Emulsion stability factors

Figure 13. Electrophoretic mobility (Fen Kem 3000) of the emulsion from Figure 12 after cationic polymer addition (A). The cationic polymer has neutralized the oil droplet surface charge and electrostatically destabilized the emulsion. The photomicrograph (B) shows this destabilized emulsion that has begun to flocculate or a lomerate but that is not coalescing. This electrostatic destabilization is not the only factor affecting emulsion stability. Factors such as interfacial tension and film strength can prevent coalescence of the emulsion droplets, even though they can now closely approach each other and ag omer-...

Eccleston [19] reviewed the emulsion stability factors on the basis of the HLB and of the DLVO theory. He emphasized the Friberg school results which show that the presence of liquid crystals stabilizes the emulsions by delaying the film-thinning process and, consequently, by reducing the rate of coalescence. He also mentioned stabilization by the formation of a gel network (surfactant-fatty alcohol-water system). Dahms [20] explained the role of fatty alcohol as a viscosity modifier on the basis of lamella-phase generation. 

C. Long-Range Forces as a Factor in Emulsion Stability... 

In view of the importance of macroscopic structure, further studies of liquid crystal formation seem desirable. Certainly, the rates of liquid crystal nucleation and growth are of interest in some applications—in emulsions and foams, for example, where formation of liquid crystal by nonequilibrium processes is an important stabilizing factor—and in detergency, where liquid crystal formation is one means of dirt removal. As noted previously and as indicated by the work of Tiddy and Wheeler (45), for example, rates of formation and dissolution of liquid crystals can be very slow, with weeks or months required to achieve equilibrium. Work which would clarify when and why phase transformation is fast or slow would be of value. Another topic of possible interest is whether the presence of an interface which orients amphiphilic molecules can affect the rate of liquid crystal formation at, for example, the surfaces of drops in an emulsion. 

The following factors (which depend on the nature of the emulsifying agent and/or on a suitable choice of formulation and manufacturing conditions) favour emulsion stability ... 

The effects of the concentration of the dispersed phase, emulsifier type and concentration on the inversion of water-in-oil emulsions have been described above. However, since in this chapter, it is proposed to examine the effects of a multi-ingredient system on emulsion stability, each of the following factors must be considered emulsion formation, stability, instability, effects of shear and effects of ingredients (Becher, 1977). 

Boyd, J., Parkinson, C., Sherman, P. 1972. Factors affecting emulsion stability and the HLB concept. J. Coll. Inter/. Sci. 41, 359-370. 

Very often, the microstructure and the macroscopic states of dispersions are determined by kinetic and thermodynamic considerations. While thermodynamics dictates what the equilibrium state will be, kinetics determine how fast that equilibrium state will be determined. While in thermodynamics the initial and final states must be determined, in kinetics the path and any energy barriers are important. The electrostatic and the electrical double-layer (the two charged portions of an inter cial region) play important roles in food emulsion stability. The Derjaguin-Landau-Verwey-Oveibeek (DLVO) theory of colloidal stability has been used to examine the factors affecting colloidal stability. 

Milk replacer fat emulsion. One important application of lecithin in animal feeds is as an emulsifier (314). As an example, milk replacer fat is emulsified to improve product wetting and dispersion upon mixing, to help minimize fat separation (i.e., emulsion stability), and to significantly reduce fat particle size, allowing improved fat digestibility. As an emulsifier in milk replacers, lecithin is used at 3-12% of the added fat. The type of lecithin used is affected by factors such as fat type, protein type, and the presence of stabilizers. 

Foam stability is governed by similar factors as emulsion stability. Thus in a soap foam the negative charges located at the air-water interface lead to repulsion as the... 

Considering stability to both aggregation and coalescence, the factors favoring emulsion stability can be summarized as follows ... 

Electrokinetics. Bottle tests and centrifugation may be somewhat crude, but they do offer a relative measure of emulsion stability that combines, to some extent, all of the factors that affect stability. Electrokinetic measurements are somewhat more elegant because they allow direct measurement of the degree of electrostatic stability in an emulsion system. The zeta potential, or relative magnitude of the electric charge on the surface, is... 

Film stability and interfacial forces are important in determining emulsion stability and the likelihood of creaming or complete separation of the phases. Characterization of these interfacial effects is an important factor in determining the fundamental properties that might ultimately determine coalescence kinetics. Some relevant papers and reviews have been published elsewhere (54, 89-96). 

This evaluation illustrates that emulsion water concentration should generally be reduced until the viscosity begins to be significantly increased. In selecting the actual optimum concentration for a specific case, other factors such as the effect of water concentration on emulsion stability, the effect of total fiow rate on pump efficiency, and the cost and availability of water should also be considered. 

Several factors affect demulsifier performance temperature, pH, and the nature of the aqueous-phase salt. In most cases, an increase in temperature results in a decrease in emulsion stability. Consequently, for a particular emulsion, less demulsifier is required at higher treating temperatures to effect the same degree of treatment. Studies (i) on the effect of pH on the instability of crude-oil-water emulsions have shown that a pH of 10.5 produced the least stable emulsions. Furthermore, basic pH produced oil-inwater emulsions and acidic pH generated water-in-oil emulsions. 

The chapter should allow an appreciation of the factors leading to emulsion stability and physical instability, including flocculation and coalescence. Approaches to the formulation of emulsions to provide vehicles for drug delivery and parenteral nutrition (the main uses in pharmacy) should be understood. 

Most of the drugs have got the property to promote relatively stable oil in water emulsions. A study of a sulphonamide drug sulpha-pyridine reveals that it yields a stable emulsion. The emulsion behaviours have been interpreted by studying flocculation, coalescence, electro-kinetic potential, potential energies and stability factors. These studies were made as a function of nucleic acids, DNA and RNA (Deoxy-ribonucleic acid and Ribonucleic acid) which were chosen in accordance with their biological significance. 

The stability factor, W, is determined to give clear insight into the emulsion stability with the help of the equation used elsewhere (17) ... 

The above discussion of emulsion stability is further supported by the stability factors calculated with the help of equations 11, 12, and 14. The results are given in Table VI. All values are greater than 10 KT, the condition derived by Derjaguin for stable dispersions. These values are higher than the corresponding values of V/KT, because in this estimation, the effect of van der Waal s interaction is not taken into account. 

Table VI. on Addition Stability Factors of RNA and DNA. of Sulfapyridine-Stabilized Emulsion ...

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