ABSTRACT
Traditionally, emulsions have been defined as dispersions of macroscopic droplets of one liquid in another liquid, with a droplet diameter approximately in the range of 0.5-100 μm. However, one must realize that most emulsion formulations used in practice are more complicated. This fact made the International Union of Pure and Applied Chemistry formulate the following definition of an emulsion: “In an emulsion liquid droplets and/or liquid crystals are dispersed in a liquid”. An emulsion is formed when two immiscible liquids are mechanically agitated. During agitation, both liquids tend to form droplets, but when the agitation ceases, the droplets separate into two phases. For emulsions with significant stability and with moderate phase ratios, the type of emulsion is decided by several factors, such as the order of addition or the type of emulsifier. The most common types of pharmaceutical or cosmetic emulsions include water as one of the phases and oil or a lipid as the other.
