As readers of this column certainly must by now know, emulsion stabilization is a favorite topic of mine. A key component of every emulsion is the thickener or, more properly, a thickener system that is employed. We all remember the Stokes Law, which tells us that an important factor in stabilizing emulsions is the viscosity of the external phase. Interestingly enough, often the primary function of thickeners is not to increase the viscosity of the emulsion, but to stabilize the emulsion or to affect application qualities.
The choice of thickeners is almost limitless, with more being developed practically every day. This short column will discuss a few thickeners and things to keep in mind when choosing them. It is by no means comprehensive, and I’m fairly certain that I won’t be discussing your favorite material.
There are a number of factors to be considered when choosing a thickening agent for emulsions, but the most important one is to remember your goal. To say it another way: Why are you using a thickener? Is it to increase the viscosity, stabilize the emulsion, effect application qualities, or suspend some particulate material? In regards to increasing the viscosity, we know that this can be accomplished in two ways: increasing the volume/size/percentage of the internal phase, or increasing the viscosity of the external phase (see previously mentioned Stokes Law).