Slippage processes

This simulation protocol was employed to study the slippage processes associated with R equal to H, Me, Et and i-Pr. In all cases, the resulting energy profiles displayed two energy barriers. The first of... 

Harrison [4, 33, 34] and later, Schill and coworkers [38] had explored temperature-controlled slippage. Another approach was to control the size of the stoppers by complexation. Stoddart and coworkers [90] could thread macrocycle (27) onto dumbbells ended by aza crown ethers. The slippage process was inhibited by addition of an alkali cation. Conversely, complexation of the aza-crown after the slippage process inhibited unthreading. 

A series of novel (77 -l-azaallyl)-Ni complexes 91 and 92 has been reported recently.The solid-state structures of these complexes confirm the 77 -coordination of the azaallyl ligands (Ni-C 203-206 pm Ni-N 188-192 pm). Variable-temperature NMR studies have shown that 91 and 92 undergo a dynamic process in solution that generates three different isomers, presumably via 77 /7/ -slippage processes. 

Imposition of no-slip velocity conditions at solid walls is based on the assumption that the shear stress at these surfaces always remains below a critical value to allow a complete welting of the wall by the fluid. This iraplie.s that the fluid is constantly sticking to the wall and is moving with a velocity exactly equal to the wall velocity. It is well known that in polymer flow processes the shear stress at the domain walls frequently surpasses the critical threshold and fluid slippage at the solid surfaces occurs. Wall-slip phenomenon is described by Navier s slip condition, which is a relationship between the tangential component of the momentum flux at the wall and the local slip velocity (Sillrman and Scriven, 1980). In a two-dimensional domain this relationship is expressed as... 

The resultant low level of particular salts remaining in a processed water after passing through an ion-exchange plant. Slippage occurs because of a less than totally efficient exchange capability processes. 

In 1991, Cram s research group reported a new class of container molecules, named hemkarcerands 6] that are involved (Figure lc) in several processes related to slippage. Guests can be imprisoned... 

The clipping reaction used in [52, 53, 55] to synthesize tetralactam-based squaraine rotaxanes such as 14 and 15 afforded only moderate yields (ca. 28-35%) of the rotaxanes, possibly because of the unavoidable presence of nucleophiles that react with the chemically unstable squaraines during the reaction. The slippage approach [62] minimizes the squaraine dye s contact with nucleophiles during the rotaxane formation process and therefore can be used to efficiently encapsulate a squaraine dye such as 23 in a macrocycle such as 25 [63],... 

Additionally, it should be observed that the thermal oxidability and oxidative polymerization of the unsaturated fatty acids follows the trend linolenic > linoleic > oleic > > palmitoleic (Martinenghi, 1963). The oxidation involves, as first step, the abstraction of a hydrogen atom in allylic position to the double bonds. Certainly, this process is favoured in the case of fatty acids with two or more unconjugated double bonds where the formation of a free radical by allylic hydrogen abstraction leads quite necessarily to double bonds slippage with formation of conjugated double bonds ... 

The introduction of cross-links to inhibit chain slippage was discovered by Goodyear in 1839. He accomplished this through the addition of sulfur to NR. Shortly after this, an accelerator, zinc (II) oxide, was used to speed up the process. Other additives were discovered often through observation and trial-and-error so that today s elastomers have a number of important additives that allow them to perform demanding tasks. 

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