Applications of Surfactants in Emulsion Formation and Stabilisation

Emulsions are a class of disperse systems consisting of two immiscible liquids. The liquid droplets (the disperse phase) are dispersed in a liquid medium (the continuous phase) [1]. Several classes may be distinguished oil-in-water (O/W), water-in-oil (W/0) and oil-in-oil (0/0). The latter class are exemplified by an emulsion consisting of a polar oil (e.g. propylene glycol) dispersed in a non-polar oU (paraffinic oil) and vice versa. 

To disperse two immiscible liquids one needs a third component the emulsifier. Emulsions may be classified according to the nature of the emulsifier or the stmc-ture of the system (Table 6.1) [1]. 

On storage, several breakdown processes may occur that depend on the particle size distribution and the density difference between droplets and the medium. It is the magnitude of the attractive versus repulsive forces that determines flocculation. The solubility of the disperse droplets and the particle size distribution determines Ostwald ripening. The stability of the liquid film between the droplets determines coalescence phase inversion [1]. The various breakdown processes are illustrated in the figure 6.1. 

The physical phenomena involved in each breakdown process are not simply described, requiring analysis of the various surface forces involved. In addition, the 

Simple molecules and ions Nature of intemal and external phases 

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I 6 Applications of Surfactants in Emulsion Formation and Stabilisation Tab. 6.4. HLB group numbers. 

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