Positional control, CNTs

Fig. 9.5 Induction of THP-1 cells by 220-CNTs and 825-CNTs. The diacylated lipopeptide FSL-1 was used as a positive control (Gong et al., 2000. With permission from The Royal Society of Chemistry)...

Various positional control techniques exist. Many require time-consuming nanomanipulators operated by skiUed individuals who accurately position individual, previously grown CNTs [221,222]. By combining PE-CVD with mass production facilitated by parallelized lithographic techniques, many millions of CNTs can be simultaneously grown, positioned, and even aligned with extremely high accuracy. 

Negatively charged species such as carboxylic acid group in acid-treated CNTs can attract positively charged enzymes from solution as long as the pH value of the enzyme solution is controlled to be lower than the iso-electric point of the enzyme thus, multilayer films of the enzyme can be formed by the layer-by-layer technique. For example, five layers of GOx can be immobilized on the electrode surface by alternatively dipping a poly(diallyldimethylammonium chloride (PDDA))-functionalized GC into a CNT solution and a GOx solution (pH 3.8). Figure 15.15 illustrates the preparation process for the formation of a multilayer film of GOx on the electrode. 

Double-walled carbon nanotubes (DWNTs), first observed in 1996, constitute a unique family of carbon nanotubes (CNTs). -2 DWNTs occupy a position between the single-walled carbon nanotubes (SWNTs) and the multiwalled carbon nanotubes (MWNTs), as they consist of two concentric cylinders of rolled graphene. DWNTs possess useful electrical and mechanical properties with potential applications. Thus, DWNTs and SWNTs have similar threshold voltages in field electron emission, but the DWNTs exhibit longer lifetimes.3 Unlike SWNTs, which get modified structurally and electronically upon functionalization, chemical functionalization of DWNTs surfaces would lead to novel carbon nanotube materials where the inner tubes are intact. The stability of DWNTs is controlled by the spacing of the inner and outer layers but not by the chirality of the tubes 4 therefore, one obtains a mixture of DWNTs with varying diameters and chirality indices of the inner and outer tubes. DWNTs have been prepared by several techniques, such as arc discharge5 and chemical vapor depo-... 

In the S3mimetric capacitor in which both electrodes are built from the same Mn02/CNT composite, the working potential of positive and negative electrode cannot be controlled. Taking into account the possibility of irreversible transformation of Mn(lV) into... 

In the last few years, great advances have been made regarding SWCNTs separation, based on metallicity. Positive developments were made in controlling and optimizing the generation of CNTs, as well as its separation and purification via chirality and metallicity (Hongjie et al. 2002 Rodney et al. 2002). Therefore, SWCNTs were formed as a small amount of metal particle placed on a dimple... 

In turn, the realization of controlled placement of a SWCNT monolayer network at four different positions in polymer-C60 BHJ solar cells was demonstrated, and their optoelectronic performance was investigated. Several devices were fabricated by precisely placing SWCNTs at different hierarchical levels in the device with structure P3HT/PEDOT/ITO. Dip-coating from an additive-free suspension of mildly purified SWCNTs in DMF was utilized for this purpose. It was found that SWCNTs on the cathodic side of the active layer lead to increased PCE from 4 to 4.9% under AM 1.5 G illumination this being the highest value achieved for polymer-based solar cells incorporating CNTs [51]. 

In practice, although it is seldom clearly stated, all parameters [such as glass ware type, surfactant-CNT dispersion volume, position of the sonicator tip in the sample or sample location in a bath sonicator, etc.] need to be kept fixed for optimum control and reproducibilityofdebundlingexperiments [providedthecomposition of the CNT batch used remains homogeneous]. Additionally, Mason and Lorlmer calculated that any experiment should be carried out at the lowest possible temperature in order to get maximum sonochemlcal benefit. Controlling the temperature is crucial since the surfactant-CNT dispersion heats up during the sonication, which... 

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