Simple Emulsions Preparation

Emulsion Preparation. Preparing a transport emulsion is a fundamentally simple operation that includes the steps of forming a water-brine solution of the emulsion-stabilizing composition followed by a shearing process in which the crude oil and aqueous phases are metered to a specific mixing device. 

It has been demonstrated that liposomes, micelles, certain oil emulsions, and macromolecules (e.g., serum albumin) will keep the sensitizer molecules in a monomeric form (Jori, 1992 Hoebeke, 1995). The fact that most sensitizers are heavily charged and in many cases present as zwitterions, combined with their extensive polycyclic nature, makes some of these compounds particularly difficult to incorporate in a simple emulsion or liposome preparation. The zwitterions, in particular, can be almost insoluble in hydrophilic and lipophilic media. Alternative formulation approaches may therefore be required for this group of sensitizers. 

A preliminary investigation was made of the toxicity of the graft copolymer emulsion using human erythrocytes as a model cell line. First of all the toxicity of an emulsion prepared from 5% HEMA and 1% alginate in phosphate buffered saline was estimated by examination of a mixture with 10% hematocrit after 1 h storage. No lysis could be observed and the cells could be separated and disrupted in distilled water. We then encapsulated 10% hematocrit in the same emulsion and stored the capsules in isotonic saline for one week. The cells were recovered by disruption of the capsules with citrate and were perceived as healthy as per the simple tests outlined above. 

A simple emulsion can be prepared by shaking a solution of household liquid detergent (washing-up liquid) diluted 1 10 with an equal volume of white spirit (turpentine substitute) or a few drops of cooking oil. The resulting emulsion is stable for several hours. 

The emulsions so far described have been mainly of the simple 0/W type. However, because of their utility in other fields (e.g., cosmetology), an interest is developing in food applications of multiple emulsions, i.e., water-in-oil-in-water emulsions, since fliey modify the behavior of the fat and also offer the potential to carry, in their interior water droplets, materials of nutritional interest (172, 173). However, flic formulation and con trol of such preparations is much more difficult than for simple emulsions (174). The basic principles of such emulsion formulation are well known the water droplets within the oil droplet need to be stabilized using a mixture of lipophilic emulsifiers, whereas the stabilization of the oil droplets requires rather a hydrophilic surfactant. Evidently, the preparation of such emulsions cannot be preformed in a single stage, but requires the preparation of a W/O emulsion first, and then dispersion of this emulsion into an aqueous medium. 

Double emulsions may offer some advantages for food appheations mainly with relation to their eapability to encapsulate (or entrap) in the internal eompartments some water-soluble substances that are flien slowly released. The double emulsion can also be used in the food industry where an external water phase is more aeeeptable in terms of palatability than an oil one (93,94). On this basis several new products have been patented in the form of W/O/W emulsions, as salted creams (encapsulation of salt), aromatic mayonnaise, etc. (95-98). Fiuther food applications are related to the double-emulsion dielectric properties for example one can prepare a W/O/W system having the same volume fraction of the dispersed phase and the same texture as a simple emulsion, but with a lower oil eontent (due to the existence of the aqueous eompartments in the food globules), i.e., low-calorie mayonnaise (93). 

Professors Nissim Garti and Axel Benichou review formation and preparation of intricate multiple emulsions, of both the water-in-oil-in-water and oil-in-water-in-oil types. Emulsions of this type occur especially when mixtures of both hydrophobic and hydrophilic stabilizers are used. These mixtures can be either commercial or naturally occurring. This chapter is an important complement to the traditional view of simple emulsions with only one dispersed phase. 

Emulsification by comminution (20-22) is very com-mon, the most widely used procedure for emulsion preparation. It can be earned out with very simple equipment, as for instance, a spoon in a bowl during the preparation of salad dressing in the kitchen for mixing water and oil. 

Because they involve various phases and interfaces, multiple emulsions must be inherently unstable, even more so than conventional simple emulsions. Their surfactant requirements are such that two stabilizing systems must be employed one for each oil-water interface. Each surfactant or mixture must be optimized for the type of emulsion being prepared but must not interfere with the companion system designed for the opposite interface. Longterm stability, therefore, requires careful consideration of the characteristics of the various phases and surfactant solubilities. 

As noted above, because of the possible instabihty of the primary emulsion, great care must be taken in the choice of the secondary dispersion method. Excessive mechanical agitation such as in colloid mills, high-speed mixers, and sonication could result in coalescence of the primary emulsion and the production of a simple emulsion. The evaluation of the yield of filled secondary emulsion drops, therefore, is very important in assessing the value of different preparation methods and surfactant combinations. 

Another interesting phenomenon that can be studied by calorimetry is so-called composition ripening. In that case, an 0/W emulsion can be formed in which the dispersed medium is characterized by droplets of two different oils in a common aqueous solvent. The mixed solution is prepared by blending two different 0/W simple emulsions of well-known compositions. An instability is then created in the emulsion, due to the difference in the nature of the drops. The oils will tend to diffuse through the water medium from one drop to another, finally forming mixed droplets of the same composition. 

As with macroemulsions (see Chapter 6), several procedures may be applied for emulsion preparation simple pipe flow (low agitation energy L), static mixers and general stirrers (low to medium energy, L-M), high speed mixers such as the Ultra-... 

Emulsions. Emulsion fluids and foams came into routine use in competition with crosslinked fluids during 1970-80. Simple, barely stable emulsions had been used early in fracturing. These were mainly emulsified acids that "broke" when the acid spent on the formation surfaces. In the late 1960 s Kiel became a proponent of very high viscosity oil fluids as a method to place exceptional (at the time) amounts of proppant(337,338). To avoid the frictional resistance typical of gelled oils he advanced the concept of preparing a very viscous oil-external emulsion with one part fresh water, 0.1% sodium tallate surfactant, and two parts oil. The viscous emulsion had to be pumped simultaneously with a water stream to minimize frictional pressure. This process was clumsy and still... 

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