Immiscible process class

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 ... 

Extraction is the process of transferring a substance from a solid to a liquid phase or from a liquid to another liquid phase (immiscible with the former). From a practical viewpoint, the process can be achieved by leaching, which is transfer of compoimds from a solid phase to a solution (solid-liquid extraction, SEE) or by extraction via direct (liquid-liquid extraction, LEE) or indirect (SPE or solid phase microextraction, SPME) transfer of a substance from one liquid phase to another [75]. The efficiency of the extraction process is expressed as the percentage of extraction, which takes into accoimt the affinity of the investigated compoimds for both phases. In practice, a commonly used concept is that of recovery, understood as the degree of transition of a substance from one phase to another, expressed as a percentage. There are multiple methods for determining recovery. They can be divided into two classes ... 

Polymer nanocomposites and polymer blends are an extremely important class of materials due to the expected synergistic enhancement of properties and potential multi-functionality. However, the immiscibility of most of the polymers results in poor interfacial interaction between the individual components which severely affects the hnal properties. A deeper insight into the spatial heterogeneity and morphology of the individual components at a microscopic level and their inhuence on the macroscopic properties is important for their rational design (such as choice and volume fraction of individual components, surface chemistry, and processing... 

The majority of commercially important, immiscible polymer blends rely for compatibilization on the presence of a copolymer of the blended polymers. Nowadays, such a copolymer is almost never synthesized in a separate step and then added as a distinct entity to the blend of immiscible polymers. Instead, a compatibUizing copolymer is most economically formed simultaneously with generation of interphase morphology during extrusion processing, a process referred to as Reactive Compatibilization. The Reactive Compatibilization process is logically a sub-category of the broader class of Interchain Copolymer Formation reactions performed by Reactive Extrusion [Brown, 1992],... 

Redox reactions at the interface between immiscible liquids fall into two classes. The first class includes spontaneous processes that occur in the absence of external electromagnetic fields [16-77]. This type of redox transformation has been investigated in bioenergetics, model membrane systems and at oil/water interfaces [78-99]. Redox reactions in the second class occur at the interface between immiscible electrolytes when external electrical fields are applied to the interface, and under these conditions interfacial charge-transfer reactions take place at controlled interfacial potentials [100-139]. 

Analysis of complex mixtures often requires separation and isolation of components, or classes of components. Examples in noninstrumental analysis include extraction, precipitation, and distillation. These procedures partition components between two phases based on differences in the components physical properties. In liquid-liquid extraction components are distributed between two immiscible liquids based on their similarity in polarity to the two liquids (i.e., like dissolves like ). In precipitation, the separation between solid and liquid phases depends on relative solubility in the liquid phase. In distillation the partition between the mixture liquid phase and its vapor (prior to recondensation of the separated vapor) is primarily governed by the relative vapor pressures of the components at different temperatures (i.e., differences in boiling points). When the relevant physical properties of the two components are very similar, their distribution between the phases at equilibrium will result in shght enrichment of each in one of the phases, rather than complete separation. To attain nearly complete separation the partition process must be repeated multiple times, and the partially separated fractions recombined and repartitioned multiple times in a carefully organized fashion. This is achieved in the laborious batch processes of countercurrent liquid—liquid extraction, fractional crystallization, and fractional distillation. The latter appears to operate continuously, as the vapors from a single equilibration chamber are drawn off and recondensed, but the equilibration in each of the chambers or plates of a fractional distillation tower represents a discrete equihbration at a characteristic temperature. 

An emulsion has been defined above as a thermodynamically unstable heterogeneous system of two immiscible liquids where one is dispersed in the other. There are two principal possibilities for preparing emulsions the destruction of a larger volume into smaller sub-units (comminution method) or the construction of emulsion droplets from smaller units (condensation method). Both methods are of technical importance for the preparation of emulsions for polymerization processes and will be discussed in more detail below. To impart a certain degree of kinetic stability to emulsions, different additives are employed which have to fulfil special demands in the particular applications. The most important class of such additives, which are also called emulsifying agents, are surface-active and hence influence the interfacial properties. In particular, they have to counteract the rapid coalescence of the droplets caused by the van der Waals attraction forces. In the polymerization sense, these additives can be roughly subdivided into surfactants for emulsion polymerization, polymers for suspension and dispersion polymerization, finely dispersed insoluble particles (also for suspension polymerization), and combinations thereof (cf. below). 

So the rinsing mechanism in aU Class II cosolvent processes is displacement — because the two fluids are immiscible. A significant difference in density (>0.15 to 0.25 g/cc) between... 

The highest value of Ra, relative to the chosen SA cosolvent, ensures the greatest immiscibility between the chosen SA and the to-be-chosen (from Table 3.2) RA cosolvent. Fora Class II cosolvent process, one wants the chosen SA and RA cosolvents to most effidently and effectively separate from one another in the rinse sump - representing the highest value of Ra between the SA and the RA. 

Table 3.3 Selection of Cosolvent Pairs with Various Soils for Class II A Cosolvent Processes (Immiscible, Flammable) ... 

Class II A and II B cosolvent processes are foimded on the conventional idea that rinsing in a solvent cleaning process should be done by displacing a low-density solvent with high-density solvent. Both of these solvents are to be immiscible with one another. 

With but a single exception, there are NO circumstances where an RA cosolvent can be chosen to be acceptably immiscible with a suitable SA cosolvent for any Class II cosolvent process. This statement is based on the requirement for acceptability noted in Figure 3.35, that the Ra separation between SA and RA cosolvents be 14 to 16 MPa at a minimum. 

It means that Class II cosolvent processes won t be recognized for providing part surfaces free of the SA cosolvent. This is because the RA cosolvent (the rinse fluid) is not adequately immiscible with (too soluble in) the SA cosolvent. Experientially, these processes aren t recognized for the quality of their rinsing of SA cosolvent by RA cosolvent. 

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