Types of Oil-Water Emulsions

Emulsions are one of the most important structures that are prepared specifically for a given application. For example, a day cream (skin cream) has different characteristics and ingredients than a 

FIGURE 1.57 Mixing of oil-water (a) or oil-water + surfactant (b) by shaking. 

Oil-in-water emulsions The main criterion for 0/W emulsion is that if one adds water, then it will be miscible with the emulsion. Further, after water evaporates, the oil phase will be left behind. Thus, if one needs oil phase on the substrate (such as skin, metal, and wood), then one shall use an 0/W-type emulsion. 

Water-in-oil emulsions The criterion for W/O emulsion is that latter is miscible with oil. That means that if one adds the emulsion to some oil, then one obtains a new but diluted W/O emulsion. In some skin creams, one prefers to use W/O-type anulsion (especially if one needs an oil-like feeling after its application). On the other hand, if one needs oil free surface, then 0/W emulsion is preferred. 

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