Relationship between Mechanical and Electrical Properties of

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Relationship between Mechanical and Electrical Properties of Continuous Polymer-Free Carbon Nanotube Fibers by Wet-Spinning Method and Nanotube-Length Estimated by Far-Infrared Spectroscopy Xueli Wu,† Takahiro Morimoto,†,‡ Ken Mukai,†,‡,§ Kinji Asaka,†,‡,§ and Toshiya Okazaki*,†,‡ †

Technology Research Association for Single Wall Carbon Nanotubes (TASC), Tsukuba 305-8565, Japan CNT-Application Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8565, Japan § Inorganic Functional Materials Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Osaka, 563-8577, Japan ‡

S Supporting Information *

ABSTRACT: Neat carbon nanotube (CNT) fibers produced by wet spinning methods offers a potential for high-strength and electrically conductive lightweight materials. For improving their performances, it is necessary to understand how each manufacturing process affects the raw CNTs and implicates the effects in the fiber properties. Recently, we found that the lengths of the clean CNT channels can be estimated by far-infrared (FIR) spectroscopy based on the plasmon resonance model. In this paper, the relationship between the mechanical properties and electric conductivities of the neat CNT fibers, and the lengths of the constituent CNTs are systematically studied by using different types of single-walled CNTs (SWCNTs) with various diameters and different dispersing times. Irrespective of the type of CNTs or the tube diameters, Young moduli, fracture strengths, and electric conductivities of the CNT fibers were found to be related to the CNT lengths estimated from the FIR spectra. The results prove that the evaluation of CNT length by the FIR spectroscopy is a highly useful method to optimize the processing conditions as well as to select the proper CNTs for fabricating high-performance CNT-based materials.

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INTRODUCTION Carbon nanotubes (CNTs) consist of a seamless cylinder of a graphitic sheet capped by hemispherical ends composed of pentagons and hexagons.1,2 Due to their extraordinary electrical and mechanical properties, CNTs are widely regarded as very attractive nanomaterials.3,4 Actually, CNT production capacity has rapidly increased worldwide as well as the continuous grow of the numbers of CNT-related papers and patents.5 Most products using CNTs today incorporate CNTs from the dispersion in solvents or polymer matrices. For commercialization of these products, the physical properties of CNTs in the dispersion or matrix must be monitored to control the qualities of the products. The CNT length is one of the most important parameters for manufacturing the quality-controlled CNT products. Direct © 2016 American Chemical Society

imaging techniques such as atomic force microscope and scanning electron microscope (SEM) have usually been used to measure the CNT length. However, these techniques require tremendous numbers of the CNT observations, which is timeconsuming and labor intensive. On the other hand, we previously reported that the length of the CNTs can be estimated by a simple spectroscopy, in which the peak position of the farinfrared (FIR) peak is used.6−8 Because the observed FIR peak can be explained by the one-dimensional plasmon model, the length of the clean and straight CNT portion between defects or kinks can be deduced (effective CNT length).6,7 Received: July 6, 2016 Revised: August 21, 2016 Published: August 22, 2016 20419

DOI: 10.1021/acs.jpcc.6b06746 J. Phys. Chem. C 2016, 120, 20419−20427

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Figure 1. Injection images of SG-CNT suspensions (0.28 wt %) into IPA with different dispersing times of (a) 10, (b) 15, (c) 30, and (d) 60 min (Inset: SEM images of each CNT fiber, scale bar = 10 μm).

Wet Spinning. The following is a typical procedure for fabricating CNT fibers. First, 50 mg of SWCNTs was suspended in an aqueous solution (24.5 g) containing 450 mg of SC, which was then stirred and sonicated for 30 min at 35 °C using a sonic stirrer (Nissei model USS-1 ultrasonic stirrer, 40 kHz, 100 W) to predisperse CNTs into solution. This mixture was then sonicated for a further length of time using a horn-type ultrasonic probe (Nissei model US-50 ultrasonic generator, 28 kHz, 50 W). The CNT-dispersed solution thus obtained was then injected into IPA through a nozzle to produce a CNT fiber. The final CNT fiber was obtained by drying, after the directly obtained CNT fibers had been immersed in water for several hours to eliminate any residual surfactants. Characterization. FIR spectra were measured using an FTIR spectrometer (Vertex 80v: Bruker Optics) in the 70−8000 cm−1 range and a THz-TDS system (TR-1000: Otsuka Electronics) in the 4−70 cm−1 range. FIR spectral profile around the peak was fitted by a quadratic polynomial function to obtain the FIR peak position. Resonance Raman spectra were measured using a triple-grating T64000 monochromator system (Horiba JY) with diode-pumped solid-state lasers (Spectra Physics; 532 nm). All optical measurements were performed using nonpolar light irradiation. The electric conductivities of the CNT fibers were evaluated using a four-probe DC current method; in which a linear sweep of current was applied from the outer probe electrodes, and the resulting voltage was measured by inner probe electrodes. Current−voltage curves were obtained using a Hokuto Denko model HA-501G potentio/galvanostat with a Yokogawa Electric Corporation FG200 waveform generator. Stress−strain curves of the CNT fibers were recorded using a Seiko Instruments model TMA/SS 6000 thermal stress−strain measurement instrument, which was also utilized for obtaining their Young’s moduli and fracture strengths.

To preserve superior properties in macroscopic CNT-based structures, the production of fibers composed of CNTs offers a potential for high-strength and lightweight materials that are also thermally and electrically conductive.9−12 There are two approaches for fabricating CNT fibers: wet spinning13,14 and dry spinning.9,15−20 The wet spinning is simpler and more straightforward than the dry spinning, so it is easily scaled up to satisfy the production demands of industry. Recently, neat CNT fibers have been produced by a novel wet spinning method without a polymer coagulating solution or strong acid solvent by our research group.21 A free-standing CNT fiber can be fabricated from a CNT-dispersed solution with a surfactant, despite the use of an organic coagulating solvent. The high-alignment of CNTs in the fiber was achieved by a dry stretching process. Indeed, the electric conductivity of the stretched fiber reached as high as 14284 S cm−1, which was higher than those produced by conventional wet spinning methods (10 S cm−1),13 improved wet spinning methods (5000 S cm−1),12 and even some dry spinning methods (8300 S cm−1).18 In this paper, we systematically investigate the relationship between the mechanical and electrical properties of the CNT fibers and the CNT lengths estimated from the FIR peaks by using two types of SWCNTs (supergrowth CNTs (SG-CNTs)22 and enhanced direct injection pyrolytic synthesis CNTs (eDIPS-CNTs)23) with various tube diameters. Furthermore, the dispersion time dependences on the fiber properties are also examined. Interestingly, Young’s moduli, fracture strengths, and electric conductivities of CNT fibers were found to be closely related to the obtained CNT lengths, irrespective of tube types and diameters. This demonstrates that the FIR spectroscopy is an effective and convenient method to estimate CNT lengths during the fabricating processes.

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EXPERIMENTAL SECTION

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Materials. Two types of SWCNTs synthesized by the SG and the e-DIPS methods were used in this work.22,23 Sodium cholate (SC) and isopropyl alcohol (IPA) were used as received from Wako Pure Chemical Industries Co., Ltd.

RESULTS AND DISCUSSION SG-CNT Fibers. SG-CNTs were dispersed into water with the help of SC as a surfactant by sonication from 10 to 60 min at a 20420

DOI: 10.1021/acs.jpcc.6b06746 J. Phys. Chem. C 2016, 120, 20419−20427

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Figure 2. Mechanical and electrical properties of 0.28 wt % SG-CNT fibers: (a) Young’s moduli, (b) fracture strengths, and (c) electric conductivities.

Figure 3. (a) Resonance Raman and (b) FIR spectra of SG-CNTs (0.28 wt %) in suspensions with various dispersing times.

Figure 4. Mechanical and electrical properties of SG-CNT fibers as a function of the G/D ratio: (a) Young’s moduli, (b) fracture strengths, and (c) electric conductivities. 20421

DOI: 10.1021/acs.jpcc.6b06746 J. Phys. Chem. C 2016, 120, 20419−20427

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Figure 5. Mechanical and electrical properties of SG-CNT fibers as a function of the effective CNT length: (a) Young’s moduli, (b) fracture strengths, and (c) electric conductivities.

Figure 6. Injection images of e-DIPS-1.7 suspension into IPA with different ultrasonic dispersing times of (a) 0 min, (b) 7 min, (c) 30 min, (d) 1 h, (e) 4 h, and (f) 8 h (Inset: SEM images of each CNT fiber, scale bar = 50 μm).

concentration of 0.28 wt % (0.28 wt % SG-CNT). Figure 1 shows their injection images into the IPA solutions, in which the SGCNTs suspension with 60 min (Figure 1d) sonication did not form good fiber. The SEM images of the fibers were shown in the insets. To explore the mechanical and electrical properties of the CNT fibers from 0.28 wt % SG-CNT suspensions with different dispersing times, we measured Young’s moduli, fracture strengths, and electric conductivities of the produced CNT fibers (Figure 2). Both Young’s moduli and electric conductivities first increase, then decrease as the dispersing time increases, and finally become very low when the suspension is dispersed for 60 min.

Raman spectroscopy is usually used to estimate the quality or purity of CNTs through the G-band (∼1582 cm−1) and D-band (∼1350 cm−1) intensity ratio (G/D).24 G-band is the primary Raman active mode in graphite and provides a good representation of the sp2-carbon in planar sheet configurations. The D-band, known as the disorder or defect mode, originates from the edge of the open end of CNTs and defects in the tube walls. Figure 3a shows the Raman spectra of SG-CNTs thin films that were obtained after filtering each suspension. The G/D values are 2.4, 2.3, 2.2, and 2.9 for the 10, 15, 30, and 60 min processed samples, respectively. Almost similar G/D values might suggest that the sonication process did not affect the surface disorder of SG-CNTs very much. 20422

DOI: 10.1021/acs.jpcc.6b06746 J. Phys. Chem. C 2016, 120, 20419−20427

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Figure 7. Mechanical and electrical properties of e-DIPS-1.7 fibers: (a) Young’s moduli, (b) fracture strengths, and (c) electric conductivities.

Figure 8. Raman spectra (a) and FIR spectra (b) of e-DIPS-1.7 suspensions with different dispersing times.

be observed between these physical properties and Leff as shown in Figure 5, whereas such correlation is barely seen between the fiber properties and the G/D ratio (Figure 4). These results strongly suggest that the properties of CNT fibers correlate well with Leff in the suspension and Leff is a good parameter to optimize the experimental conditions for high-performance CNT fibers. Effects of Sonication Process for e-DIPS-CNT Fibers. To study the relationship between fiber properties and the constitute CNTs in more detail, we prepared CNT fibers by using the other type of SWCNTs, e-DIPS-CNTs, with an average diameter of 1.7 nm (e-DIPS-1.7). The suspensions of e-DIPS-CNTs were prepared by using 0 min to 8 h sonication under the same experimental conditions as those of SG-CNTs as described above. Note that the “0 min” suspension means the sample dispersed without horn-type sonication. Only the predispersion process by a sonic-stirrer was used for preparing the suspension (see Experimental Section). Based on the injection images in Figure 6, the suspensions can be injected into perfect fiber until for 1 h processed samples. Longer sonication time is needed for e-DIPS-CNT fibers than SG-CNT samples because the lengths of e-DIPS-CNTs are longer than those of SG-CNT, which requires longer sonication times to be debundled. Relatively

Figure 3b shows the FIR optical density spectra of the SGCNTs thin films. A broad and strong peak can be seen at approximately 342, 300, 311, and 420 cm−1 for 10, 15, 30, and 60 min processed samples, respectively. As the sonication duration increases, the peak maximum shifts toward higher wavenumbers. The apparent shifts in the FIR peak positions strongly suggest the shortening in the CNTs length.6,7 We also characterized the SG-CNTs in the suspensions at a concentration of 0.20 wt % (0.20 wt % SG-CNTs) with various sonication times (see Supporting Information, Figures S1−S3). The fiber properties were severely compromised after 60 min sonication, which was similar to those of 0.28 wt % SG-CNTs. Young’s moduli, fracture strengths, and electric conductivities of 0.28 and 0.20 wt % SG-CNT fibers (see Figures 2 and S2) are plotted as functions of the G/D ratio and the CNTs length estimated from the FIR peak positions (Figures 4 and 5). The effective CNTs length (Leff) were calculated from the observed FIR peak positions on the basis of the formula proposed by Nakanishi and Ando,25 where the diameter of SG-CNTs is assumed to be 3 nm. The experimental errors of the FIR peak positions were less than 1%. Here we should point out that Leff corresponds to the length of the clean and straight CNT channel between defects or kinks.6,7 Apparently, positive correlation can 20423

DOI: 10.1021/acs.jpcc.6b06746 J. Phys. Chem. C 2016, 120, 20419−20427

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Figure 9. Injection images of e-DIPS suspension into IPA with different diameters of (a) 1.0, (b) 1.3, (c) 1.4, (d) 1.7, and (e) 2.0 nm (Inset: SEM images of each CNT fiber, scale bar = 50 μm).

Figure 10. Mechanical and electrical properties of e-DIPS fibers with different diameters: (a) Young’s moduli, (b) fracture strengths, and (c) electric conductivities.

thick fibers were obtained for the suspension with 4 h (Figure 6e) and 8 h (Figure 6f) sonication. Young’s moduli, fracture strengths, and electric conductivities of the e-DIPS-1.7 fibers are shown in Figure 7. For the longer dispersing times (4 and 8 h), both mechanical and electrical properties become lower. The e-DIPS-1.7-CNTs in the suspensions were characterized by resonance Raman and FIR spectroscopy as shown in Figure 8. The obtained G/D values were 110.9, 114.8, 47.6, 33.2, 17.4, and 13.5 for 0 min, 7 min, 30 min, 1, 4, and 8 h processed samples, respectively (Figure 8a). As the sonication time increases, the crystallinity of the CNTs decreases. The FIR spectra of each CNT are shown in Figure 8b. The apparent higher FIR peak

positions for the samples with 4 and 8 h sonication indicate that the CNTs were shortened by the sonication processes. The lower fiber properties of the longer-processed samples (Figure 7) can be explained by the shortening in CNTs length. The details will be discussed later, together with the results of e-DIPS-CNTs having the other diameters. e-DIPS-CNT Fibers with Various Tube Diameters. Advantageously, the e-DIPS method can precisely control the tube diameter of the synthesized SWCNTs.23 The e-DIPS-CNTs with average diameters of 1.0 nm (e-DIPS-1.0), 1.3 nm (e-DIPS1.3), 1.4 nm (e-DIPS-1.4), 1.7 nm (e-DIPS-1.7), and 2.0 nm (eDIPS-2.0) were dispersed in SC aqueous solution by a sonicstirrer for 30 min (predispersion process, see Experimental 20424

DOI: 10.1021/acs.jpcc.6b06746 J. Phys. Chem. C 2016, 120, 20419−20427

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Figure 11. (a) Resonance Raman and (b) FIR spectra of e-DIPS suspensions with different diameters.

Figure 12. Mechanical and electrical properties of various diameter e-DIPS fibers with different sonication times as a function of the G/D ratio: (a) Young’s moduli, (b) fracture strengths, and (c) electric conductivities.

length based on the FIR measurements. All properties correlate well with the CNTs length rather than G/D value. Specifically, the length-dependence of mechanical and electrical properties is clearer, except for one data of e-DIPS-2.0 at Leff = 5200 nm (Figure 13). This might be due to the fact that larger diameter CNTs are difficult to debundle, which leads to lower fiber properties.26,27 Relationship between Fiber Properties and CNT Length. Finally, Figure 14 shows the relationship between the CNTs length and the properties of all SG-CNT and e-DIPSCNT fibers studied here. Regardless of the type of SWCNTs and dispersing time, the fiber properties definitely exhibit positive linear dependence on Leff in suspensions. Both mechanical and electrical properties of e-DIPS-CNT fibers are far higher than those of SG-CNTs because the e-DIPS-CNTs are longer than SG-CNTs. Almost linear correlations between the fiber properties and the CNTs length observed here are supported by the theoretical prediction. This suggests that the fiber strength is linearly proportional to the length up to 10 μm for CNTs with a 1 nm diameter.28 The present observations indicate that damage on the tube walls severely disrupts the superior mechanical and electrical properties of CNTs in fiber forms.

Section) and then injected into IPA (Figure 9). It is clearly seen that only e-DIPS-1.0 cannot form good fiber. SEM image of its fiber also shows low alignment of CNTs. The properties of each e-DIPS fiber are shown in Figure 10, in which both the mechanical and electrical properties of e-DIPS-1.0 are much lower than those of the others. Figure 11 shows resonance Raman and FIR spectra of e-DIPSCNTs thin films that were obtained after filtering each suspension. The G/D values are 13.9, 67.5, 50.3, 110.9, and 77.8 for e-DIPS-1.0, −1.3, −1.4, −1.7, and −2.0, respectively (Figure 11a). The very low G/D value of e-DIPS-1.0 indicates low crystallinity. Because the Raman scattering of CNTs is dominated by the resonance process, the obtained spectra show different shapes. The FIR peak positions are 92.9, 34.4, 16.7, 40.9, and 9.9 cm−1 for e-DIPS with 1.0, 1.3, 1.4, 1.7, and 2.0 nm in diameter, respectively (Figure 11b). Obviously, the peak position of e-DIPS-1.0 is much higher than the others. The result strongly suggests that the length of e-DIPS-1.0 is shorter, resulting in the lower fiber properties (Figure 10). On the other hand, the properties of e-DIPS-CNT fibers are highest for e-DIPS-1.4 (Figure 10). Because the e-DIPS-1.4 lengths are relatively long, they may form tight bundles in the fiber. Figures 12 and 13 show (a) Young’s moduli, (b) fracture strengths, and (c) electric conductivities of all e-DIPS fibers described above as functions of the G/D ratio and the CNTs 20425

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Figure 13. Mechanical and electrical properties of various diameter e-DIPS fibers with different sonication times as a function of CNTs length: (a) Young’s moduli, (b) fracture strengths, and (c) electric conductivities.

Figure 14. Mechanical and electrical properties of all SG-CNT and e-DIPS fibers as a function of Leff: (a) Young’s moduli, (b) fracture strengths, and (c) electric conductivities.

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CONCLUSION In summary, the CNT fiber properties produced by the wetspinning method were systematically investigated by using two types of SWCNTs with different diameters and various sonication times. The CNTs in the suspensions were characterized by the resonance Raman and FIR spectroscopy. The Young’s moduli, fracture strengths, and electric conductivities of the fabricated fibers strongly correlate with the effective CNTs length estimated by the FIR spectroscopy irrespective of the type of CNTs and the tube diameters. Because the FIR method can estimate the effective tube lengths for CNTs with different diameters and types, systematic study on the fiber

performance and the effective CNT length was possible. The present findings strongly suggest that FIR spectroscopy can provide a good index parameter, the effective CNT length, to select the proper CNTs for fibers and monitor the tube length during the dispersion processes.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.6b06746. Injection images of 0.20 wt % SG-CNT fibers, mechanical properties and electric conductivity of 0.20 wt % SG-CNT 20426

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fibers, and FIR and Raman spectra of 0.20 wt % SG-CNT suspensions (PDF).

K. Anisotropic carbon nanotube papers fabricated from multiwalled carbon nanotube webs. Carbon 2011, 49, 2437−2443. (18) Li, Y. L.; Kinloch, I. A.; Windle, A. H. Direct spinning of carbon nanotube fibers from chemical vapor deposition synthesis. Science 2004, 304, 276−278. (19) Zhong, X. H.; Li, Y. L.; Liu, Y. K.; Qiao, X. H.; Feng, Y.; Liang, J.; Jin, J.; Zhu, L.; Hou, F.; Li, J. Y. Continuous multilayered carbon nanotube yarns. Adv. Mater. 2010, 22, 692−696. (20) Wang, J. N.; Luo, X. G.; Wu, T.; Chen, Y. High-strength carbon nanotube fibre-like ribbon with high ductility and high electrical conductivity. Nat. Commun. 2014, 5, 3848−3855. (21) Mukai, K.; Asaka, K.; Wu, X.; Morimoto, T.; Okazaki, T.; Saito, T.; Yumura, M. Wet spinning of continuous polymer-free carbon-nanotube fibers with high electrical conductivity and strength. Appl. Phys. Express 2016, 9, 055101. (22) Hata, K.; Futaba, D. N.; Mizuno, K.; Namai, T.; Yumura, M.; Iijima, S. Water-assisted highly efficient synthesis of impurity-free singlewalled carbon nanotubes. Science 2004, 306, 1362−1364. (23) Saito, T.; Ohshima, S.; Okazaki, T.; Ohmori, S.; Yumura, M.; Iijima, S. Selective diameter control of single-walled carbon nanotubes in the gas-phase synthesis. J. Nanosci. Nanotechnol. 2008, 8, 6153−6157. (24) Dresselhaus, M. S.; Dresselhaus, G.; Saito, R.; Jorio, A. Raman spectroscopy of carbon nanotubes. Phys. Rep. 2005, 409, 47−99. (25) Nakanishi, T.; Ando, T. Optical response of finite-length carbon nanotubes. J. Phys. Soc. Jpn. 2009, 78, 114708−114717. (26) Tersoff, J.; Ruoff, R. S. Structural properties of a carbon-nanotube crystal. Phys. Rev. Lett. 1994, 73, 676−679. (27) Tange, M.; Okazaki, T.; Iijima, S. Selective extraction of largediameter single-wall carbon nanotubes with specific chiral indices by poly(9,9-dioctylfluorene-alt-benzothiadiazole). J. Am. Chem. Soc. 2011, 133, 11908−11911. (28) Behabtu, N.; Green, M. J.; Pasquali, M. Carbon nanotube-based neat fibers. Nano Today 2008, 3, 24−34.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: +81-29-861-4173. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Dr. K. Hata (AIST), Dr. D. N. Futaba (AIST), and Dr. T. Saito (AIST) for supplying us SG- and e-DIPS-CNTs. This paper is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

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REFERENCES

(1) Iijima, S.; Ichihashi, T. Single-shell carbon nanotubes of 1-nm diameter. Nature 1993, 363, 603−605. (2) Bethune, D. S.; Kiang, C. H.; De Vries, M. S.; Gorman, G.; Savoy, R.; Vazquez, J.; Beyers, R. Cobalt-catalysed growth of carbon nanotubes with single-atomic-layer walls. Nature 1993, 363, 605−607. (3) Ebbesen, T. W.; Lezec, H. J.; Hiura, H.; Bennett, J. W.; Ghaemi, H. F.; Thio, T. Electrical conductivity of individual carbon nanotubes. Nature 1996, 382, 54−56. (4) Ruoff, R. S.; Dong, Q.; Liu, W. K. Mechanical properties of carbon nanotubes: Theoretical predictions and experimental measurements. C. R. Phys. 2003, 4, 993−1008. (5) De Volder, M. F. L.; Tawfick, S. H.; Baughman, R. H.; Hart, A. J. Carbon Nanotubes: Present and Future Commercial Applications. Science 2013, 339, 535−539. (6) Morimoto, T.; Joung, S. − K.; Saito, T.; Futaba, D. N.; Hata, K.; Okazaki, T. Length-dependent plasmon resonance in single-walled carbon nanotubes. ACS Nano 2014, 8, 9897−9904. (7) Morimoto, T.; Okazaki, T. Optical resonance in far-infrared spectra of multiwalled carbon nanotubes. Appl. Phys. Express 2015, 8, 055101− 055104. (8) Morimoto, T.; Ikeda, Y.; Ichida, M.; Okazaki, T. Temperature dependence of plasmon resonance in single-walled carbon nanotubes. Phys. Rev. B: Condens. Matter Mater. Phys. 2016, 93, 195409. (9) Koziol, K.; Vilatela, J.; Moisala, A.; Motta, M.; Cunniff, P.; Sennett, M.; Windle, A. High-performance carbon nanotube fiber. Science 2007, 318, 1892−1895. (10) Zhao, Y.; Wei, J.; Vajtai, R.; Ajayan, P. M.; Barrera, E. V. Iodine doped carbon nanotube cables exceeding specific electrical conductivity of metals. Sci. Rep. 2011, 1, 83−87. (11) Villmow, T.; Pegel, S.; John, A.; Rentenberger, R.; Pötschke, P. Liquid sensing: Smart polymer/CNT composites. Mater. Today 2011, 14, 340−345. (12) Behabtu, N.; Young, C. C.; Tsentalovich, D. E.; Kleinerman, O.; Wang, X.; Ma, A. W. K.; Bengio, E. K.; ter Waarbeek, R. F.; de Jong, J. J.; Hoogerwerf, R. E.; et al. Strong, Light, Multifunctional fibers of carbon nanotubes with ultrahigh conductivity. Science 2013, 339, 182−186. (13) Vigolo, B.; Pénicaud, A.; Coulon, C.; Sauder, C.; Pailler, R.; Journet, C.; Bernier, P.; Poulin, P. Macroscopic fibers and ribbons of oriented carbon nanotubes. Science 2000, 290, 1331−1334. (14) Steinmetz, J.; Glerup, M.; Paillet, M.; Bernier, P.; Holzinger, M. Production of pure nanotube fibers using a modified wet-spinning method. Carbon 2005, 43, 2397−2400. (15) Jiang, K.; Li, Q.; Fan, S. Spinning continuous carbon nanotube yarns. Nature 2002, 419, 801. (16) Zhang, M.; Atkinson, K. R.; Baughman, R. H. Multifunctional carbon nanotube yarns by downsizing an ancient technology. Science 2004, 306, 1358−1361. (17) Inoue, Y.; Suzuki, Y.; Minami, Y.; Muramatsu, J.; Shimamura, Y.; Suzuki, K.; Ghemes, A.; Okada, M.; Sakakibara, S.; Mimura, H.; Naito, 20427

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