The continuous phase

The viscosity of dispersions is first of aU controlled by the continuous phase liquid which might itself be Newtonian or non-Newtonian, and then the added dispersed phase where the size, shape, amount and deformability of the particles of dispersed material can vary considerably, as can the interaction between the individual dispersed particles. 

For many liquids the continuous phase is Newtonian, and might be water, as found in most household or personal care products, modern paints, etc. On the 

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On a microscopic scale (the inset represents about 1 - 2mm ), even in parts of the reservoir which have been swept by water, some oil remains as residual oil. The surface tension at the oil-water interface is so high that as the water attempts to displace the oil out of the pore space through the small capillaries, the continuous phase of oil breaks up, leaving small droplets of oil (snapped off, or capillary trapped oil) in the pore space. Typical residual oil saturation (S ) is in the range 10-40 % of the pore space, and is higher in tighter sands, where the capillaries are smaller. 

Symmetry considerations forbid any nonzero off-diagonal matrix elements in Eq. (68) when f(x) is even in x, but they can be nonzero if f x) is odd, for example,/(x) = x. (Note that x itself hansforms as B2 [284].) Figure 3 shows the outcome for the phase by the continuous phase tracing method for cycling... 

If a linear mbber is used as a feedstock for the mass process (85), the mbber becomes insoluble in the mixture of monomers and SAN polymer which is formed in the reactors, and discrete mbber particles are formed. This is referred to as phase inversion since the continuous phase shifts from mbber to SAN. Grafting of some of the SAN onto the mbber particles occurs as in the emulsion process. Typically, the mass-produced mbber particles are larger (0.5 to 5 llm) than those of emulsion-based ABS (0.1 to 1 llm) and contain much larger internal occlusions of SAN polymer. The reaction recipe can include polymerization initiators, chain-transfer agents, and other additives. Diluents are sometimes used to reduce the viscosity of the monomer and polymer mixture to faciUtate processing at high conversion. The product from the reactor system is devolatilized to remove the unreacted monomers and is then pelletized. Equipment used for devolatilization includes single- and twin-screw extmders, and flash and thin film evaporators. Unreacted monomers are recovered for recycle to the reactors to improve the process yield. 

The values of k and hence Sb depend on whether the phase under consideration is the continuous phase, c, surrounding the drop, or the dispersed phase, d, comprising the drop. The notations and Sh are used for the respective mass-transfer coefficients and Sherwood numbers. 

Interfacial Contact Area and Approach to Equilibrium. Experimental extraction cells such as the original Lewis stirred cell (52) are often operated with a flat Hquid—Hquid interface the area of which can easily be measured. In the single-drop apparatus, a regular sequence of drops of known diameter is released through the continuous phase (42). These units are useful for the direct calculation of the mass flux N and hence the mass-transfer coefficient for a given system. 

However, in a countercurrent column contactor as sketched in Figure 8, the holdup of the dispersed phase is considerably less than this, because the dispersed drops travel quite fast through the continuous phase and therefore have a relatively short residence time in the equipment. The holdup is related to the superficial velocities U of each phase, defined as the flow rate per unit cross section of the contactor, and to a sHp velocity U (71,72) ... 

The nonuniformity of drop dispersions can often be important in extraction. This nonuniformity can lead to axial variation of holdup in a column even though the flow rates and other conditions are held constant. For example, there is a tendency for the smallest drops to remain in a column longer than the larger ones, and thereby to accumulate and lead to a locali2ed increase in holdup. This phenomenon has been studied in reciprocating-plate columns (74). In the process of drop breakup, extremely small secondary drops are often formed (64). These drops, which may be only a few micrometers in diameter, can become entrained in the continuous phase when leaving the contactor. Entrainment can occur weU below the flooding point. 

The role of coalescence within a contactor is not always obvious. Sometimes the effect of coalescence can be inferred when the holdup is a factor in determining the Sauter mean diameter (67). If mass transfer occurs from the dispersed (d) to the continuous (e) phase, the approach of two drops can lead to the formation of a local surface tension gradient which promotes the drainage of the intervening film of the continuous phase (75) and thereby enhances coalescence. It has been observed that d-X.o-c mass transfer can lead to the formation of much larger drops than for the reverse mass-transfer direction, c to... 

In chocolate, cocoa butter is the continuous phase. The characteristic meltabiUty of cocoa butter constitutes a puzzle in chemical stmcture and poses difficulty in replacement cocoa butter has a sharp melting point at body temperature. 

Another type of polyol often used in the manufacture of flexible polyurethane foams contains a dispersed soHd phase of organic chemical particles (234—236). The continuous phase is one of the polyols described above for either slab or molded foam as required. The dispersed phase reacts in the polyol using an addition reaction with styrene and acrylonitrile monomers in one type or a coupling reaction with an amine such as hydrazine and isocyanate in another. The soHds content ranges from about 21% with either system to nearly 40% in the styrene—acrylonitrile system. The dispersed soHds confer increased load bearing and in the case of flexible molded foams also act as a ceU opener. 

A composite material (1) is a material consisting of two or more physically and/or chemically distinct, suitably arranged or distributed phases, generally having characteristics different from those of any components in isolation. Usually one component acts as a matrix in which the reinforcing phase is distributed. When the continuous phase or matrix is a metal, the composite is a metal-matrix composite (MMC). The reinforcement can be in the form of particles, whiskers, short fibers, or continuous fibers (see Composite materials). 

Figure 4a represents interfacial polymerisation encapsulation processes in which shell formation occurs at the core material—continuous phase interface due to reactants in each phase diffusing and rapidly reacting there to produce a capsule shell (10,11). The continuous phase normally contains a dispersing agent in order to faciUtate formation of the dispersion. The dispersed core phase encapsulated can be water, or a water-immiscible solvent. The reactant(s) and coreactant(s) in such processes generally are various multihmctional acid chlorides, isocyanates, amines, and alcohols. For water-immiscible core materials, a multihmctional acid chloride, isocyanate or a combination of these reactants, is dissolved in the core and a multihmctional amine(s) or alcohol(s) is dissolved in the aqueous phase used to disperse the core material. For water or water-miscible core materials, the multihmctional amine(s) or alcohol(s) is dissolved in the core and a multihmctional acid chloride(s) or isocyanate(s) is dissolved in the continuous phase. Both cases have been used to produce capsules. 

Figure 4b represents the case where a reactant dissolved in the dispersed phase reacts with the continuous phase to produce a co-reactant. The co-reactant and any remaining unreacted original reactant left in the dispersed phase then proceed to react with each other at the dispersed phase side of the interface and produce a capsule shell. Capsule shell formation occurs entirely because of reaction of reactants present in the droplets of dispersed phase. No reactant is added to the aqueous phase. As in the case of the process described by Figure 4a, a reactive species must be dissolved in the core material in order to produce a capsule shell. 

Figure 4c illustrates interfacial polymerisation encapsulation processes in which the reactant(s) that polymerise to form the capsule shell is transported exclusively from the continuous phase of the system to the dispersed phase—continuous phase interface where polymerisation occurs and a capsule shell is produced. This type of encapsulation process has been carried out at Hquid—Hquid and soHd—Hquid interfaces. An example of the Hquid—Hquid case is the spontaneous polymerisation reaction of cyanoacrylate monomers at the water—solvent interface formed by dispersing water in a continuous solvent phase (14). The poly(alkyl cyanoacrylate) produced by this spontaneous reaction encapsulates the dispersed water droplets. An example of the soHd—Hquid process is where a core material is dispersed in aqueous media that contains a water-immiscible surfactant along with a controUed amount of surfactant. A water-immiscible monomer that polymerises by free-radical polymerisation is added to the system and free-radical polymerisation localised at the core material—aqueous phase interface is initiated thereby generating a capsule sheU (15). 

Drilling fluids are classified as to the nature of the continuous phase gas, water, oil, or synthetic. Within each classification are divisions based on composition or chemistry of the fluid or the dispersed phase. 

Although numerous mud additives aid in obtaining the desired drilling fluid properties, water-based muds have three basic components water, reactive soHds, and inert soHds. The water forming the continuous phase may be fresh water, seawater, or salt water. The reactive soHds are composed of commercial clays, incorporated hydratable clays and shales from drilled formations, and polymeric materials, which may be suspended or dissolved in the water phase. SoHds, such as barite and hematite, are chemically inactive in most mud systems. Oil and synthetic muds contain, in addition, an organic Hquid as the continuous phase plus water as the discontinuous phase. 

Emulsifiers are incorporated in oil and synthetic mud formulations to maintain a stable emulsion of the internal brine phase. These materials include calcium and magnesium soaps of fatty acids and polyamines and amides and their mixtures (123,127). The specific chemistry of these additives depends on the nature of the continuous phase of the mud, ie, whether diesel oil, mineral oil, or a synthetic Hquid. Lime is added along with the fatty acid to form the... 

Dispersions. In phenoHc resin dispersions, the continuous phase is water or a nonpolar hydrocarbon solvent. The resin exists as droplets that have particle sizes of 1—20 p.m and are dispersed in the continuous phase. Aqueous dispersions are prepared either in situ during the preparation of the resin itself or by high shear mixing (25,35). 

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