Stable immiscibility

Figrue 4.5 Idealized phase diagram for a binary system exhibiting stable immiscibility... 

Similar trends exist for many other systems. In general, the critical temperature within series such as the alkaline earth silicates or borates will decrease with increasing radius of the alkaline earth cation. In the former case, the suppression of the critical temperature with increasing radius of the alkaline earth cation is great enough that barium silicate melts exhibit metastable immiscibility, while the other alkaline earth silicates exhibit stable immiscibility. 

Phase separation can radically alter the viscosity of a melt. If stable immiscibility leads to complete separation into two layers of liquid,... 

These results confirm the earlier conclusion [18] that at 26 5mol% P2O5 there is a stable immiscibility in Te02 P205 glasses, combination of SANS and TOP methods is very powerful. The use of pulsed neutron sources and position sensitive detectors permits the construction of a TOP apparatus at A / >0.1 with performances, compatible to or better than the best x-ray small angle scattering instruments. 

The T-X scheme IIIj3-3 (Figure 1.36) clearly shows that the metastable immiscibility region spreading from the binary subsystem A-C of type 2 can transform into the stable equilibria, and how the stable immiscibility region, spreading from the binary subsystem A-B of type Id, transforms into the metastable equilibria as a result of intersection with a crystallization surface. 

Liquid-liquid immiscibility in silicates. (A) Stable immiscibility (above the liquidus) in the alkaline earth silicate systems. (B) Metastable immiscibility in the Na20-Si02 system. From Seward [16]. 

If two pure, immiscible liquids, such as benzene and water, are vigorously shaken together, they will form a dispersion, but it is doubtful that one phase or the other will be uniquely continuous or dispersed. On stopping the agitation, phase separation occurs so quickly that it is questionable whether the term emulsion really should be applied to the system. A surfactant component is generally needed to obtain a stable or reasonably stable emulsion. Thus, if a little soap is added to the benzene-water system, the result on shaking is a true emulsion that separates out only very slowly. Theories of... 

Discuss briefly at least two reasons why two pure immiscible liquids do not form a stable emulsion. 

Although, for most moderators, the surface of a stationary phase in LC can be considered stable at moderator concentrations above about 5%v/v, the results from the same experiments as those carried out by Purnell and his group could still be considered invalid and, at best, would not lead to unambiguous conclusions. Katz et al. [9] avoided this problem by examining liquid/liquid distribution systems using water as one phase and a series of immiscible solvent mixtures as the other and by measuring absolute distribution coefficients as opposed to retention volumes. 

Room temperature ionic liquids are air stable, non-flammable, nonexplosive, immiscible with many Diels-Alder components and adducts, do not evaporate easily and act as support for the catalyst. They are useful solvents, especially for moisture and oxygen-sensitive reactants and products. In addition they are easy to handle, can be used in a large thermal range (typically —40 °C to 200 °C) and can be recovered and reused. This last point is particularly important when ionic liquids are used for catalytic reactions. The reactions are carried out under biphasic conditions and the products can be isolated by decanting the organic layer. 

In micro reactors, large specific interfaces between immiscible phases can in general be achieved. In special laminating contactors, a stable two-phase flow with continuous phases can be obtained, while separation of the phases is facilitated when the two separate streams leave the micro reactor as there is no dispersion. 

Emulsions are stable dispersions of two immiscible liquids. In the aluminum forming category this is usually an oil and water mixture. 

Why does the minor component in an immiscible blend prefer to form spherical morphologies in the absence of applied stresses How do the less stable shapes of rods or platelets form ... 

An emulsion is a dispersed system of two immiscible phases. Emulsions are present in several food systems. In general, the disperse phase in an emulsion is normally in globules 0.1-10 microns in diameter. Emulsions are commonly classed as either oil in water (O/W) or water in oil (W/O). In sugar confectionery, O/W emulsions are most usually encountered, or perhaps more accurately, oil in sugar syrup. One of the most important properties of an emulsion is its stability, normally referred to as its emulsion stability. Emulsions normally break by one of three processes creaming (or sedimentation), flocculation or droplet coalescence. Creaming and sedimentation originate in density differences between the two phases. Emulsions often break by a mixture of the processes. The time it takes for an emulsion to break can vary from seconds to years. Emulsions are not normally inherently stable since they are not a thermodynamic state of matter. A stable emulsion normally needs some material to make the emulsion stable. Food law complicates this issue since various substances are listed as emulsifiers and stabilisers. Unfortunately, some natural substances that are extremely effective as emulsifiers in practice are not emulsifiers in law. An examination of those materials that do stabilise emulsions allows them to be classified as follows ... 

The standard ruthenium arene and CATHy catalysts are insoluble in water, but are nevertheless stable in the presence of water. Reactions in the I PA system can be carried out in mixtures of isopropanol and water the net effect is a lower rate due to dilution of the hydrogen donor. The use of formate salts in water, with CATHy or other transfer hydrogenation catalysts dissolved in a second immiscible phase was shown to work well with a number of substrates and in some cases to improved reaction rates [34]. The use of water as reaction solvent will be discussed in more detail in Section 35.5. 

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