Other Influences on Emulsion Stability

An assessment of emulsion stabUity involves the determination of the time variation of some emulsion property such as those described in the physical characteristics section earlier. The classical methods are well described in Reference [47]. Some newer approaches include the use of pulse nuclear magnetic resonance or differential scanning calorimetry [48]. 

Two additional stabilizing influences will be summarized next that of viscoelastic films and that of solid-particle films. In general, where electrical surface charge is an important determinant of stability, it is easier to formulate a very stable O/W emulsion than a W/O emulsion because the electric double layer thickness is much greater in water than in oil. (This is sometimes incorrectly stated in terms of greater charge being present on droplets in an O/W emulsion.) However, there are ways to effectively stabilize W/O emulsions. 

The most stable Pickering emulsions occur when the contact angle is close to 90°, so that the particles will collect at the interface. Combining Young s equation with 

In food science, ice crystals play a role in stabilizing ice cream, while fat crystals play a role in stabilizing whipping cream. It should be emphasized that in practice the contact angles should neither be too high nor too low, or else the partides will remain in the water or oil phases, respectively, and not stabilize an emulsion [297]. Although there are many exceptions to such rules they remain useful for making initial predictions. The particles used for emulsion stabilization have to be much smaller than the size of the emulsion droplets they are intended to stabilize so the particles are usually quite small, typically less than 1 pm in diameter. 

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