Aspects of emulsion stability

Emulsions have been defined [5] as heterogeneous systems of one liquid dispersed in another in the form of droplets usually exceedingO.l xm in diameter. The two liquids are immiscible, chemically unreactive, and form systems characterized by a minimal thermodynamic stability. 

Low inrerfocicl tension allows drop detormohon in reosing dmojnt of liquid between collision surfaces 

Emulsion instability is manifested in changes in the physical properties of the dispersion such as its droplet size distribution, its rheological properties or other parameters which are a consequence of the coalescence of globules or their flocculation, that is, of the alteration in the real or effective mean globule diameter, respectively. Flocculation, which is often the precursor of coalescence can affect the appearance of both liquid and solid emulsions. It accelerates the rate of creaming or settling which in itself is regarded as a form of instability. 

Inversion of emulsion type is rare in practice although localized inversion may occur through interaction of the Components of the systems with packaging materials. This type of instability is dealt with later in relation to phase volume and emulsifier type. 

The problem is to prevent instability, not only to maintain the appearance of the emulsion, but so that the characteristics of the emulsion and of medicaments dissolved in the emulsion are as little changed on ageing as possible. As an example, ageing might alter the absorption of heparin from O/W emulsions where absorption of heparin appears to be directly related to the particle size and total surface area of the oil droplets [11]. Fat emulsions are used extensively in intravenous feeding [12] where it is vital that particles remain below 1 in diameter to avoid thrombophlebitis and other complications, but the state of the art is exemplified by the statement [13], that the emulsions must be stored in a refrigerator and no antibiotics, vitamins or potassium supplements added because they may break the emulsions . Lynn [14] reports some experiments on the addition of disodium carbenicillin and sodium cloxacillin to intravenous lipid emulsions which verify this statement. The special case of intravenous emulsions is dealt with in Section 8.7.2. 

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Detailed description of theory, measurements, and applications in emulsion science covering all aspects of emulsion stability. 

Isaacs, E.E. Chow, R.S. Practical Aspects of Emulsion Stability in Emulsions, Fundamentals and Applications in the Petroleum Industry, Schramm, L.L. (Ed.), American Chemical Society Washington, 1992, pp. 51-77. 

Isaacs and Chow Practical Aspects of Emulsion Stability... 

Stability is important for cosmetic skin care products from the points of view of function and also shelf-life. Stability against aggregation is important but fairly easily dealt with because most of these products are formulated to have a yield stress [33]. Stability against coalescence is very important but less straightforward (see Chapter 5 for the factors involved). In the cosmetics industry, standardized tests have been developed to yield the net effect of all aspects of emulsion stability. 

This chapter is focused on kinetic stability in miniemulsions with emphasis on the coupled destabilizing subprocesses, in distinction from other chapters in the Encyclopedia describing other aspects of emulsion stability. 

Above we have presented various applications of the NMR technique in the study of emulsions. NMR is a versatile spectroscopic technique. This is also reflected in the span of questions pertaining to various aspects of emulsions that can be addressed with the NMR technique. The topics covered above include the determination of droplet size distributions, aspects of emulsion stability, crystallization of fat, and medical imaging. 

From the discussion above, it is clear that, from a surface chemical point of view, one aspect of emulsion stability is of primary importance—the protection of the emulsion droplets from coalescence. As a result, that area has received the greatest... 

The coalescence of liquid droplets, therefore, is intimately related to the nature of the thin lamellar film formed between them as they are brought into close encounters as a result of thermal convection. Brownian motion, or mechanical agitation. It is important to understand the nature of the forces acting across the film in order to obtain information about the thermodynamic stability, metastability, or instability of the film, and the kinetic processes that will control the rate of film breakdown. Comprehensive reviews of those aspects of emulsion stability can be... 

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