Electrical properties of carbon nanotube based fibers and their future use in electrical wiring Advanced Functional Materials 24, 3661 (2014)
A. Lekawa-Raus, J. Patmore, L. Kurzepa, J. Bulmer, K.K. Koziol

The production of continuous fibers made purely of carbon nanotubes has paved the way for new macro-scale applications which utilize the superior properties of individual carbon nanotubes. These wire-like macroscopic assemblies of carbon nanotubes were recognized to have a potential to be used in electrical wiring. Carbon nanotube wiring may be extremely light and mechanically stronger and more efficient in transferring high frequency signals than any conventional conducting material, being cost-effective simultaneously. However, transfer of the unique properties of individual CNTs to the macro-scale proves to be quite challenging. This Feature Article gives an overview of the potential of using carbon nanotube fibers as next generation wiring, state of the art developments in this field, and goals to be achieved before carbon nanotubes may be transformed into competitive products.

DOI: 10.1002/adfm.201303716
The effect of carbon nanotube orientation on erosive wear resistance of CNT-epoxy based compositesCarbon 73, 421 (2014)
J. Chen, I.M. Hutchings, T. Deng, M.S.A. Bradley, K.K. Koziol

Aligned carbon nanotube (CNT) polymer composites are envisioned as the next-generation composite materials for a wide range of applications. In this work, we investigate the erosive wear behavior of epoxy matrix composites reinforced with both randomly dispersed and aligned carbon nanotube (CNT) arrays. The aligned CNT composites are prepared in two different configurations, where the sidewalls and ends of nanotubes are exposed to the composite surface. Results have shown that the composite with vertically aligned CNT-arrays exhibits superior erosive wear resistance compared to any of the other types of composites, and the erosion rate reaches a similar performance level to that of carbon steel at 20° impingement angle. The erosive wear mechanism of this type of composite, at various impingement angles, is studied by Scanning Electron Microscopy (SEM). We report that the erosive wear performance shows strong dependence on the alignment geometries of CNTs within the epoxy matrix under identical nanotube loading fractions. Correlations between the eroded surface roughness and the erosion rates of the CNT composites are studied by surface profilometry. This work demonstrates methods to fabricate CNT based polymer composites with high loading fractions of the filler, alignment control of nanotubes and optimized erosive wear properties.

doi: 10.1016/j.carbon.2014.02.083
Electrothermal halogenation of carbon nanotube filmsCarbon 73, 259 (2014)
D. Janas, S. Boncel, K.K. Koziol

We report an innovative approach to halogenation of carbon nanotube (CNT) films. Application of bias voltage across horizontally aligned CNT films resulted in the electrothermal effect, which enabled us to chemically modify CNT films at the entirely controlled range of temperatures up to 300°C. Such heated CNT membranes were exposed to gaseous halogens (Cl2, Br2, I2) whilst their electrical properties were monitored. The experiments were carried out at room temperature and 100 – 300°C (in 50°C steps) until no further change in electrical resistance could be seen. The procedure lasted less than one minute, during which we were able to successfully introduce up to 6.7%, 6.0% and 1.5% at. of Cl, Br and I into the CNT framework. In parallel, we observed a permanent increase in conductivity of the films and mild purification of the starting material due to the removal of various carbon-oxygen functional groups.

doi: 10.1016/j.carbon.2014.02.062
Enhanced graphitization of c-CVD grown multi-wall carbon nanotube arrays assisted by removal of encapsulated iron-based phases under thermal treatment in argon Applied Surface Science 301, 488 (2014)
S. Boncel, K.K. Koziol

The effect of annealing on multi-walled carbon nanotube (MWCNT) arrays grown via catalytic Chemical Vapour Deposition (c-CVD) was studied. The treatment enabled to decrease number of defects/imperfections in the graphene walls of MWCNTs’, which was reflected in Raman spectroscopy by reduction of the ID/IG ratio by 27%. Moreover, the vertical alignment from the as-synthesized nanotube arrays was found intact after annealing. Not only graphitization of the nanotube walls occurred under annealing, but the amount of metal iron-based catalyst residues (interfering with numerous physicochemical properties, and hence applications of MWCNTs) was reduced from 9.00 wt.% (for pristine MWCNTs) to 0.02 wt.% as detected by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). This value, established by a new analytical protocol, is the lowest recorded by now for purified c-CVD MWCNTs and, due to operating under atmospheric pressure, medium temperature regime (as for annealing processes), reasonable time-scale and metal residue non-specificity, it could lay the foundation for commercial purification of c-CVD derived MWCNTs.

doi: 10.1016/j.apsusc.2014.02.108
Iodine monochloride as a powerful enhancer of electrical conductivity of carbon nanotube wiresCarbon 73, 225 (2014)
D. Janas, A.P. Herman, S. Boncel, K.K. Koziol

We report a new method to modify electrical properties of carbon nanotubes (CNTs). Single-, double- and multi-wall CNTs were subjected to treatment with a polar interhalogen compound, i.e. iodine monochloride (ICl) for 8 h at room temperature or briefly at 350°C to assess kinetics and thermodynamics of the reactions. The results showed a powerful p-doping, which enabled us to decrease electrical resistance of the material by more than 60% eventually reaching specific conductivity of 1.24 S m2 g-1. Functionalization of CNTs with halogen atoms resulted in evident changes to the material microstructure and composition. To illustrate viability of this technique for manufacturing highly conductive wires, we have produced an ICl-doped CNT-based USB cable. The tests unequivocally revealed that the cable could be successfully used for power or data transmission on the verge of USB 2.0 capabilities.

doi: 10.1016/j.carbon.2014.02.058
En route to controlled catalytic CVD synthesis of densely packed and vertically aligned nitrogen-doped carbon nanotube arraysBeilstein Journal of Nanotechnology 5, 219 (2014)
S. Boncel, S.W. Pattinson, V. Geiser, M.S.P. Shaffer, K.K.K. Koziol

The catalytic chemical vapour deposition (c-CVD) technique was applied in the synthesis of vertically aligned arrays of nitrogen-doped carbon nanotubes (N-CNTs). A mixture of toluene (main carbon source), pyrazine (1,4-diazine, nitrogen source) and ferrocene (catalyst precursor) was used as the injection feedstock. To optimize conditions for growing the most dense and aligned N-CNT arrays, we investigated the influence of key parameters, i.e., growth temperature (660, 760 and 860 °C), composition of the feedstock and time of growth, on morphology and properties of N-CNTs. The presence of nitrogen species in the hot zone of the quartz reactor decreased the growth rate of N-CNTs down to about one twentieth compared to the growth rate of multi-wall CNTs (MWCNTs). As revealed by electron microscopy studies (SEM, TEM), the individual N-CNTs (half as thick as MWCNTs) grown under the optimal conditions were characterized by a superior straightness of the outer walls, which translated into a high alignment of dense nanotube arrays, i.e., 5 × 108 nanotubes per mm2 (100 times more than for MWCNTs grown in the absence of nitrogen precursor). In turn, the internal crystallographic order of the N-CNTs was found to be of a ‘bamboo’-like or ‘membrane’-like (multi-compartmental structure) morphology. The nitrogen content in the nanotube products, which ranged from 0.0 to 3.0 wt %, was controlled through the concentration of pyrazine in the feedstock. Moreover, as revealed by Raman/FT-IR spectroscopy, the incorporation of nitrogen atoms into the nanotube walls was found to be proportional to the number of deviations from the sp2-hybridisation of graphene C-atoms. As studied by XRD, the temperature and the [pyrazine]/[ferrocene] ratio in the feedstock affected the composition of the catalyst particles, and hence changed the growth mechanism of individual N-CNTs into a ‘mixed base-and-tip’ (primarily of the base-type) type as compared to the purely ‘base’-type for undoped MWCNTs.

doi: 10.3762/bjnano.5.24
“Binary salt” of hexane-1,6-diaminium adipate and “carbon nanotubate” as a synthetic precursor of carbon nanotube/Nylon-6,6 hybrid materialsPolymer Composites 35, 523 (2014)
S. Boncel, J. Gorka, M.S.P. Shaffer, K.K.K. Koziol

A novel chemical approach was established to produce carbon nanotube/Nylon-6,6 hybrid materials from readily available substrates, that is, Nylon-6,6 salt and oxidized multiwall carbon nanotubes (O-MWCNTs). The key synthetic precursor hexane-1,6-diaminium adipate and “carbon nanotubate”—“Binary nanotube salt”—was obtained and isolated as stable and easy-to-handle solid in over 80% yield and with no nanotube losses. The final hybrid materials of various nanotube loadings were synthesized at 270°C and were easily purified from the homopolymer. Purified hybrids were comprehensively analyzed (yields and grafting ratios, SEM, TEM, FT-IR) revealing a two-phase characteristics—individually grafted nanotubes and cross-linked nanotube material. Isothermal TGA kinetic studies showed that in the “binary salts” diamine and diacid molecules were anchored to the nanotube outer shells and then held electrostatically enabling growth of polymer immobilized on O-MWCNTs (“grafting-from” mechanism). Depending on the density and type of nanotube functionalities and filler concentration in the “binary salt,” the O-MWCNT/Nylon-6,6 hybrids can be treated as hybrid material of a proportion of aliphatic polyamide and polyaramide properties.

doi: 10.1002/pc.22691
Ultra-pure single wall carbon nanotube fibres continuously spun without promoterScientific Reports 4, 3903 (2014)
C. Paukner, K.K. Koziol

We report a new strategy towards the control of carbon nanotube (CNT) structure and continuous fibre formation using a floating catalyst direct spinning CVD process. In the procedures used to date, a sulphur promoter precursor is added to significantly enhance the rate of CNT formation in the floating catalyst synthesis. Within the reaction zone, the rapidly grown nanotubes self-assemble into bundles, followed by their continuous spinning into fibres, yarns, films or tapes. In this paper we demonstrate a catalyst control strategy in the floating catalyst system, where the CNT formation process is independent of the presence of a promoter but leads to successful spinning of the macroscopic carbon nanotube assemblies with specific morphology, high purity (Raman D/G 0.03) and very narrow diameter range (0.8–2.5 nm). This can be achieved by the control of catalyst precursor decomposition and subsequent formation of homogeneous nano-sized catalyst particles.

doi: 10.1038/srep03903