Preparation of emulsions

Most kinds of emulsions that will be encountered in practice are not formed spontaneously on contact of the phases because they are thermodynamically 

In this case, when the two phases are mixed, the fatty acid salt is formed directly at the oil-water interface. 

There are other variations of this approach that involve the phase inversion temperature (PIT) (see Section 3.6.1). In one method, an emulsion is formed at a temperature of few degrees lower than the PIT where the interfacial tension is quite low and small droplets can be formed. The emulsion can then be quickly cooled. Another method uses a controlled temperature change to cause an emulsion to suddenly change from a coarse O/W emulsion, through a microemulsion phase, into a fine W/O emulsion [17]. 

The traditional methods of emulsion preparation, especially those involving stirring and shaking, tend to lead to uncontrolled and wide drop size distributions. Several methods for the preparation of fairly monodisperse emulsions exist, of which the simplest is probably the extrusion of a dispersed phase through a pipette 

There are some rules of thumb for predicting the type of emulsion that will form under certain circumstances. It is emphasized at the outset that there are exceptions to each of these rules, and sometimes one will work where the others do not. They are presented here because they remain useful for making initial predictions. 

Some of the above emulsion preparation methods are also used as tests of the effectiveness of different surfactants in stabilizing emulsions. For example, the 

The HLB concept, introduced in Section 3.6.1 is probably the most useful approach to predicting the type of emulsion that will be stabilized by a given surfactant or surfactant formulation. The HLB concept was introduced [207,209] as an empirical scale that could be used to describe the balance of the size and strength of the hydrophilic and lipophilic groups on an emusifier molecule. Originally used to classify Imperial Chemical Industries non-ionic surfactant series of Spans and Tweens the HLB system has now been applied to many other surfactants, including ionics and amphoterics. 

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Preparation of Emulsions. An emulsion is a system ia which one Hquid is coUoidaHy dispersed ia another (see Emulsions). The general method for preparing an oil-ia-water emulsion is to combine the oil with a compatible fatty acid, such as an oleic, stearic, or rosia acid, and separately mix a proportionate quantity of an alkah, such as potassium hydroxide, with the water. The alkah solution should then be rapidly stirred to develop as much shear as possible while the oil phase is added. Use of a homogenizer to force the resulting emulsion through a fine orifice under pressure further reduces its oil particle size. Liquid oleic acid is a convenient fatty acid to use ia emulsions, as it is readily miscible with most oils. 

Preparation of Emulsions. The entire aqueous phase was stirred until all solids were dissolved. Sufficient water was withheld from the formulation so small volumes of experimental and control components could be added to emulsion subsamples. Sulfuric acid (1 N) was added to the aqueous phase to decrease the pH to 5.7. The two phases in separate containers were blanketed with nitrogen, sealed, and heated to 75 in an 80 water bath (about 30 minutes). The hot oil phase was stirred slowly and blanketed with nitrogen, then the hot aqueous phase was quickly added while stirring. The emulsion was blanketed with nitrogen and slowly stirred (about 2 hours) in the stoppered container until ambient temperature ( 25 ) was reached. Subsamples of the master batch were removed for the addition of experimental components and stored in 1-oz containers. The containers had been washed with hot tap water, deionized water, and methanol, then dried at 120 . 

The preparation of formulations may involve the principles of physics and mechanics. The preparation of emulsions, fine particle materials, etc., constitutes an important part of insecticide development. A knowledge of the kinds of equipment used in the preparation of formulations enables the chemist to handle the job with greater facility. 

Distinctly different approaches to avoid these problems and still achieve high viscosities were conceived and applied. The different approaches can be categorized as 1) preparation of emulsions or foams and 2) addition of crosslinkers to the polymer. Two separate processes which utilized crosslinking of polymer gelling agents were pursued. These are the use of secondary (or delayed) gelling agents and the use of metallic crosslinkers added on-site. 

There are a large number of industrial processes which employ cavitation as an energy source for the generation of fine emulsions and dispersions. One of the earliest devices which was developed for this purpose was the so-called liquid whistle (see Chapter 7) and this continues to be used widely. Typical examples of the uses of such whistles include the preparation of emulsion bases for soups, sauces or gravies which consist of a premix of water, milk powder, edible oil and fat together with flour or starch... 

Preparation of Emulsions. Monomer, water, and emulsifier were mixed in an apparatus similar to that described by Bartholome et al. (4, 6). However, instead of the Ultra-Turrax, a vibrating plate stirrer was used. 

Fig. 1. Preparation of emulsion for immunization. Two iuer Jock glass syringes connected by a three-way plastic stopcock are used to form a stable emulsion of antigen and adjuvant.

Membrane-wetting properties may be carefully considered in the membrane selection. In general, the membrane surface where the droplet is formed should not be wetted by the disperse phase. Therefore, a w/o emulsion is prepared using a hydrophobic membrane and an o/w emulsion is prepared using a hydrophilic membrane. On the other hand, w/o and o/w emulsions were successfully prepared using pretreated hydrophilic and hydrophobic membranes, respectively. The pretreatment basically consisted in absorbing the continuous phase on the membrane surface so that to render the membrane nonwetted by the disperse phase [14, 23, 25]. The presence of emulsifier in the disperse phase represents another strategy that permits the preparation of emulsions with a membrane wetted by the disperse phase. 

However, some of these microreaction components may be successfully applied for specific purposes, e.g. for the production of colloidal particles whose precipitation process is sensitive to mixing or for the preparation of emulsions for cosmetic industry. 

Uses Preparation of emulsions, sizing paper, adhesives, light filters. 

Preparation of Emulsions Emulsions can be prepared by shaking or stirring the two phases with the addition of a suitable emulsifier. The type of emulsion formed, depends on the angles of contact of the two liquids with the solid emulsifier. 

N. Yan and J. H. Masliyah, Characterization and demulsification of solids-stabilized oil-in-water emulsions. Part 1. Partitioning of clay particles and preparation of emulsions, Colloids Surf. A 96, 229-242 (1995). 

On a manufacturing scale rotor stator mills have proven to be very efficient. Their use in the preparation of emulsions has been described in a wide body of literature [7]. When preparing suspoemulsions the same principles can be applied. 

The influence of the vessel size in the preparation of emulsions under ultrasonic energy in discrete systems has been established in terms of parameter R, which is the ratio of the height of the liquid-liquid mixture in the vessel to the diameter of the vessel. Two cylindrical vessels of different size (specifically with an R value of 1 and 2.5) were used under the same working conditions. Similar to the tip diameter, the differences in emulsification efficiency between the two vessels were small at a high (93 W) or very low (15 W) ultrasonic power. On the other hand, at 33 and 63 W, the efficiency was higher for the vessel with R= 1 viz. a cylindrical vessel) [56],... 

A study on the influence of the viscosity of the dispersed phase in the preparation of emulsions of vegetable oils (olive, soyabean and linseed) in water with US assistance revealed that replacing the oil with the highest viscosity and interfacial tension — olive oil — with soyabean oil, which has slightly lower viscosity and interfacial tension, caused virtually no reduction in droplet size. Linseed oil, with much lower viscosity and interfacial tension than olive oil, exhibited a much smaller Sauter diameter than the latter viz. 0.47 (xm versus 0.62 pm). Breaking low-viscosity droplets requires less vigorous cavitation shock waves than breaking more viscous ones [49]. 

The pharmaceutical field is among those most widely exploiting ultrasonic emulsification (mainly for the preparation of emulsion-based drugs). Thus, US emulsification has been recently used to prepare biodegradable nanoparticles that can in turn be used to obtain drug-loaded biodegradable microspheres. The method involves ultrasonic emulsification in a continuous flow system to obtain suspended nanoparticles, followed by collection of the particles, solvent extraction and evaporation [49]. 

Preparation of Emulsions. The mixture oil-lipopeptide is heated to 70 C under agitation for complete homogeneization. It is then cooled to 45°C and water is added. The agitation is maintained throughout the preparation and until the system is cooled to room temperature (9). 

A section of the present chapter is devoted to a rather detailed description of the basic thermodynamic and kinetic principles involved in the various swelling procedures. This seems justified in view of the present, and potential, applicatioxis of these principles to the preparation of emulsions and polymer dispersions. The swelling procedures developed so far have led to the first successful methods for preparation of large, monodisperse particles. 

Another, more specific method for the preparation of emulsions of Z, involves the addition of Z to a preformed mixture of an ionic emulsifier, a long-chain fatty alcohol, and water. In this way, the rapid formation of a stable emulsion may he obtained at ordinary stirring with relatively modest amounts of emulsifier. The mechanism of Ais process is still not satisfactorily explained. Also, subsequent polymerization (in the case where Zi is a monomer) may lead to polymerization with initiation in monomer droplets. 

Membrane reactors using biological catalysts can be used in enantioselective processes. Methodologies for the preparation of emulsions (sub-micron) of oil in water have been developed and such emulsions have been used for kinetic resolutions in heterogeneous reactions catalyzed by enantioselective enzyme (Figure 43.4). A catalytic reactor containing membrane immobilized lipase has been realized. In this reactor, the substrate has been fed as emulsion [18]. The distribution of the water organic interface at the level of the immobUized enzyme has remarkably improved the property of transport, kinetic, and selectivity of the immobilized biocatalyst. 

Membrane emulsihcation has been recently proposed for the preparation of stable and uniform-sized microcapsules [27]. Membrane emulsihcation is a technology that allows to obtain uniform emulsions at low energy input compared to the emulsion prepared using high-pressure homogenizers and rotor/stator systems therefore, it is very useful for the preparation of emulsions containing labile compounds such as bioactive molecules sensihve to shear stress [28]. 

The phenomenon of droplet breakup is of great importance in the preparation of emulsions. If a stream of liquid is injected with little turbulence into another liquid with which it is immiscible, the cylinder that may form is unstable, breaks down in several spots, and breaks up into droplets (Figure 2a). If the injection rate is such as to produce turbulence, the disruption is faster, and many smaller droplets are produced (Figure 2b). If in addition the liquid impinges against a surface, many smaller droplets will be formed. 

Preparation of Emulsions. For this purpose we used the assembly described by Bartholom6 et al. (6) all parts of the apparatus could be flushed with argon. Water, monomers, and emulsifier were vigorously agitated for 15 minutes. Ac-... 

Many salts reduce the viscosity of aqueous acacia solutions, while trivalent salts may initiate coagulation. Aqueous solutions carry a negative charge and will form coacervates with gelatin and other substances. In the preparation of emulsions, solutions of acacia are incompatible with soaps. 

Diethanolamine is primarily used in pharmaceutical formulations as a buffering agent, such as in the preparation of emulsions with fatty acids. In cosmetics and pharmaceuticals it is used as a pH adjuster and dispersant. 

Monoethanolamine is used primarily in pharmaceutical formulations for buffering purposes and in the preparation of emulsions. Other uses include as a solvent for fats and oils and as a stabilizing agent in an injectable dextrose solution of phenytoin sodium. 

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