Stabilization, of emulsions

An important aspect of the stabilization of emulsions by adsorbed films is that of the role played by the film in resisting the coalescence of two droplets of inner phase. Such coalescence involves a local mechanical compression at the point of encounter that would be resisted (much as in the approach of two boundary lubricated surfaces discussed in Section XII-7B) and then, if coalescence is to occur, the discharge from the surface region of some of the surfactant material. 

It was pointed out in Section XIII-4A that if the contact angle between a solid particle and two liquid phases is finite, a stable position for the particle is at the liquid-liquid interface. Coalescence is inhibited because it takes work to displace the particle from the interface. In addition, one can account for the type of emulsion that is formed, 0/W or W/O, simply in terms of the contact angle value. As illustrated in Fig. XIV-7, the bulk of the particle will lie in that liquid that most nearly wets it, and by what seems to be a correct application of the early oriented wedge" principle (see Ref. 48), this liquid should then constitute the outer phase. Furthermore, the action of surfactants should be predictable in terms of their effect on the contact angle. This was, indeed, found to be the case in a study by Schulman and Leja [49] on the stabilization of emulsions by barium sulfate. 

Electrical Stability of Emuisions. The electrical stability test indicates the stability of emulsions of water in oil. The emulsion tester consists of a reliable circuit using a source of variable AC current (or DC current in portable units) connected to strip electrodes. The voltage imposed across the electrodes can be increased until a predetermined amount of current flows through the mud emulsion-breakdown point. Relative stability is indicated as the voltage at the breakdown point. 

Stabilization of emulsions Stabilization of suspensions Stabilization of foams Control of crystal growth... 

The use of stress tests to study the stability of emulsions has been described in Sec. V.C. 

ThF Tadros. Polymeric surfactants , stabilization of emulsions and dispersions. In E Desmond Goddard, JV Gruber, eds. Principles of Polymer Science and Technology in Cosmetics and Personal Care. New York Marcel Dekker, 1999, pp 73-112. 

Lee, G.W.J. and Tadros, Th.F. (1982) Formation and stability of emulsions produced by dilution of emulsifiable concentrates. Part I. An investigation of the dispersion on dilution of emulsifiable concentrates containing cationic and non-ionic surfactants. Colloids Surf,... 

Although most often connected with investigations of solid dosage forms, diffuse reflectance spectroscopy can also be used to characterize alternative formulations. Through the use of a special sample cell, the technique has been used to study the stability of emulsions [37]. In this work, it was found that information could be obtained that pointed toward subtle changes in the emulsion microenvironment. 

V. Bergeron Stability of Emulsion Films. In Proceedings of the Second World Congress of Emulsions 4, 247, Bordeaux, France (1997). 

H. Sonntag, B. Unterberger, and S. Zimontkowski Experimental Investigation of the Steric Stabilization of Emulsions by (Poly)Vinyl Alcohol. Colloid Polym. Sci. 257, 286 (1979). 

A. Meller and J. Stavans Stability of Emulsions with Nonadsorbing Polymers. Langmuir 12, 301 (1996). 

The stability of emulsions is dependent on various parameters such as size of drops and interactions between drops. These are described in the following text. 

During the studies of phase behaviour two types of liquid crystalline phases were identified. LC material was viscous and exhibited intense "white" birefingence. material was apparently homogeneous but of low viscosity and exhibited "multi-coloured" birefringence. The liquid crystalline phases observed in the equilibrium studies of surfactant concentrations up to 25 are unlikely to take part in the self-emulsification process due to the presence of two-phase regions between L2 and liquid crystalline phases however, LC material may account for the improved stability of emulsions formed by 25 surfactant systems (Table II). Figure 4c indicates that by increasing the surfactant concentration to 30 the... 

The foam stability of mixed AEg with a middle chain length distribution is better than the individual lower one. Among all AEg, the mixed Cio,12 9 gives probably the best result on the stability of emulsion to caster oil. Introducing a long hydrocarbon chain in the mixture or a wide distribution in hydrocarbon chain length causes no effect on the emulsion stability (Figure 6). 

Damodaran, S. (2005). Protein stabilization of emulsions and foams. Journal of Food... 

Damianou, K., Kiosseoglou, V. (2006). Stability of emulsions containing a whey protein concentrate obtained from milk serum through carboxymethylcellulose complexation. Food Hydrocolloids, 20, 793-799. 

Jourdain, L., Leser, M.E., Schmitt, C., Michel M., Dickinson, E. (2008). Stability of emulsions containing sodium caseinate and dextran sulfate relationship to complexation in solution. Food Hydrocolloids, 22, 647-659. 

Dalgleish, D. (1997). Adsorption of protein and the stability of emulsions. Trends in Food Science and Technology, 8, 1-6. 

Emulsions and foams are two other areas in which dynamic and equilibrium film properties play a considerable role. Emulsions are colloidal dispersions in which two immiscible liquids constitute the dispersed and continuous phases. Water is almost always one of the liquids, and amphipathic molecules are usually present as emulsifying agents, components that impart some degree of durability to the preparation. Although we have focused attention on the air-water surface in this chapter, amphipathic molecules behave similarly at oil-water interfaces as well. By their adsorption, such molecules lower the interfacial tension and increase the interfacial viscosity. Emulsifying agents may also be ionic compounds, in which case they impart a charge to the surface, which in turn establishes an ion atmosphere of counterions in the adjacent aqueous phase. These concepts affect the formation and stability of emulsions in various ways ... 

Figure D3.4.1 Various extrinsic parameters that can negatively impact the stability of emulsions.

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