Krzysztof Koziol

High-Performance Carbon Nanotube Fiber

With their impressive individual properties, carbon nanotubes should form high-performance fibers. We explored the roles of nanotube length and structure, fiber density, and nanotube orientation in achieving optimum mechanical properties. We found that carbon nanotube fiber, spun directly and continuously from gas phase as an aerogel, combines high strength and high stiffness (axial elastic modulus), with an energy to breakage (toughness) considerably greater than that of any commercial high-strength fiber. Different levels of carbon nanotube orientation, fiber density, and mechanical properties can be achieved by drawing the aerogel at various winding rates. The mechanical data obtained demonstrate the considerable potential of carbon nanotube assemblies in the quest for maximal mechanical performance. The statistical aspects of the mechanical data reveal the deleterious effect of defects and indicate strategies for future work.

Toxicity and imaging of multi-walled carbon nanotubes in human macrophage cells.

Multi-walled carbon nanotubes (MWNTs) have been proposed for use in many applications and concerns about their potential effect on human health have led to the interest in understanding the interactions between MWNTs and human cells. One important technique is the visualisation of the intracellular distribution of MWNTs. We exposed human macrophage cells to unpurified MWNTs and found that a decrease in cell viability was correlated with uptake of MWNTs due to mainly necrosis. Cells treated with purified MWNTs and the main contaminant Fe(2)O(3) itself yielded toxicity only from the nanotubes and not from the Fe(2)O(3). We used 3-D dark-field scanning transmission electron microscopy (DF-STEM) tomography of freeze-dried whole cells as well as confocal and scanning electron microscopy (SEM) to image the cellular uptake and distribution of unpurified MWNTs. We observed that unpurified MWNTs entered the cell both actively and passively frequently inserting through the plasma membrane into the cytoplasm and the nucleus. These suggest that MWNTs may cause incomplete phagocytosis or mechanically pierce through the plasma membrane and result in oxidative stress and cell death.

Optical microstructure and viscosity enhancement for an epoxy resin matrix containing multiwall carbon nanotubes

This paper describes rheological measurements and associated optical microstructural observations of multiwall carbon nanotubes (MWCNTs) suspended in an epoxy resin matrix. The base epoxy resin was found to be essentially Newtonian, and the progressive incorporation of nanotubes enhanced the low shear rate viscosity of the suspension by nearly two decades. At higher shear rates, the suspension viscosity asymptotically thinned to the viscosity of the matrix alone. The low shear rate viscosity enhancement was correlated with the optical observations of interconnected aggregates of carbon nanotubes, which themselves were induced by the low shear conditions. Intermediate shear rates resulted in a reduction in the size of the aggregates. High shear rates appeared to cause near-complete dispersal of the aggregates. From these results it is conjectured that for this suspension, shear thinning is connected with the breaking of the interconnected networks between nanotubes and or aggregates of nanotubes, and not b...

Towards the production of large-scale aligned carbon nanotubes

A novel method is presented to produce high purity, aligned multi-walled carbon nanotube films grown on thin quartz flakes by injecting a solution of ferrocene in toluene. After reaction, these quartz flakes support arrays of nanotubes arranged perpendicular to the surfaces of the substrate. This method is seen to increase the yield of nanotubes dramatically compared to the conventional injection CVD method. Such a method may offer the possibility of producing aligned nanotubes at large scales. In addition, the analysis established the presence of bands of varying iron concentration within this type of material.

Macroscopic fibers of well-aligned carbon nanotubes by wet spinning.

A simple process to spin fibers consisting of multi-walled carbon nanotubes (CNTs) directly from their lyotropic liquid-crystalline phase is reported. Ethylene glycol is used as the lyotropic solvent, enabling a wider range of CNT types to be spun than previously. Fibers spun with CNTs and nitrogen-doped CNTs are compared. X-ray analysis reveals that nitrogen-doped CNTs have a misalignment of only +/-7.8 degrees to the fiber axis. The tensile strength of the CNT and nitrogen-doped CNT fibers is comparable but the modulus and electrical conductivity of the are lower. The electrical conductivity of both types of CNT fibers is found to be highly anisotropic. The results are discussed in context of the microstructure of the CNTs and fibers.

Enhancement of the mechanical properties of directly spun CNT fibers by chemical treatment.

Translating the remarkable mechanical properties of individual carbon nanotubes to macroscopic assemblies presents a unique challenge in maximizing the potential of these remarkable entities for new materials. Infinitely long individual nanotubes would represent the ideal molecular building blocks; however, in the case of length-limited nanotubes, typically in the range of micro- and millimeters, an alternative strategy could be based on the improvement of the mechanical coherency between bundles assembling the macroscopic materials, like fibers or films. Here, we present a method to enhance the mechanical performance of fibers continuously spun from a CVD reactor, by a postproduction processing methodology utilizing a chemical agent aided by UV irradiation. The treatment results in an increase of 100% in specific strength and 300% in toughness of the fibers with strength values rocketing to as high as 3.5 GPa SG(-1). An attempt has been made to explore the nature of the chemical modifications introduced in the fiber and the consequential effects on its properties.

Continuous Direct Spinning of Fibers of Single‐Walled Carbon Nanotubes with Metallic Chirality

The continuing momentum of carbon nanotube research is driven by a number of unresolved issues, particularly those associated with high-temperature synthesis, but also by the challenge of translating the exciting physical properties of the individual nanotubes into useful materials with new properties and applications. A process by which carbon nanotube fi bers can be spun directly from the chemical vapor deposition (CVD) reaction zone was fi rst reported in 2004. [ 1 ] The fi ber formed consisted of comparatively large diameter ( ≈ 7 nm) double-walled nanotubes that collapse to form stacks of graphene-like layers. [ 2 ] Also shown was the potential for exceptional axial mechanical properties. [ 3 , 4 ] The addition of sulfur in the right proportion is key to the formation of a cloud of entangled nanotubes that have suffi cient mechanical integrity to be drawn out of the reactor as a continuous fi ber. The major role of the sulfur has been seen as a “promoter” as suggested much earlier by Kiang et al. [ 5 , 6 ] In the continuous spinning process, sulfur has been identifi ed as segregating to the surface of the iron catalyst particles and the interface between the particle and the nanotube, [ 7 ] an effect recently simulated using molecular dynamics for Mo–S [ 8 ] and since confi rmed for Fe–S, [ 9 ] yet well known in the literature on cast irons. [ 10 ] The nanotubes produced by the process are exceptionally long, some 100 000 times their diameter, and their growth to this length over a few seconds at 1200 ° C seems associated with the promoting effect of added sulfur. Here we report the observation that if the sulfur is made available soon after the ferrocene is fi rst cracked to nucleate the fl oating iron catalyst particles, then it retards the growth of the particles so they nucleate single-walled nanotubes, which are then extracted as continuous ≈ 10 μ m diameter fi ber. Additionally, the fact that armchair (and thus metallic) nanotubes are dominant in the fi ber is surprising and adds further piquancy to their potential applicability. The process is described in Figure S1 (Supporting Information). We note (Supporting Information, Table S1) that the window of composition ratios for successful spinning is centred on Fe/C 0.008, the same as for successful spinning from thiophene, but the required Fe/S ratio is 0.080 for thiophene compared with 0.006 for the carbon disulfi de. Furthermore, the results provide additional input to the on-going debate as to the source of chirality preference in as-grown SWNTs [ 11–14 ] and is discussed in the context of three specifi c models: imprinting catalyst structure, [ 15 , 16 ] cap control of chirality, [ 17 , 18 ] and dislocation models of nanotube growth and reorientation. [ 18–20 ]

Polystyrene grafted multi-walled carbon nanotubes

Oxidised, multi-walled, carbon nanotubes can be grafted with polystyrene molecules using an situ radical polymerisation reaction, thereby dramatically modifying their solubility and their suitability for nanocomposite applications.

Three-dimensional carbon nanowall structures

The authors report the growth of carbon nanowalls in freestanding, three-dimensional aggregates by microwave plasma-enhanced chemical vapor deposition. Carbon nanowalls extrude from plasma sites into three-dimensional space. The growth is catalyst-free and not limited by nucleating surfaces. The growth mechanism is discussed and compared with similar carbon nanomaterials. High surface area of as-grown carbon nanowalls indicates a potential for electrochemical applications. Field emission measurements show a low field turn-on and long-term stability. The results establish a scalable production method and possible applications using field emission or high surface area.

Growth of high-quality single-wall carbon nanotubes without amorphous carbon formation

We report an alternative way of preparing high-quality single-wall carbon nanotubes (SWCNTs). Using a triple-layer thin film of Al/Fe/Mo (with Fe as a catalyst) on an oxidized Si substrate, the sample is exposed to a single short burst (5 s) of acetylene at 1000 °C. This produced a high yield of very well graphitized SWCNTs, as confirmed by transmission electron microscopy and Raman spectroscopy. We believe that the high temperature is responsible for the high crystallinity/straightness of the nanotubes, and the rapid growth process allows us to achieve a clean amorphous carbon (a-C) free deposition which is important for SWCNT device fabrication. The absence of a-C is confirmed by Auger electron spectroscopy, Raman spectroscopy, and electrical measurements.