Stability of Emulsions

Most emulsions are made up of oil, water, and a third agent -- an emulsifier -- to help stabilize the system. This emulsifying agent, or surfactant, stabilizes the emulsion by affecting its electrical charge, interfacial tension or physical barrier.

How do emulsifiers work? Effective emulsifiers contain both a hydrophilic and hydrophobic portion of the active substance in the emulsion.

HLB Numbers
0-6	water/oil emulsifier
8-20	wetting agent
12-18	oil/water emulsifier

Because these factors impact effectiveness, emulsifiers are categorized on the basis of an HLB number. Most emulsifiers have an HLB number between 12 and 18, which refers to an oil-in-water emulsion. Such an emulsion is more hydrophilic than hydrophobic.

The emulsifiers or surfactants may serve as a barrier between the two phases. They may also lower the surface tension of one phase more than the other. For example, in most food emulsions, the surface tension of oil is higher than that of water. However, a strong hydrophobic surfactant allows non-polar oil to spread and flow around the water droplet with the higher surface tension, as the surfactant lowers the surface/interfacial tension of oil to a greater degree.

While an emulsified system may appear simple, as you can see in the photo, it is actually quite complex. Click on Back.