Requiring Chemical Reaction Before Application

Dves Requiring Chemical Reaction before Application 

Both vat and sulfur dyes must be chemically reduced before application to a fiber, whereas azoic or naphthol dyes are formed through reaction of two separate dye components after appl ication to the fiber. These dyes tend to penetrate the fiber less than other dyes, and care must be exercised in application to get reasonable fastness properties. 

Vat Dves Vat dyes are usually water-insoluble dyes that can be chemically reduced in the presence of base to form a water-soluble and colorless leuco form of the dye, which is then appl ied to the fiber. Vat dyes can be 

The dyes are usually indigoids (such as indigo) or anthraquinone derivatives and applied at low (30° 60°) temperatures. After application of the leuco form of the vat dye, the dye is reoxidized on the fabric by oxygen in the air or through treatment of the dyed fabric with a mild oxidizing agent. The vat dyes are reasonably colorfast if poorly held surface dye has been removed  

Stable sul fate esters of reduced leuco forms of vat dyes are available which do not require prior chemical reduction before application. 

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Dyes Requiring Chemical Reaction before Application Vat dyes Azoic dyes Sul fur dyes... 

Dves Requiring Chemical Reaction before Application... 

For trace analysis in fluids, some Raman sensors (try to) make use of the SERS effect to increase their sensitivity. While the basic sensor layout for SERS sensors is similar to non-enhanced Raman sensors, somehow the metal particles have to be added. Other than in the laboratory, where the necessary metal particles can be added as colloidal solution to the sample, for sensor applications the particles must be suitably immobilised. In most cases, this is achieved by depositing the metal particles onto the surfaces of the excitation waveguide or the interface window and covering them with a suitable protection layer. The additional layer is required as otherwise washout effects or chemical reactions between e.g. sulphur-compounds and the particles reduce the enhancement effect. Alternatively, it is also possible to disperse the metal particles in the layer material before coating and apply them in one step with the coating. Suitable protection or matrix materials for SERS substrates could be e.g. sol-gel layers or polymer coatings. In either... 

In many reacting flows, the reactants are introduced into the reactor with an integral scale L that is significantly different from the turbulence integral scale Lu. For example, in a CSTR, Lu is determined primarily by the actions of the impeller. However, is fixed by the feed tube diameter and feed flow rate. Thus, near the feed point the scalar energy spectrum will not be in equilibrium with the velocity spectrum. A relaxation period of duration on the order of xu is required before equilibrium is attained. In a reacting flow, because the relaxation period is relatively long, most of the fast chemical reactions can occur before the equilibrium model, (4.93), is applicable. 

The first question is how such a bubble can be formed, considering the fact that the forces required to separate water molecules to a distance of two van-der Waals radii, would require a power of 10 W cm [4]. On the other hand, it is well known that in a sonication bath, with a power of 0.3 W cm [4] water is already converted into hydrogen peroxide. Different explanations have been offered they are all based on the existence of unseen particles, or gas bubbles, that decrease the intermolecular forces, enabling the creation of the bubble. The experimental evidence for the importance of unseen particles in sonochemistry is that when the solution undergoes ultrafiltration, before the application of the ultrasonic power, there is no chemical reaction and chemical bonds are not ruptured. 

Quite aside from physical or chemical reactions, an important function served by high vacuum is the provision of collision-free space, such as required in radio and television tubes, and particle accelerators. In these applications, charged particles must travel relatively long distances before reaching their target. Obviously, their path will be unimpeded only when the probability of collision with residual gas molecules is very low. A similar function is served in vacuum coating, where metal vapor is condensed on a suitable substrate some distance from an evaporation source. 

The second means of transforming a liquid adhesive entirely into a solid without the loss of a solvent or dispersion medium is to produce solidification by a chemical change rather than a physical one. Such reactive adhesives may be single-part materials that generally require heating or exposure to electron beam or UV or visible radiation (see Radiation-cured adhesives) to perform the reaction, and which may be solids (that must be melted before application), liquids or pastes. The alternative two-part systems require the reactants to be stored separately and mixed only shortly before application. The former class is exemplified by the fusible, but ultimately reactive, epoxide film adhesives and the latter by the two-pack Epoxide adhesives and Polyurethane adhesives and by the Toughened acrylic adhesives that cure by a free-radical Chain polymerization mechanism. 

Excited-states simulations were mainly limited to small and medium-sized molecules before the 90s. However, many important photophysical processes, as for example, the photoisomerization of rhodopsin, take place in a biological environment, seldom not without the presence of an enzyme. To study photochemical processes in the large-size systems, alternative methods are required. One such method, the QM/MM method," was developed by Warshel and Levitt in 1976. This approach combines the accuracy of quantum chemical models with the speed of molecular mechanics. An alternative method to combine different quantum chemical approaches, the ONIOM method, was developed by Morokuma and co-workers." These methods were initially used in the context of ground-state reactions. Early applications of the QM/MM hybrid method to photochemical processes can be found as early as 1982," however, it was not until at the beginning of this century that the method started to be used extensively for photochemical and photophysical dynamics. To find representative investigations of that time consult the reference list." " ... 

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