What is an emulsion?

An emulsion can be defined as a dispersion of one material (usually the oil phase) inside another non-miscible (water) phase. However this is not a natural state – J W Gibbs, On the equilibrium of heterogeneous substances (1878), stated that “the only point in time where an emulsion is stable, is when it is completely separated”. As an emulsion will eventually separate over time, our aim is delay this separation for as long as possible.

Simple emulsions are either oil suspended in a water phase (o/w), or water suspended in oil (w/o). The emulsifier we choose determines whether the emulsion will be o/w or w/o. Most emulsions we make are o/w which are generally, more stable and easier to formulate, and this is the type of emulsion we will be discussing in this article.