Formulation & testing of emulsions

The interfacial tension forces try to keep the two phases separate, the goal in preparing emulsions is to reduce the interfacial tension to promote a more intimate blending of the two phases. This is accomplished in two primary ways – by reducing the viscosity of the internal phase and through the use of chemical additives. Heating the product is the simplest way to achieve a viscosity reduction because most liquids become less viscous when they are heated. The viscosity decrease is usually accompanied by a decrease in the interfacial tension, leading to better emulsification.
A stable emulsion of two immiscible liquids is rare, and often some type of chemical assistance is required. Usually, a chemical that is active at the interface between the two phases is used. Such an additive is referred to as an emulsifier or a surfactant (this stands for surface-active agent). The commercial preparation of most emulsions involves the application of both a chemical emulsifier and a mechanical device, such as a colloid mill or in-line mixer, to produce a dispersed phase with a droplet size small enough to result in a finished product with the desired properties.