Domino pushing

Another way to produce buckypaper without the dispersion and filtration method is the domino pushing effect . Ding et al present a simple and effective macroscopic manipulation of aligned CNT arrays. The domino pushing of the CNT arrays can efficiently ensure that most of the CNTs are well aligned tightly in the buckypaper structure. 

There are various methods to manufacture carbon nanotube paper. The manufacturing process can be divided into two categories the one-step method and the two-step method. For the two-step method, carbon nanotubes are synthesized first and the paper is made from the nanotubes. In the one-step method, carbon nanotube paper is grown directly. The two-step method is the main process to make carbon nanotube paper, including vacuum/pressure filtration, spin-coating and domino pushing method. 

A simple but effective macroscopic manipulation of carbon nanotube arrays called domino pushing has been developed to make thicker aligned carbon nanotube papers. The schematic of the domino pushing method is shown in Fig. 4.6. First, the nanotube array is covered with a piece of micro-porous membrane. The nanotubes in the array are then... 

Schematic of domino pushing method. (From reference 17.)... 

FIGURE 7.3 Domino pushing of a CNT array to produce high-quality buckypaper. 

Figure 10.3 Schematics of the domino pushing method, (a) Form aligned buckypaper. (b) Peel the buckypaper off the silicon substrate, (c) Peel the buckypaper off the microporous membrane. Reprinted from Ref [47] with permission from lOP Publishing, Copyright 2008.

Formation of 17 can be explained by a domino sequence that begins with an exo-dig cyclization followed by intramolecular trapping of the iminium indole cation by the amide NH to yield 17. The nucleophilic attack of amide on the indole is possible only after the exo-dig addition of the indole to the alkyne from the front side, thus keeping the indole imine in close proximity to the amide. In case of a rear face exo-dig attack, subsequent nucleophilic attack on the iminium is sterically blocked, which pushes the equilibrium of the reaction toward ring opening of intermediate 19 back to the Ugi product 18 (Scheme 13.4). Overall, in this domino process, two new stereogenic centers are formed in a complex tetracyclic molecule. 

In 2007, Chen, Deng, and co-workers [42] reported the first asymmetric domino reaction catalysed by primary amines. A primary amine derived from quinine catalyzed a Michael-Michael-retro-Michael cascade, where the two reagents (64 and 65) act alternatively and selectively as the Michael donor and acceptor under readily controllable conditions. The corresponding cyclohexenones 66 were obtained in good yields and excellent stereoselectivities (Scheme 10.20). However, an extra step was sometimes necessary in order to push the reaction and thus to obtain the cyclic products. In this case, the initial Michael adduct was treated with benzylamine and TEA to render the cycloadduct. 

Volla, C. M. R., Atodiresei, I., Rueping, M. (2013). Catalytic C-C bond-forming multi-component cascade or domino reactions pushing the boundaries of complexity in... 

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