Carbon Nanotubes and Graphene - Research and Applications

Polyaniline-coated multi-wall carbon nanotubes (PANI-coated MWNTs) were prepared by in situ polymerization method. Field emission scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and thermogravimetric analysis were used to characterize the as-prepared PANI-coated MWNTs. Obtained results indicated that PANI was uniformly coated on MWNTs, and the thickness of the coatings can be controlled by changing the weight ratios of aniline monomer and MWNTs in the polymerization process. Sensors were fabricated by spin-coating onto pre-patterned electrodes, and ammonia gas sensing properties of the as-prepared PANI-coated MWNTs were studied. The results showed a good response and reproducibility towards ammonia at room temperature. In addition, PANI-coated MWNTs exhibited a linear response to ammonia in the range of 0.2–15 ppm. The effects of the thickness of PANI coatings on the gas sensing properties were also investigated in detail. The results suggest a potential application of PANI-coated MWNTs in gas sensor for detecting ammonia.

(Lifang He, Yong Jia, Fanli Meng, Minqiang Li, and Jinhuai Liu, Materials Science and Engineering: B 163, Issue 2, 15 July 2009, Pages 76-81, doi:10.1016/j.mseb.2009.05.009)

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 Fe₂O₃ itself yielded toxicity only from the nanotubes and not from the Fe₂O₃. 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.

(Crystal Cheng, Karin H. Müller, Krzysztof K.K. Koziol, Jeremy N. Skepper, Paul A. Midgley, Mark E. Welland, and Alexandra E. Porter, Biomaterials 30, Issue 25, September 2009, Pages 4152-4160, doi:10.1016/j.biomaterials.2009.04.019)

Multifunctional nanocomposites are increasingly needed for applications requiring prescribed sets of physical and chemical properties. Polytetrafluoroethylene (PTFE) is a popular solid lubricant due to its low friction coefficient, high chemical inertness, high thermal range and biocompatibility, but its use is limited by high rates of wear. Low loadings of nanoparticle fillers have reduced PTFE wear by 3–4 orders of magnitude, but these materials lack the mechanical, electrical or thermal properties needed for high performance applications.

In this study, single-walled carbon nanotubes (SWCNT) are investigated as a route to improve wear resistance, toughness and electrical conductivity of PTFE without sacrificing low friction, high temperature capability or chemical inertness. Tribological, tensile and surface electrical measurements were made for 0, 2, 5, 10 and 15 wt.% SWCNT filled PTFE nanocomposites. A dramatic reduction in electrical resistance reflected networking (percolation) of the nanotubes at 2 wt.%. All of the nanocomposites had significantly improved electrical, mechanical and wear performance. Above 2 wt.%, electrical conductivity was reduced by more than six orders of magnitude. At 2 wt.%, ultimate engineering stress was improved by approximately 50%, true stress increased by 200%, engineering strain increased by two orders of magnitude (10,000%). At 5 wt.%, wear resistance improved by more than 20 times and friction coefficient increased by 50%.
(J.R. Vail, D.L. Burris, and W.G. Sawyer, Wear 267, Issues 1-4, 15 June 2009, Pages 619-624, doi:10.1016/j.wear.2008.12.117)