Destabilization of emulsions

Emulsions are thermodynamically unstable. We cannot completely stop or avoid this process as the droplets collide what is of course important is that the droplets do not adhere (stick) when they 

Creaming or sedimentation can be caused by density differences, as explained by Stokes law (see later and Chapter 8). Sometimes, many of the above phenomena are termed generally as aggregation. In the case of coalescence, the droplets must encounter each other, they then lose their original shape coalescence is an irreversible phenomenon that eventually may lead to complete phase separation (breaking). On the other hand, flocculation and creaming are reversible. The number of individual droplets can acmally 

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Occasionally perfumes may cause destabilization of emulsions. This is an indication of inherent borderline stability of the emulsion system and should be remedied, wherever possible, by a change in the product formulation. Where this is out of the question, the only remedy is a laborious trial-and-error reformulation or replacement of the perfume compound. If high levels of phenylethyl alcohol or benzyl alcohol occur in the perfume, they may be the cause of the problem. 

Fat crystallization has been extensively studied in bulk fats and, to a lesser extent, in emulsified fats. It has been shown that the crystallization behavior of a fat will proceed quite differently, depending on whether it is in bulk or emulsified form (4,5). Authors have examined the effect of the state of dispersion on the crystallization mechanisms (nucleation, crystallization rate) and polymorphic behavior (6-11) of partial- and triglycerides in bulk and emulsified form. Understanding the mechanisms of emulsion nucleation and crystallization is one of the first steps in understanding the destabilization of emulsions and partial coalescence, e.g., stabilization of liquid fat emulsions by solid particles (fat) or control of the polymorphic form of crystals during the process of partial coalescence to control the size of aggregates and textural properties. 

The influence of a shear field on emulsion crystallization is of great interest as it relates to behavior during product processing and distribution. Emulsions can be destabilized under shear in a controlled manner to deliver desirable properties uncontrolled or unintentional destabilization may lead to poor product performance. Comparisons of emulsions under perikinetic (at rest) and orthokinetic (under shear) conditions were made in an effort to understand the role of shear on the stability of the systems studied. Davies et al. (22) found stability of triglyceride emulsions containing crystals to be sensitive to both shear and crystal concentration. Crystal morphology also plays an important role in the destabilization of emulsions under shear. Boode and Walstra (4) reported the presence of needle-like... 

Fig. 8. The effect of adsorbed protein type and concentration on the destabilization of emulsions during whipping. , whey protein isolate emulsions , sodium caseinate emulsions (33).

Stabilization and partial destabilization of emulsions and foams by controlling the state of dispersion and agglomeration of oil droplets or fat globules... 

Biosurfactant activities can be determined by measuring the changes in surface and interfacial tensions, stabilization or destabilization of emulsions, and hydrophilic-lipophilic balance. Surface tension at the air/water and oil/water interfaces can easily be measured with a tensiometer. The surface tension of distilled water is 72 mN/m, and the addition of surfactants lowers this value to about 30 mN/m [5]. 

Much of what has been written above for foams is, in principle, applicable to emulsions, in the latter systems the nonpolar disperse phase being a second liquid (oil) rather than a gas (air). However, published work on the stabilization/destabilization of emulsions using combinations of polymer and surfactant has been limited. Therefore, it is appropriate again to consider hypothetical simplistic models to depict possible interfacial structures. Normally, as in foaming, one would anticipate that the faster-diffusing surfactant, by lowering the interfacial tension, would facilitate dispersion of the oil droplets in water (or vice versa) and the polymer reinforce the interfacial structure (Fig. 13). 

The ABS polymer is recovered through coagulation of the ABS latex. Coagulation is usually achieved by the addition of an agent to the latex which destabilizes the emulsion. The resulting slurry can then be filtered or centrifuged to recover the ABS resin. The wet resin is dried to a low moisture content. A variety of dryers can be used for ABS, including tray, fluid bed, and rotary kiln type dryers. 

The traditional view of emulsion stability (1,2) was concerned with systems of two isotropic, Newtonian Hquids of which one is dispersed in the other in the form of spherical droplets. The stabilization of such a system was achieved by adsorbed amphiphiles, which modify interfacial properties and to some extent the colloidal forces across a thin Hquid film, after the hydrodynamic conditions of the latter had been taken into consideration. However, a large number of emulsions, in fact, contain more than two phases. The importance of the third phase was recognized early (3) and the lUPAC definition of an emulsion included a third phase (4). With this relation in mind, this article deals with two-phase emulsions as an introduction. These systems are useful in discussing the details of formation and destabilization, because of their relative simplicity. The subsequent treatment focuses on three-phase emulsions, outlining three special cases. The presence of the third phase is shown in order to monitor the properties of the emulsion in a significant manner. 

Before determining the degree of stabiUty of an emulsion and the reason for this stabiUty, the mechanisms of its destabilization should be considered. When an emulsion starts to separate, an oil layer appears on top, and an aqueous layer appears on the bottom. This separation is the final state of the destabilization of the emulsion the initial two processes are called flocculation and coalescence (Fig. 5). In flocculation, two droplets become attached to each other but are stiU separated by a thin film of the Hquid. When more droplets are added, an aggregate is formed, ia which the iadividual droplets cluster but retain the thin Hquid films between them, as ia Figure 5a. The emulsifier molecules remain at the surface of the iadividual droplets duiing this process, as iadicated ia Figure 6. 

As a related matter it is easily understood that addition of salts at a certain concentration destabilizes an emulsion. It may be concluded that if an emulsion remains stable at electrolyte contents higher than those cited in the preceding paragraphs, the stabiUty is not the result of electric double-layer repulsion, which may be useful information to find the optimum manner for destabilization. 

In the simplest emulsions just described, the final separation is into two Hquid phases upon destabilization. The majority of emulsions are of this kind, but in some cases the emulsion is divided into more than two phases. One obvious reason for such a behavior is the presence of a material that does not dissolve in the oil or the water. One such case is the presence of soHd particles, which is common in emulsions for food, pharmaceuticals, and cosmetics. Another less trivial reason is that the surfactant associates with the water and/or the oil to form a colloidal stmcture that spontaneously separates from the two hquid phases. This colloidal stmcture may be an isotropic Hquid or may be a semisoHd phase, a Hquid crystal, with long-range order. 

Coalescence Fusion of smaller lipid emulsion particles forming larger particles, resulting in destabilization of the emulsion. 

Dickinson, E., Owusu, R.K., Williams, A. (1993b). Orthokinetic destabilization of a protein-stabilized emulsion by a water soluble surfactant. Journal of the Chemical Society, Faraday Transactions, 89, 865-866. 

Chemical addition. Since the chemical must contact each stabilized water droplet in order to destabilize it, Che chemical should be applied so that it is thoroughly mixed with all of the emulsion. This can be accomplisned by batch treating, that is. mixing the demulsifier with a quantity of emulsion after it has been produced or by continuously injecting the dcmulsilier into the emulsion as it is being produced Mosi ofien continuous injection is used... 

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