Papers

12/2016
Thermal properties of continuously spun carbon nanotube fibresPhysica E (in press)
K. Koziol, D. Janas, E. Brown, L. Hao

As indicated by theory and experimental measurements individual carbon nanotubes (CNTs) have very high values of thermal conductivity. One of the challenges is to achieve high thermal conductivity in macroscopic assemblies of CNTs such as fibres, films and composites, paving the way to a wide range of applications. CNT fibres have tremendous potential in succeeding as the future materials for a variety of applications when properties at the nanoscale are translated to their macroscopic assemblies. In this paper we report the measurements of thermal conductivity of continuously spun CNT fibres and its dependence on temperature. Thermal conductivity measurements were performed using in-house built temperature sensing microscope probe. Specific thermal conductivity of CNT fibres showed an order of magnitude advantage over the traditional materials used for heat dissipation.

doi:10.1016/j.physe.2016.12.011
12/2016
Electrical transport in carbon nanotube fibresScripta Materialia (in press)
A. Lekawa-Raus, T. Gizewski, J. Patmore, L. Kurzepa and K. Koziol

Individual carbon nanotubes are highly interesting electrical conductors which could well complete with superconductors. Yet, the possibility of production of top-performance carbon nanotube electrical conductors beyond nanoscale, is the question currently challenging scientists.

This study discusses theoretical potential of macroscopic fibres made purely of carbon nanotubes, in charge transport and electrical applications. It also examines various aspects of their electrical conductivity including both direct and alternating current transport, weight-conductivity ratios, current density and doping issues. The reasons for the constraints in electrical transport in fibres manufactured today are explained, as are possible routes to achieving significant improvements in the performance.

doi:10.1016/j.scriptamat.2016.11.027
11/2016
Carbon nanotube fibers and films: synthesis, applications and perspectives of the direct-spinning method Nanoscale, 2016,8, 19475-19490
D. Janas and K. Koziol

The direct-spinning method of creation of CNT macroassemblies has received a lot of attention because of its simplicity to produce high-performance material without apparent limits to its size. CNT fibers or films have shown unparalleled properties and opened new areas of research and commercial development. The process designed more than a decade ago has already given interesting information about the basic science of nanomaterials, which in parallel led to the creation of the first prototypes with high potential of implementation in everyday life. Because of this, there has been growing interest in this technique with research articles coming into view from all around the world on a frequent basis. This review aims to summarize all the progress made in the direct-spinning process on a spectrum of fronts ranging from the study of complex synthesis parameters, material properties to its viable applications. The strong and weak points of the “Cambridge process” are carefully evaluated to put forward what challenges are most pressing. The future overlook puts the state of the art into perspective and suggests the prospective research directions.

doi:10.1039/C6NR07549E
10/2016
Printing of highly conductive carbon nanotubes fibres from aqueous dispersionMaterials & Design
D. Janas, S.K. Kreft and K. Koziol

Carbon nanotubes (CNT) fibres were printed from liquid suspension. The resulting fibres are highly conductive, with conductivity close to the one of standard CNT fibres, flexible and very versatile. The printed fibres are comparable to fibres that can be gained from direct spinning, carpet spinning and spinning from superacids, but offer broader range of composition and are simpler and safer to produce as no high-temperature equipment and dangerous chemicals need to be used. Any CNT material can be implemented, allowing the use of a variety of CNT structures, different densities of the fibres and various shapes for the final product.

doi:10.1016/j.matdes.2016.11.073
07/2016
The influence of metal nanoparticles on electrical properties of carbon nanotubesApplied Surface Science
D. Janas and K. Koziol

First, sputtering deposition of Au, Ag, Pt and Pd resulted in changes to the electrical resistance of carbon nanotube (CNT) films due to electron localization followed by creation of percolation pathways. Metal-CNT composites created this way showed different reaction of electrical resistance to temperature as well as thermal stability. Furthermore, their surface properties show much higher affinity towards aqueous media than as-made CNT films. Finally, we have developed an easy way of tailoring the size of metal clusters on the surface of CNT films depending on the employed deposition and heating conditions. Electrothermal sintering yielded metal clusters of controlled size that showed big potential for the application in catalyst-assisted chemical transformations

doi:10.1016/j.apsusc.2016.02.233
06/2016
Carbon nanotube-copper composites by electrodeposition on carbon nanotube fibersIn press, accepted manuscript, published online 3 June 2016
P-M. Hannula, A. Peltonen, J.Aromaa, D. Janas, M. Lundström, B.P. Wilson, K.Koziol, O. Forsén

Electrochemical deposition of copper on a carbon nanotube (CNT) fiber from a copper sulfate – sulfuric acid bath was studied in order to produce a carbon nanotube-copper composite wire. The high resistivity of the aerogel-spun fiber causes a non-uniform current distribution during deposition, which results in a drastic drop in the copper nuclei population density as sufficient overpotential is not available beyond a certain distance from the current feed point. Copper was found to fill the pores between CNT bundles from Focused Ion Beam (FIB) cut cross-sections confirming that aqueous based electrolytes can fill micropores between as-spun CNTs in a fiber network. The speed at which copper grows on the fiber surface was identified at ca. 0.08 mm/s with 1 mA applied current. The copper cladding showed columnar growth with a grain size an order of magnitude higher than the CNT-Cu region. The resulting composite was found to have specific conductivity similar to that of pure copper i.e. 98% of copper with 0.2 w-% of CNT, exhibiting a ninefold increase from the pure CNT fiber. Self-annealing was shown to decrease the resistance of the composite.

doi:10.1016/j.carbon.2016.06.008
04/2016
Effect of compression on the electronic, optical and transport properties of MoS2/graphene-based junctions 2D Mater. 3 (2016) 025018
M. Ghorbani-Asl, P.D. Bristowe, K. Koziol, T. Heine and A. Kuc

Electrochemical deposition of copper on a carbon nanotube (CNT) fiber from a copper sulfate – sulfuric acid bath was studied in order to produce a carbon nanotube-copper composite wire. The high resistivity of the aerogel-spun fiber causes a non-uniform current distribution during deposition, which results in a drastic drop in the copper nuclei population density as sufficient overpotential is not available beyond a certain distance from the current feed point. Copper was found to fill the pores between CNT bundles from Focused Ion Beam (FIB) cut cross-sections confirming that aqueous based electrolytes can fill micropores between as-spun CNTs in a fiber network. The speed at which copper grows on the fiber surface was identified at ca. 0.08 mm/s with 1 mA applied current. The copper cladding showed columnar growth with a grain size an order of magnitude higher than the CNT-Cu region. The resulting composite was found to have specific conductivity similar to that of pure copper i.e. 98% of copper with 0.2 w-% of CNT, exhibiting a ninefold increase from the pure CNT fiber. Self-annealing was shown to decrease the resistance of the composite.

doi:10.1016/j.carbon.2016.06.008
03/2016
Chitin and carbon nanotube composites as biocompatible scaffolds for neuron growthNanoscale, 2016,8, 8288-8299
N. Singh, J. Chen, K. Koziol, K.R. Hallam, D. Janas, A.J. Patil, A. Strachan, J.G. Hanley and S.S. Rahatekar

The design of biocompatible implants for neuron repair/regeneration ideally requires high cell adhesion as well as good electrical conductivity.  Here, we have shown that plasma treated chitin carbon nanotube composite scaffolds show very good neuron adhesion as well as support of synaptic function of neurons.  The addition of carbon nanotubes to a chitin bipolymer improved the electrical conductivity and the assisted oxygen plasma treatment introduced more oxygen species onto the chitin carbon nanotube scaffold surface.  Neuron viability experiments showed excellent neuron attachment onto plasma-treated chitin nanotube composite scaffolds.  The support of synaptic function was evident on chitin/nanotube composites, as confirmed by PSD-95 staining.  The biocompatible and electrically conducting chitin nanotube composite scaffold prepared in this study can be used for in vitro tissue engineering of neurons and, potentially, as an implantable electrode for stimulation and repair of neurons.

DOI: 10.1039/C5NR06595J