Cosmetic emulsion theory and technology

Definition and types
Dispersions are mixtures of two immiscible phases, in which one phase is evenly dispersed in the other. The phases may be gas, liquid or solid. The phase that is dispersed is generally 1 micron in diameter and is referred to as the internal phase, while the phase that envelops the dispersed phase is called the external or continuous phase. Table 1 below describes the name and examples of common dispersion types. Dispersions with particle size between 1 nm and 1 micron are sometimes referred to as “colloids”. The term emulsion is more specifically used to describe those dispersions that involve liquids. A typical example is cream in which oil is mixed evenly in water. Figure 1 represents an emulsion. There are three main types of emulsion:

•  Oil-in-Water (O/W)
•  Water-in-Oil (W/O)
•  Multiple (W/O/W) or (O/W/O)

The internal phase ratio, or IPR, is the fraction of internal phase within the total emulsion, also called “phase volume”. We can categorise the internal phase ratio as low (<30%), medium (30%-70%) and high (>70%). Examples of such emulsion include a “milk”, “cream” and “mayonnaise” respectively. Standard emulsions generally have a droplet size in order of 1 micron. Microemulsions and nanoemulsions have droplet sizes between 1 nanometer and 1 micron.