Carbon nanotubes (CNTs) have specific physico-chemical and electrical properties that are useful for telecommunications, medicine, materials, manufacturing processes and the environmental and energy sectors. Yet, despite their many advantages, it is also important to determine whether CNTs may represent a hazard to the environment and human health. Like asbestos, the aspect ratio (length:diameter) and metal components of CNTs are known to have an effect on the toxicity of carbon nanotubes. Thus, to evaluate the toxic potential of CNTs in relation to their aspect ratio and metal contamination, in vivo and in vitro genotoxicity tests were conducted using high-aspect-ratio (diameter: 10-15 nm, length: ~10 μm) and low-aspect-ratio multi-wall carbon nanotubes (MWCNTs, diameter: 10-15 nm, length: ~150 nm) according to OECD test guidelines 471 (bacterial reverse mutation test), 473 (in vitro chromosome aberration test), and 474 (in vivo micronuclei test) with a good laboratory practice system. To determine the treatment concentration for all the tests, a solubility and dispersive test was performed, and a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) solution found to be more suitable than distilled water. Neither the high- nor the low-aspect-ratio MWCNTs induced any genotoxicity in a bacterial reverse mutation test (~1,000 μg/plate), in vitro chromosome aberration test (without S9: ~6.25 μg/ml, with S9: ~50 μg/ml), or in vivo micronuclei test (~50 mg/kg). However, the high-aspect-ratio MWCNTs were found to be more toxic than the low-aspect-ratio MWCNTs. Thus, while high-aspect-ratio MWCNTs do not induce direct genotoxicity or metabolic activation-mediated genotoxicity, genotoxicity could still be induced indirectly through oxidative stress or inflammation.

Several single-walled carbon nanotubes (SWCNTs) prepared by different methods have been used to investigate the material dependence on the optimal film performance of flexible transparent conducting films. The nanotubes were dispersed in water with sodium dodecyl sulfate by sonication. These SWCNT solutions were then sprayed onto the Poly(ethylene terephthalate) substrate by a spray coater to form the film. Several factors such as purity, diameter, defects, metallicity, and degree of dispersion were evaluated individually to examine how they affect the film performance. We found that the metallicity of SWCNTs and the degree of dispersion are the most crucial factors in determining the film performance. We also proposed a material quality factor to estimate the material quality of SWCNTs as a figure of merit for the film performance.

The electro-optic response of a carbon nanotube (CNT) cluster has been investigated. The cluster absorbs incident light before stretching. In the presence of an electric field, the cluster starts stretching along the field direction and contracts back to its original stage when the applied voltage is removed. The stretched cluster absorbs and transmits incident light with its electric vector propagating parallel and perpendicular to the long axis of the stretched cluster, respectively. Utilizing this selective light absorption property of a CNT cluster, a tunable polarizer or non-emissive light modulator can be realized.

No abstract

The mechanism of field emission from a metal surface was well explained based on the quantum mechanics in early 20th century. Since then, various materials have been studied for field emitters. However, so far, we have been using only limited materials as a field emitter and an application in some area requires further scientific understandings and technological advancements. In this paper, we review the current status of researches in field emission and emission phenomena of carbon nanotubes (CNTs). This may include current saturation induced by gas adsorbates, screening effects, high current emission, degradation of emitter, and field enhancement factor. We also introduce the present status in the development of various CNT-based field emission devices and discuss their performances. In this part, various potential applications such as field emission display, ionization gauge, X-ray gun, and lamp will be presented. Keywords: Carbon nanotubes; field emission. 69 NANO 2007.02:69-89. Downloaded from www.worldscientific.com by NORTHWESTERN UNIVERSITY on 03/25/15. For personal use only. 70 S. C. Lim et al. NANO 2007.02:69-89. Downloaded from www.worldscientific.com by NORTHWESTERN UNIVERSITY on 03/25/15. For personal use only. Field Emission and Application of Carbon Nanotubes 71 NANO 2007.02:69-89. Downloaded from www.worldscientific.com by NORTHWESTERN UNIVERSITY on 03/25/15. For personal use only. 72 S. C. Lim et al.