Emulsion of water-in-oil

We have an emulsion of oil in water that we need to separate. The oil droplets have a mean diameter of lO " m, and the specific gravity Of the oil is 0.91. Applying a sedimentation centrifuge to effect the separation at a spedd of 5,000 rpm, and assuming that the distance of a droplet to the axis of rotation is 0.1 m, determine the droplet s radial settling velocity. 

The choice of emulsifier has a large part to play in which kind of emulsion you get. Emulsifiers that are soluble in water generally have shorter chains of fats. These make emulsions of oil in water. Emulsi-... 

The emulsifier polysorbate 80 is at the water-soluble end of the spectrum, making good emulsions of oil in water. 

The Sugar Batter Method. This method works by making an emulsion of oil in water with air bubbles in the oil phase. All the other raw materials are dispersed or dissolved in the aqueous phase. 

An example of a food colloid is mayonnaise (a mixture of vegetable oil plus egg yolk and vinegar which is an emulsion of oil in water). 

Colloid stability enters our daily life in many different ways. A visit to the kitchen provides numerous examples of food colloids with microstructure and stability that are, in no small measure, an important aspect of their appeal to the palate For example, mayonnaise —a mixture of vegetable oil, egg yolk, and vinegar or lemon juice —is an emulsion of oil in water and is stable because the lecithin molecules in the egg yolk provide the needed stability. Milk is another example. We have seen others in the vignettes in Chapters 1 and 4. 

Emulsions are mixtures of fluids that are immiscible. Usually one fluid is present as small droplets in another phase. There are emulsions of oil in water, called oil-inwater emulsions (abbreviated as O/W), but also emulsions of water in oil (W/O). The droplet phase is called the dispersed phase, the surrounding phase the continuous phase. Emulsions are important in a great diversity of products. Some examples are ... 

Detergent molecules can stabilize the emulsion of oil in water as well as remove dirt from soiled clothes. A typical detergent is sodium dodecylsulfate (SDS), which has a formula of CH3(CH2)i0CH2SO4 Na+. In aqueous solution, SDS suspends oil or dirt by forming small aggregates of detergent anions called micelles. Propose a structure for micelles. 

In simple colloids, clear distinction can be made between the disperse phase and the disperse medium, e.g., simple emulsions of oil in water (o/w) or water in oil (w/o). 

White powder. Highly ionic and slightly acidic. Reacts with fatty amines to form thick and stable emulsions of oils in water-... 

Distortion of the particles themselves by electrostatic forces. The effect is not seen in latexes, but may be significant in emulsions of oil in water. 

A FIGURE 13.32 Stabilization of an emulsion of oil in water by stearate ions. 

Features Reacts with fat particles to form thick stable emulsions of oils in water Regulatory FDA approved for orals, rectals, topicals NF compliance Manuf/Distrib. Aldrich http //www.sigma-aldrich.com, Sigma Spectrum Quality Prods. http //www.spectrumchemical.com Trade Name Synonyms Acritamer 934 [R.I.T.A. http //www.ritacorp.com], Carbopol 934 [Noveon http //www.noveoninc.com, http //www. carbopol. com, http //WWW. noveoncoatings. com]... 

Features Reacts with fat particles to form thick stable emulsions of oils in water Regulatory FDA approved for topicals NF compliance... 

If in an oil-soap-water system, the proportion of calcium soap to sodium soap is varied, the emulsifying action of the combination of soaps will depend upon the ratio of metal ions. Clowes found out a critical ratio of calcium ion to sodium ion experimentally which produced no emulsion. This critical ratio was Ca Na = 1 4. If calcium is preponderant above this ratio, an emulsion with oil as the continuous phase results, while any preponderance of sodium soap 5delds emulsions of oil-in-water t3Tje. 

The smaller the drop, therefore, the greater its inner pressure. This property can be verified with soap bubbles. By connecting two bubbles (Figure 1.6) of different sizes, one can readily observe that the smaller one empties itself into the larger one. In an emulsion of oil in water, small drops disappear in favor of large ones because of this overpressure, which makes them thermodynamically unstable (a phenomenon known as Ost-wald s ripening). 

In food applications, dextrans Leuconostoc mesenteroides strains product) have been used, usually in combination with other polysaccharides such as gum arabic, for purposes similar to other hydrocolloids. They are highly effective emulsifiers and stabilisers of emulsions of oil in water. They bind water and inhibit the crystallisation of saccharose. Much more extensive use has been found for dextran in pharmacy and medicine (replacement of blood plasma) and in analytical chemistry as a chromatographic material for gel filtration and other applications. 

Stabilizers of this kind allow getting suspension of a non-polar liquid in water (emulsion of oil in water type). If the wetting angle is greater than 90° (5j 3<5j 2) then the powder is adsorbed by the non-polar liquid and one obtains emulsion of water-in oil t3T>e. For the contact value equal to 90 degrees, depending on such factors as number of separate phases, the way how the phase is dispersed, etc., formation of both types of emulsions is possible. 

Bicontinous microemulsions of water in oil type require the use of a larger amount of cosurfactant than macro-emulsion of oil in water t)q)e. These microemulsions are distinct by the stmcture approaching that of liquid crystals, but with a smaller order. 

Separators cannot be expected to handle, waters more highly acid than a pH of 4.5 or more alkaline than a pH of 10 or to handle true emulsions of oil in water such as so-called white water. In such an emulsion the oil is dispersed through a continuous water phase and is carried through the separator. Later the emulsion may be destroyed by dilution or other effects that will liberate the oil. Emulsions of water-in-oil which may contain asphalt, clay, dirt, alkaline earth soaps, lead sulfide, or coke as the emulsifying agent are not usually troublesome. Occasionally, however,... 

There are also fire-resistant h., which are emulsions of oil in water or vice versa. Emulsifiers and additives used may be based on RR. 

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