Emulsion generally

Dispersed systems, such as emulsions, have also been employed to achieve high drug loading for parenteral administration. Emulsions generally consist of a vegetable oil (e.g., soybean), a phospholipid surfactant (e.g., lecithin), and glycerol added for isotonicity. The surfactant (emulsifier) is necessary to provide a barrier to agglomeration of the emulsion droplets. Unlike micellar solutions that are thermodynamically stable,... 

Water-in-oil emulsions, generally appear to be black, do not dilute with water, and have electrical conductivity lower than that of the brine. The viscosities may be very high, and the shear behavior is thixotropic. 

Scale of Operation The size of the batch being crystallized may influence rate of crystallization. For example, crystallization from an emulsion generally occurs at a lower temperature than for the bulk fat based on the separation of catalyzing nucleation sites. In an emulsion, the catalyzing nucleation sites are more dispersed (spread through the number of droplets) and this leads to nucleation at a lower temperature than the same fat in bulk phase. 

The solids cannot be treated as oil droplets even if the size and size distribution of the solids are similar to the oil droplets. The addition of solids to an emulsion generally gives a higher viscosity than the pure emulsion at the same total concentration. 

The viscosity of an oil-in-water emulsion generally varies in proportion to the continuous-phase viscosity. If concentrated brines or brines containing additives are to be used, then the continuous-phase viscosity may be substantially greater than that of water, and a correction should be applied. Speciflc adjustment factors for this effect may be estimated as the ratio of viscosities of the brines in the known and unknown emulsions. 

Industrial liquid-liquid extraction most often involves processing two immiscible or partially miscible liquids in the form of a dispersion of droplets of one liquid (the dispersed phase) suspended in the other liquid (the continuous phase). The dispersion will exhibit a distribution of drop diameters d, often characterized by the volume to surface area average diameter or Sauter mean drop diameter. The term emulsion generally refers to a liquid-liquid dispersion with a dispersed-phase mean drop diameter on the order of 1 pm or less. 

Figure 11 shows all of the fresh emulsion data obtained in this study compared with Sherman s model. Values of a for these emulsions ranged from 0.60 to 0.62. The 1.0% NaCl emulsions generally had the highest relative viscosities and the highest [Pg.484]

Semi- or meso-stable emulsions represent the third way water can be present in oil. These are formed when the small droplets of water are stabilized to a certain extent by a combination of the viscosity of the oil and the interfacial action of asphaltenes and resins. For this to happen, the asphaltene or resin content of the oil must be at least 3% by weight. The viscosity of meso-stable emulsions is 20 to 80 times higher than that of the starting oil. These emulsions generally break down into oil and water or sometimes into water, oil, and stable emulsion within a few days. Semi- or meso-stable emulsions are viscous liquids that are reddish-brown or black in colour. 

The term microemulsion was initially introduced in 1959 by Schulman who suggested the following definition A microemulsion is formed on addition of an aliphatic alcohol (co-surfactant) to an ordinary emulsion. Generally, micro-emulsions are defined as thermodynamically stable homogeneous mixtures of oil and water stabilised by surfactants and, in some cases, by co-surfactants. Thus, a water in oil microemulsion, i.e. a reversed micellar solution, is a transparent, isotropic and thermodynamically stable fluid in which nanometer-sized water droplets are dispersed in a continuous oil phase. 

One of the important features of solvent removal methods of encapsulation is the rate at which the organic solvent is removed from the microdroplets of the emulsion. Generally the solvent can be removed either by evaporation or extraction, or by combined procedures. 

Even though emulsions generally need to be as stable as possible, there are several food produets where the opposite effeet is desired, so a shelf-stable emulsion ean be eontrol-lably destabilized when required. Sueh emulsions are the basis for produets such as whipped toppings and ice cream and generally depend for their effect on the processes of partial coalescence (168-170) and destabilization by whipping air bubbles into the mixture, at which time the interfacial layer of the emulsions may be mechanically broken and liquid oil spread aroimd the air-solution interface. 

This was a hard-earned lesson for developers of the semi-aqueous process. Unless soil materials are familiar in nature and quantity, laboratory tests are essential to commerdal success with the semFaqiteous process An emulsion is a mixture of two (or more) immiscible fluids. Emulsions are unstable, do not form spontaneously, and their formation is aided by addition of mechanical energy to the fluid mixture. Over a time span of minutes to hours, emulsions generally tend to revert to the stable state of the phases comprising them. 

Currently approved parenteral lipid emulsions generally contain safflower or soybean oils, which are both rich in omega-6 polyunsaturated fatty acids, which may contribute to liver damage [69 ]. Fish oil-based lipid emulsions, which are primarily composed of omega-3 polyunsaturated fatty acids, have been used to reduce hepa-totoxicity (see also biliary tract below). 

Emulsions appear to have even a greater margin of safety than water gels and slurry explosives in impact sensitivity tests. When subjected to burning tests, emulsions generally do not detonate. As in the case of all explosives, however, results obtained from tests performed under controlled conditions do not guarantee that a given product will behave in a like manner in the field. Emulsion explosives must be handled and used with the same attention to safety afforded any explosive material. 

Details of the synthesis and larger-scale production of a number of molecular explosives including dynamites are given in the four-volume series by Urbanski Chemistry and Technology of Explosives Pergamon Press, 1964-84) and in various military books such as reference 8. Formulations of commercial slurries and emulsions generally are considered proprietary and are described mainly in the patent literature. Some specific... 

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