonnanotube/polymer composites; ordered mesoporous carbon/fused-silica composites; and MXene films.[5-10]
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Although some promising advances in shielding materials have occurred, it is still a huge challenge to produce materials with superb EMI shielding performance. To shield against a propagating EM wave, many of the existing active materials such as
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graphene, magnet particles MWNTs, and single-walled carbon nanotubes (SWNTs)
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have been used in random arrangements. Except for the nematic phase of graphene in a polymer-graphene composite, for almost all active materials the orientation within the substrate material has not been taken into account.[2, 5, 6, 11, 12] Such amorphous arrangements of active materials are not only ineffective at shielding against directional EMI, but also they are not capable of finely attenuating or controlling EMI. Hence, it is necessary to approach shielding against EMI in the sense of actively handling it. Furthermore, from a mechanical point of view, a two-dimensional (2D) film type of
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shielding material such as graphene or MXene has difficulty in retaining its shielding properties at a sharp bending radius at a fold.[7, 10, 13] In here, our EMI shielding study developed a unique EMI shielding material by
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using a plaid pattern of spinnable MWNTs composite with bio-PDMS that contains BaTiO3 (MBPBT) as shown in Figure 1 a). Generally, many ceramic fillers such as BaTiO3 and PbTiO3, which had high dielectric constant, used as a dielectric contributor
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in polymers with graphene, SWNTs, or MWNTs because the dielectric constant (ε) of polymers was generally quite low. This was a reason why this research made use of
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BaTiO3 which was one of the ceramic fillers having high ε.[3] In addition, this research confirmed that the plaid pattern was effective in attenuating EMI by generating a high level of dielectric constant with the ceramic fillers. To build the plaid pattern which was inserted into the MBPBT, this research took advantage of the highly aligned filter
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formed by the spinnable MWNTs, which had a thickness of around 11.1 +/- 2.4 nm. The gaps between the MWNTs in any given layer were about 20 to 30 nm or more, as shown in Figure S1 a) and b). As the spinnable MWNTs was a three dimensional (3D)
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structure, its style was a buckypaper and has aligned nano-size gaps as shown in Figure S1 c), d) and e). The density and areal density of densified spinnable MWNTs were
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typically ~1.5 mg/cm3 and ~3 µg/cm2, respectively. The spinnable MWNTs, placed on both sides of the BPBT, were drawn directly
from a sidewall of a MWCNT forest that had been synthesized by chemical vapor deposition. [14-16] The spinnable MWNTs was pulled in a fixed direction perpendicular to the propagation direction of the EM radiation and then the orientation of the spinnable MWNTs in the 2nd stack could be rotated vertically by changing the direction of the rectangular Teflon plate on which the BPBT film had been placed, as
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shown in Figure 1 b). This means that directional energy of the electrical field in any EM radiation was weakened due to a barrier energy generated by an induced electrical dipole moment in the directionally aligned MWNTs and BaTiO3.[3, 17, 18] Therefore,
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by varying the direction in which the MWNTs are pulled and laid on the Teflon plate (23mm * 10mm), the electric field in the propagating EM radiation can be opposed by that induced in the spinnable MWNTs. As the overall thickness of the layered samples
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was approximately 200 - 250 µm, they were mainly determined by the sprayed amount of the BaTiO3 because a thickness of one MWCNT layer was only 6-16 nm.[13] In
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addition, Fe3O4 also was inserted into the spinnable MWNTS as a supporter to enhance EMI SE because this research expected that it could provide a high value of permeability, which means that it could not only reinforce the dielectric loss but also enhance the magnetic loss in a given frequency region.
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Figure 2 a) shows an SEM image of a cross-sectional area of the multi-layered thin film created from the spinnable MWNTs. Magnetic particles wrapped in a sheet of MWNTs oriented in a single direction are shown in Figure 2 b). A TEM image of a
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plaid pattern fabricated from the spinnable MWNTs is shown in Figure 2 c). Furthermore, the PDMS containing BaTiO3, an active layer consisting of MWNT sheets,
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and magnetic particles is shown in Figure 2 d). Magnetic particles coated by silver nanowires are shown Figure 2 e).
2. Experimental Section 2.1 Materials
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In the acetylene system, carbon multiwall nanotubes (MWNT) forests producing the spinnable MWNTs are grown by the catalytic reaction of acetylene (C2H2, Air Liquide, > 99.6%) with an Fe catalyst in the hot zone of a chemical vapor deposition (CVD)
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furnace (700 °C), with the carrier gases of Ar (750 s.c.c.m.)/H2 (100 s.c.c.m.) flow. By using the e-beam evaporation method, an Fe catalyst layer of 1-3 nm thickness is coated on a silicon wafer as a growth substrate, and then placed on a special quartz holder that
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is capable of injecting and removing the substrate from the hot zone of the CVD furnace.
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Through the above setting, the MWNT forests of ~400 µm length of and outer diameter of ~12 nm (~9 walls) are slowly grown by the mixture gas including C2H2 (50 s.c.c.m.) in 2 to 5 min after preheating for 5 min in the CVD furnace.
2.2 Fabrication of MBPBT
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To fabricate the MBPBT, this research followed the procedure illustrated in Figure 1 c). First, an aqueous ethanol solution of 50 ml, containing an ether-based hydrophilic urethane of 5 wt % (D6, Advance Source Biomaterial Co.), was composited with
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BaTiO3 of 15 wt % (Aldrich®, <100 nm particle) to create a composite BPBT solution.
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The BPBT solution was sprayed on a Teflon plate using an air brush (Yamato Comp Co.). And then pulled the spinnable MWNTs from a MWNT forest and mounted them in parallel on the Teflon plate (1st stack). Another composite material was prepared by mixing 300 mg of Fe3O4 nanopowder (Sigma Aldrich) with 10 ml of a silver nanowire (AgNW) dispersion (Nanopyxis co. Ltd., 1 wt % in ethanol). The Fe3O4/AgNW composite was next sonicated for 1 hour and then deposited on the surface of the spinnable MWNTs as an auxiliary to enhance the conductivity and permeability of the MBPBT.
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Again, 5 ml of the aqueous BPBT was sprayed on the Teflon plate to cover the MWNTs on the Teflon plate and create the 2nd stack. Put the second stack of the spinnable MWNTs either parallel to (ll) or perpendicular to (＋) the MWNTs in the 1st
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stack before the liquid composite material was added. Finally, the BPBT solution was sprayed to cover the second layer of MWNTs and then peeled off the entire MBPBT from the Teflon plate. Through these processes, it was possible to fabricate a
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3. Results and discussion
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multilayered thin-film type of MBPBT with the plaid pattern.
Two types of samples, each containing two stacks of the spinnable MWNTs, were tested by using the measurement system as illustrated in Figure S2. Each stack consisted of two layers of the spinnable MWNTs. For the first sample, which had a multilayered
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plaid pattern of the MWNTs (+) with BPBT, the SE was 10 dB at X-band frequency range (wavelengths 3.75 - 2.40 cm). For the second sample, which contained a
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multilayered parallel pattern of MWNTs (Ⅱ) implanted into BPBT, the SE was about 2 dB. By manipulating relative orientations of the 1st stack (2 layers) and the 2nd stack (2
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layers), each of which was less than 50 to 60 nm thick, a significant difference of about 8 dB occurred in EMI SE. This showed that the relative orientation of the two stacks, consisting of only four spinnable MWNT layers (about 100 - 120 nm thickness), could be quite effective in attenuating and controlling EMI, as shown in Figure 3 a). In addition, by analyzing the SE of 10 dB produced from the first sample (+), about 2 dB of the attenuation was due to reflection and that 8 dB was due to absorption, as illustrated in Figure 3 b). That is, most of the EMI was absorbed by the spinnable
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MWNTs, thus minimizing any damage caused by secondary reflections of the EMI. In particular, the effectiveness of the MBPBT filter in absorbing EMI was closely related
interaction between the external electric field and the MBPBT.
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to the induction of electric and magnetic dipole moments that originate from the
Absorption by the substrate itself which consists only of PDMS containing BaTiO3 (0.052g) was not significant, because its EMI SE was only 0.1 dB, as shown in
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Figure S3 a). However, this substrate had a large dielectric constant, which acted to increase the SE of the spinnable MWNTs on both sides, even though the composite
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material of PDMS containing BaTiO3 did not have a large shielding effectiveness on its own. In addition, the mechanical strength of this substrate was very weak, with a tensile strength of only 0.09 MPa at a strain of 1.6 %. In contrast, a tensile strength of the BaTiO3 with the four-layered plaid pattern of MWNTs (+) was 2.6 MPa at a strain of
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25 %. Thus, the tensile strength of the MBPBT was reinforced up to 2,800 %, and the strain was also increased by 1,500 % (Shimadzu Co. EZ-SX 10N), as shown in Figure S3 b). This was the reason for strengthening the spinnable MWNTs and the PDMS
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matrix by interfacial bonding with a high aspect ratio of MWNTs. The alignment of the MWNTs apparently resulted in enhancement of the stress and strain by transfer between
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the MWNTs and the PDMS matrix containing BaTiO3 (15 wt %).[3, 19, 20] By analyzing MBPBT this research developed, it demonstrated a meaningful
difference in the dielectric constant ε, depending on the orientation of the spinnable MWNTs. The real part of dielectric constant for the plaid pattern of two stacks of spinnable MWNTs was relatively high, about 228.8 to 81.0, but it declined sharply with increasing frequency in the X-band frequency range. Although its imaginary part was higher than that of the real part, it was also rapidly sunk on increase. In addition, the
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real part of dielectric constant in the parallel pattern of spinnable MWNTs had a relatively low dielectric constant from 41.8 to 19.6, but its imaginary part was lower than that of the real part as shown in Figure 3 c). Moreover, the dielectric properties of
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plaid pattern of MBPBT was more sensitive to the frequency range than those of the parallel pattern of MBPBT.
The reason for the decline in the dielectric constant was the decreasing ability
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of the dipoles to keep up with the rapidly vibrating electric vector as the frequency of the incident EM radiation increased. This demonstrated that the dielectric constant of
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these materials was significantly affected by the alignment of the spinnable MWNTs because the plaid pattern disturbed the propagation and the sinusoidal variation of the EMI wave. Hence, in a condition of Figure 1 a), this was due to the amounts of dipole polarization, that could be induced when the EMI passing through the first spinnable
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MWNTs met the next spinnable MWNTS in the different direction, were relatively increase. Simultaneously, the large network of millions of capacitors, that were formed by the spinnable MWNTs and BaTiO3, possessed a superior dielectric constant.[3, 21-
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24] When an EM wave passed through the MBPBT filter, energy consumed was high, and consequently EMI attenuation was relatively large. Conversely, when the EM wave
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was parallelly met with the spinnable MWNTs, the number of dipole polarization that were induced relatively small, and the value of dielectric constant was small. Therefore, the smaller the value of the dielectric constant, the smaller the electrical polarization provided by the combination of MWNTs and BPBT in an applied electrical field. Furthermore, the dielectric properties depend on the microstructure of MBPBT. In particular, dielectric constant in this research was strongly related to two mechanisms; The first one was the interfacial polarization effect (Maxwell-Wagner-Sillars) which
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was caused by stack of many charge carriers at the internal interfaces between the spinnable MWNTs and PDMS including BaTiO3. As the other one was the nanocapacitance structure model, it assumed that many parallel nano-capacitors were
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linearly connected with each other in a polymer builder. Based on the both mechanism, a level of dielectric constant, loss, and frequency in the interfacial polarization effect were generally higher than those of the nano-capacitance structure due to a formation of
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the spinnable MWNTs in MBPBT.[25-26] In this research, a structure of the plaid pattern was close to the interfacial polarization effect model, while that of the parallel
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pattern was similar to the nano-capacitance structure model. Therefore, the vertically vibrated EM wave meets the MWNTs lying parallel, which induced more reactions between EM wave and the MWNTs, which means that many charge carriers could be more induced at the internal interfaces between PDMS including BaTiO3 and MWNTs
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as shown in Figure 1 a). This research assumed that the higher dielectric constant could be lead from such reactions in the MBPBT having a plaid pattern of the spinnable MWNTs
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The permeability µ of each sample remained between 0 and 2. For the plaid pattern of the two stacks of the spinnable MWNTs, the real part of the permeability was
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very strong between 9 and 10 GHz, whereas for its real part of the parallel pattern, the interaction between the Fe3O4 and the EMI produced a relatively stable permeability of about 0.8. Both permeability fluctuated at X-band frequency range, with the fluctuations for the plaid pattern of multilayered MWNTs being particularly strong as shown in Figure 3 d). However, the imaginary parts of the plaid and parallel pattern were converged to about ‘0’ in accordance with increase of the frequency even though volatility of the imaginary of the plaid pattern was larger than that of the parallel pattern.
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This means that EMI interacted particularly strongly with the magnetic particles deposited on the layer of spinnable MWNTs, depending upon the direction in which the spinnable MWNTs had been laid out. [27-29]
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The plaid pattern, built from two stacks that include only four layers of spinnable MWNTs with BPBT, was able to attenuate EMI by about 10 dB, but the EMI SE could be further increased with a multiply layered system. Consequently, this
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research investigated this by using 2 (2 + 2), 5 (5 + 5), 10 (10 + 10), 20 (20 + 20), or 40 (40 + 40) layers per stack and then found that, as the number of spinnable MWNT
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layers placed on both sides of the BPBT was increased, the EMI SE increased sharply, but the rate of increase slowly declined after 20 layers per stack, resembling a parabolic curve. In particular, EMI SE exceeded the commercial reference value of 20 dB by using 40 layers of MWNTs in both the 1st stack and the 2nd stack (40 + 40). This
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demonstrated that SE could be increased indefinitely by controlling carefully the number of spinnable MWNT layers, as shown in Figure 4 a). On the contrary, the power transmittance (%) decreased sharply as shown in Figure S4. Moreover, although EMI
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SE of the spinnable MWCNT layers was related to absorption and reflection, simultaneously, its major mechanism was absorption. To more clearly demonstrate it,
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40 (40 + 40), 20 (20 + 20), and 10 (10 + 10) layers of the spinnable MWCNT per stack without having any other materials were tested as shown in Figure S5. This research recognized that attenuation of EMI SE was mainly performed by the spinnable MWNTs. In particular, it was very efficient to absorb EM wave rather than to reflect it. More than 95 % of EM waves are absorbed in total SE. From these results, this research demonstrated that SE can be enhanced by controlling the directionality of the spinnable MWNTs. As the MWNTs were rotated
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helically by 45°and 135°relative to the vertical direction for the same number of layers and BPBT condition, the SE increased by about 1 - 2 dB, as shown in Figure 4 b). Based on these results, for a filter consisting of two layers of spinnable MWNTs, both
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oriented in the same direction, the SE was only 9 dB (Ⅱ). This was raised to about 18 dB when the two layers were oriented in perpendicular directions (＋), and the SE
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increased further, up to approximately 20 dB, for five layers oriented in in four directions ( ). In other words, depending on how the spinnable MWNT layers are
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oriented, the resulting SE varied significantly. This means that this composite material was very effective for EMI shielding.
Moreover, SE of MBPBT was closely related to its specific electrical resistance. Figure 4 c) demonstrated the volume resistance in the horizontal direction for both samples decreased as SE increased. However, the rates of decrease in the specific
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ρ(ohm-cm) = Rtd / l,
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electrical resistance (ρ) were quite different. These values were calculated from
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where R is the linear resistance, t is the thickness of the material, d is the depth, and l is the width. The specific volume resistance for the plaid pattern of multi-layered MWNTs was found to be relatively high, but the value decreased from 6.73*10−3 (Ω-cm: 5 + 5 layers) to 9.70*10−4 (Ω-cm: 40 + 40 layers) as the number of layers of MWNTs increased. On the other hand, for the parallel pattern of multi-layered MWNTs, the measured value was relatively low, decreasing slightly from 4.03*10−4 (Ω-cm: 10 layers) to 1.20*10−4 (Ω-cm: 80 layers). Hence, this research confirmed that the alignment
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direction of the MWNTs caused a big difference in the specific volume resistance, and the shielding effect was maximized when the resistance was the lowest as the number of MWNTs increased.
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Furthermore, the Simon formula showed that this relationship depended strongly on the conductivity, which was the reason the silver nanowires were added;[7, 10, 30, 31]
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EMI shielding effectiveness (SE) = 50 + 10 log (σ/f ) + 1.7t
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Here, σ is the electrical conductivity, f is the frequency, and t is the thickness of the shielding material. Figure S6 a) showed conductivity in the parallel and plaid pattern of 5, 10, 20 and 40 multilayered MWNTs per stack based on the parallel measurement direction. Based on the measurement direction, conductivity was measured in the
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parallel pattern of 5, 10, 20 and 40 multilayered MWNTs per stack under two probe system as shown in Figure S6 b). In the parallel pattern of the 5, 10, 20 and 40 multilayered MWNTs per stack, the first 5, 10, 20, and 40 layers and the remained 5, 10,
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20 and 40 layers were also the same direction, which created many ways where
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electrons were easily able to move in the distance. On the other hand, the direction of the first layers and the remained layers were different, which means that the ways where electrons move relatively decreased in the plaid pattern of multi-layered MWNTs, which caused that conductivity was also decreased. However, EMI shielding effectiveness of the plaid pattern of the multilayerd MWNTs was high that the plaid pattern of multilayered MWNTs considered a movement property of the EM wave. This means that an incident EM wave was easily able to be admitted or transmitted in only one direction when the direction of the spinnable MWNTs was parallel to the oscillating
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direction of the EM, while the EM waves that flow only in one direction react with the vertically placed spinnable MWNTs and then were largely reflected or absorbed as shown in Figure 1 a). From the results, conductivity in the parallel pattern of the
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spinnable MWNTs was higher than that in any other cases when it was measured by the parallel measurement direction. Also, increase of the number of the spinnable MWNTs enhanced conductivity and EMI SE, which was correspondent with the Simon formula.
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However, the result regarding the relationship between EMI SE and conductivity was not matched with the formula when the spinnable MWNTs was highly aligned.
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Magnetic particles wrapped with the silver nanowires interacted with the EMI, even though this was not a significant effect for enhancing SE, as illustrated in Figure 4 d). The samples with and without magnetic particles were compared while increasing the number of MWNTs (2 + 2, 5 + 5, 10 + 10, 20 + 20, 40 + 40 layers), as shown in
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Figure 4 d). When the number of layers was small, we obtained a difference of 4 dB for 2 (2 + 2) and 5 (5 + 5) layers. On the other hand, the difference was only about 0.6 dB for 10 (10 + 10) or more layers, as shown in Figure 4 d). This shows that the magnetic
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permeability plays a large role when the number of layers of MWNTs is small, but the magnetic particles did not have much effect for larger numbers of layers.[1]
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Furthermore, the results were related to interfacial polarization, which was affected by stronger coupling at a gap among Fe3O4 and a heterogenous condition between the spinnable MWNTs and Fe3O4. However, the Fe3O4 could lead a decrease of conductivity, which resulted in a decrease of permittivity because efficiency of dipoles decreased through alternation of electrical vector of incident EM radiation. Hence, to increase the conductivity, the silver nanowire was inserted with Fe3O4.
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In addition, because the MBPBT was also very flexible, there was no problem in bending it through 180° without compromising its performance beyond the bending radius of existing graphene materials or MXene. This was due to the continuous,
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reticulated architecture of the spinnable MWNTs with BPBT.[20] Figure 5 a) showed the dielectric constant of another sample, which was measured again after bending it through 180°, and the values in the dielectric constants were almost identical. This was
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better than for any other film type of EMI shielding material. By utilizing this flexibility, it would be possible to apply this new composite material to many small electronic
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devices, such as portable and wearable smart devices and military equipment. To illustrate this, Figure 5 b) showed that MBPBT could be attached as a hinge of a small
4. Conclusions
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box.
In conclusion, this research demonstrated that the EMI SE was maximized by using a plaid pattern of spinnable MWNTs at X-band frequency range. Hence, we achieved
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commercial-grade shielding effect (over 20 dB) for any electronic devices. Also, the
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value in EMI shielding effectiveness was ultimately determined by the direction and number of layers of MWNTs. This means that a filter type of the spinnable MWNTs was actively able to handle the directionality and movement of unpolarized EMI propagation. Furthermore, we also confirmed that the dielectric constant of MBPBT was relatively high because of the interactions between the BPBT and the spinnable MWNTs when external electromagnetic radiation was applied. This verified that the disparity between two adjacent spinnable MWNTs with BPBT caused electrical charge accumulation and polarization on the surfaces of the MWNTs. Moreover, the MBPBT
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was characterized by its strong mechanical advantage (bending radius 180°) and excellent adhesiveness due to the characteristics of PDMS.
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Acknowledgments
This work was supported in Korea by the Creative Research Initiative Center for SelfPowered Actuation, the Korea-US Air Force Cooperation Program (Grant No.
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2013K1A3A1A32035592), and the National Research Foundation (Grant No. 2016R1C1B2012340) of the Ministry of Science, ICT & Future Planning (MSIP). The
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spinnable MWNTs were provided by LINTEC of America, INC.
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Figure 1. a) Schematic of a plaid pattern formed by spinnable MWNTs with BaTiO3, b) Illustration of the fabrication of a plaid pattern of spinnable MWNTs on a Teflon plate,
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Fe3O4/AgNW.
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c) fabrication processes of the MBPBT containing BPBT and composite of
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Figure 2. SEM images of a) multi-layered cross-sectional view of the EMI shielding material, b) magnetic particles wrapped by aligned MWNT sheets, c) TEM image of a plaid pattern fabricated from the spinnable MWNTs (2+2), SEM images of d) the
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PDMS containing BaTiO3, e) magnetic particles coated by silver nanowires.
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Figure 3. a) Comparison of EMI shielding efficiency of MBPBTs having perpendicular and parallel alignments of MWNTs (2 + 2 vs 2 ll 2), b) analysis of the shielding
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efficiency consisting of both absorption and reflection, c) dielectric constant of MBPBT having a perpendicular and a parallel alignment of MWNTs, d) permeability of MBPBT
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having a perpendicular and a parallel alignment of MWNTs, at X-band frequency range (8.2-12.4 GHz).
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Figure 4. a) The EMI SE for 2 (2 + 2), 5 (5 + 5), 10 (10 + 10), 20 (20 + 20), and 40 (40 + 40) layers of MWNTs with MBPBT. b) Comparison of the EMI SE based on the
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orientations of the spinnable MWNTs (20 + 20 vs 20 ll 20), c) Change in the specific volume resistance for the parallel and plaid patterns of multilayered MWNTs. d)
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Comparison of the EMI SE of MBPBT with and without magnetic particles and silver nanowires.
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Figure 5. a) Change in real part of dielectric constant before and after bending the sample. b) Optical images illustrating the mechanical property of MBPBT wrapped
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around as a hinge of a small box.