Influence of lengths of millimeter-scale single-walled carbon nanotube on electrical and mechanical properties of buckypaper

Nanoscale Research Letters, Dec 2013

The electrical conductivity and mechanical strength of carbon nanotube (CNT) buckypaper comprised of millimeter-scale long single-walled CNT (SWCNT) was markedly improved by the use of longer SWCNTs. A series of buckypapers, fabricated from SWCNT forests of varying heights (350, 700, 1,500 μm), showed that both the electrical conductivity (19 to 45 S/cm) and tensile strength (27 to 52 MPa) doubled. These improvements were due to improved transfer of electron and load through a reduced number of junctions for longer SWCNTs. Interestingly, no effects of forest height on the thermal diffusivity of SWCNT buckypapers were observed. Further, these findings provide evidence that the actual SWCNT length in forests is similar to the height.

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Influence of lengths of millimeter-scale single-walled carbon nanotube on electrical and mechanical properties of buckypaper

Nanoscale Research Letters Influence of lengths of millimeter-scale single-walled carbon nanotube on electrical and mechanical properties of buckypaper Shunsuke Sakurai Fuminori Kamada Don N Futaba Motoo Yumura Kenji Hata The electrical conductivity and mechanical strength of carbon nanotube (CNT) buckypaper comprised of millimeterscale long single-walled CNT (SWCNT) was markedly improved by the use of longer SWCNTs. A series of buckypapers, fabricated from SWCNT forests of varying heights (350, 700, 1,500 μm), showed that both the electrical conductivity (19 to 45 S/cm) and tensile strength (27 to 52 MPa) doubled. These improvements were due to improved transfer of electron and load through a reduced number of junctions for longer SWCNTs. Interestingly, no effects of forest height on the thermal diffusivity of SWCNT buckypapers were observed. Further, these findings provide evidence that the actual SWCNT length in forests is similar to the height. Carbon nanotube; Buckypaper; Tube length Background The effective transfer of phonons, electrons, and load is known to increase with longer carbon nanotubes (CNTs) within CNT agglomerates. For example, in the percolation theory, electron transfer is expected to be achieved with a lesser number of CNTs by the use of longer CNTs in accordance with the relation Nc = 5.71 /L2s, where Nc and Ls are percolation threshold and CNT length, respectively [ 1-4 ]. For example, higher electrical conductivity was observed for transparent conductive films using network thin films of longer CNTs [ 5,6 ]. In addition, Miyata el al. reported a field effect transistor (FET) with high mobility using long single-walled CNTs (SWCNTs) [ 7 ]. Further, in CNT/polymer composites, the beneficial effect of CNT length on the efficiency of phonon/electron transport and interfacial load transfer has been reported [ 8-11 ]. Such superiority in properties from long CNTs originates from the fewer CNT junctions, which interrupt phonon, electron, and load transfer, in a network structure of CNTs required to span the material. Although these reports suggest the advantages of long CNTs on electron, thermal, and mechanical properties of a CNT assembly, this point has not been explicitly demonstrated experimentally. In other words, almost all the above experiments have employed only short CNTs, on the order of micrometers, with only one exceptional report by Zhu et al., who reported on the properties of composite of multiwalled CNTs with thick diameters (approximately 40 to 70 nm) and bismaleimide (BMI) [8]. Particularly, there has been no report on the effect of length on the properties of SWCNTs exceeding 1 mm. There are three reasons why research on the CNT length dependence of various properties of CNT assemblies has been difficult. First, the synthesis of long CNTs with uniform length in a large quantity is difficult. For example, Wang et al. reported the synthesis of long single-wall CNTs with a maximum length of 18.5 cm, but there were substantial variations in CNT length [ 12 ]. Cao et al. reported an interesting approach for lengthtunable CNT growth, but the length did not reach to millimeter scale [ 13 ]. Furthermore, several groups reported the methods for classifying long/short CNTs, but this was not applied to CNTs that were longer than 10 μm in length [ 14-17 ]. Secondly, due to the tight entanglement among CNTs, the dispersion of CNTs without CNT scission is difficult. Ultrasonic agitation, which has been typically employed as a dispersion method, is known to shorten CNTs as it disentangles them [18]. Finally, there is no available method to measure the lengths of individual CNTs longer than 100 μm. CNTs with lengths of several micrometers have been evaluated by atomic force microscopy (AFM) [ 8-11,14-17 ], but this method encounters extreme difficultly when obtaining statistically significant data for long CNTs. Using water-assisted chemical vapor deposition (CVD), we reported the synthesis of a vertically aligned SWCNT array (SWCNT forest) with height exceeding a millimeter [ 19 ]. The SWCNT forests possessed several excellent structural properties, such as long length, high purity, and high specific surface area. This development opened up the potential for various new applications of CNTs, such as high-performance super-capacitors [ 20-23 ] and highly durable conductive rubbers [ 24,25 ]. Subsequently, many groups reported the growth of long SWCNTs. For example, Zhong et al. reported the growth of SWCNT forests reaching 0.5 cm in length [ 26 ]. Hasegawa et al. reported growth of SWCNT forests of several millimeters in length without an etching agent (water) [ 27 ]. Numerous studies have also reported the synthesis of multiwalled CNT forests [ 28-30 ]. However, the following points remain unclear at present: the correlations between forest height and (1) the actual CNT length and (2) the electrical, thermal, and mechanical properties after formation (...truncated)


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Shunsuke Sakurai, Fuminori Kamada, Don N Futaba, Motoo Yumura, Kenji Hata. Influence of lengths of millimeter-scale single-walled carbon nanotube on electrical and mechanical properties of buckypaper, Nanoscale Research Letters, 2013, pp. 546, Volume 8, Issue 1, DOI: 10.1186/1556-276X-8-546