Clear dispersions of oil in water or water in oil are called microemulsions. The disperse phase globules are very small, ranging in diameter from 100A° to 600A°. These emulsions appear as transparent solutions and are more acceptable physically as compared to conventional emulsions.

Self-emulsifying Systems

These are anhydrous products that when added to excess of water form emulsions spontaneously without requiring too much agitation. These systems are known as self-emulsifying drug delivery systems (SEDDS) and can be formulated by the use of a combination of hydrophilic and lipophilic surfactants.

Complex Emulsions (Multiple Emulsions)

1. W/O/W emulsions: An oil droplet enclosing a water globule may be dispersed in water to give W/O/W emulsions; see Fig. 6.2(a).
2. O/W/O emulsions: A water droplet enclosing an oil globule may be dispersed in oil to give O/W/O emulsions; see Fig. 6.2(b).

Figure 6.2 Complex Emulsions (a) W/O/W Emulsion (b) O/W/O Emulsion