Peeling off mechanism

Scheme 3.5 Peeling-off mechanism proposed for the formation of l-amino-l,4-dideoxy-hexosone from an oligosaccharide, such as maltose165...

Hollnagel, A., Kroh, L. W. Degradation of Oligosaccharides in Nonenzymatic Browning by Formation of a-Dicarbonyl Compounds via a "Peeling Off" Mechanism. J. Agric. Food Chem. 2000,48, 6219-6226. 

A. Hollnagel and L. W. Kroh, Degradation of oligosaccharides in nonenzymatic browning by formation of a-dicarbonyl compounds via a peeling off mechanism, J. Agric. Food Chem., 48 (2000) 6219-6226. 

The filter usually has an endless cloth, traveling intermittently between the plates via roUers, to peel off cakes. Unfortunately, if the cloth is damaged anywhere, the whole cloth must be replaced, which is a difficult process. Each time the filter cloth zigzags through the filter, the filtering direction is reversed this tends to keep the cloth clean. Most of these filters incorporate membranes for mechanical expression, and cakes sometimes stick to the membranes and remain in the chamber after discharge. Some vertical filters are available with a separate cloth for each frame. The cloths maybe disposable and such filters are designed to operate with or without filter aids. 

Fracture mechanics (qv) affect adhesion. Fractures can result from imperfections in a coating film which act to concentrate stresses. In some cases, stress concentration results in the propagation of a crack through the film, leading to cohesive failure with less total stress appHcation. Propagating cracks can proceed to the coating/substrate interface, then the coating may peel off the interface, which may require much less force than a normal force pull would require. 

If one considers the hydration of the hydroxide and remembers that the hydroxide once it goes into an activated complex has to peel off its water of hydration, a completely different picture emerges. We looked at the reactivity of the hydroxide in the bimolecular base-catalyzed substitutions both in the case of chloramine and of ethyl iodide (7, 8). Investigating these systems in concentrated hydroxide solutions and calculating the concentration of the so called free hydroxide ions shows that the hydroxide ion is much more reactive than its form in dilute solution. This means, in the kind of sticky mechanisms where you introduce the hydroxide into the complex, it is likely to be much less reactive than one expects from such a strong base. 

Parylene C film does not adhere well to any smooth surface due to its unique polymerization mechanisms as described in Chapter 5. A freestanding film can be easily peeled off of the substrate surface, although a film does not peel off by itself in many cases, even if immersed in water. This feature enables us to investigate a system... 

FIGURE 22.4 Naturally occurring muscovite mica. The mechanical properties of crystals of mica are quite anisotropic. Thin sheets can be peeled off a crystal of mica by hand, but the sheets resist stresses in other directions more strongly. Transparent, thin sheets of mica, sometimes called isinglass, have been used for heat-resistant windows in stoves or in place of window glass. 

In most synthesis processes it is not possible to produce the thin separation layer directly on top of a support with large pores because the precursor system from which the separation layer is made will significantly penetrate the supporting pores (e.g. small particles from which small-pore membranes are made will penetrate much larger pores). This will result in a strongly increasing flow resistance. Furthermore, thin layers covering wide pores are mechanically unstable and wiU crack or peel off easily. 

Usually, the mechanical strength of raw S-SBR is lower than that of E-SBR it is necessary to reduce the distance between two rolls by 10-20% to avoid the peeling off of the roll. On the other hand, S-SBR bonds easily on the cold roll. It will be better to ensure that the temperature difference between two rolls is about 5-10°C during the processing of S-SBR. 

We have argued that STM experiments allow unparalleled structural control, but it is very difficult, if not impossible, to provide a third electrode besides tip and sample that is sufficiently close to the molecular wire. However, it is possible to use the manipulation capability of the STM to achieve a mechanical gating of the molecular wire [31]. The idea of this experiment is shown in Figure 12.12c. By retracting the tip from the surface, the wire junction is stretched and the molecule is peeled off the surface as a consequence. In this way, it is in fact possible to pull individual molecules into an upright orientation and even remove them from the surface. The detailed analysis of the experimental retraction spectra and first principle DFT simulations of the tip retraction process confirms this scenario. 

The details of thin-film formation by PVD or CVD on the atomic and molecular scale are unknown in most cases, but such knowledge would be very helpful to design new processes and to tailor film properties. Information is lacking due to the high reactivities, short lifetimes, and low concentrations of the relevant transient gas-phase species. Furthermore, many of the thin-film properties in statu nascendi are unknown due to the experimental difficulties of thin-film characterization during deposition, particularly with non-crystalline films and if established methods such as RHEED and FEED cannot be applied. Among the film properties, mechanical stress in thin films can lead to unwanted (uncontrolled) instabilities and peel-off phenomena. Therefore, in situ diagnostic methods have been developed to... 

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