In many industries, the challenge of making high quality submicron emulsions has never been more important. Fine emulsions make excellent carrier systems for a wide variety of active ingredients. Depending on the application, they improve texture, aesthetics, taste, rheology, shelf-life, or even cost. In short, the quality and stability of emulsions play a major role in refining the physical characteristics and effectiveness of numerous end products.
In an emulsion, big and small drops of the dispersed phase coexist throughout the continuous phase. The size distribution of these suspended droplets gives the best description of the emulsion and affects both stability and viscosity. Generally, the smaller the average particle size and the tighter the size distribution, the more stable the emulsion. This trend is relatively consistent among most emulsions whatever the end use and application; however there is no ideal droplet size that applies to all formulations. In other words, a 0.5-micron average droplet size may be considered a very stable level for one emulsion but not for another.
Sufficient mixing energy is required in order to create small droplets in an emulsion. For most systems, shear level has a direct relationship to droplet size reduction, but only within a specific limit. Many emulsions are shear-sensitive such that droplets start to coalesce beyond a certain level of shear. Apart from mixing intensity, several other factors affect emulsion stability including inherent properties of the dispersed phase and the continuous phase, temperature, presence and type of surfactant, etc.