Oil-in-water (0/W) emulsifiers

Oil-in-water (0/W) emulsifiers

- Anionic O/W emulsifiers

Anionic 0/W emulsifiers can be used to obtain very stable emulsions because they can build an electrical double layer around the droplets, which prevents the droplets from coalescing. On the other hand, anionic emulsifiers are sensitive to low pH and electrolytes.
The most important anionic 0/W emulsifier is soap, which forms the stearate creams. Neutralized with potassium hydroxide, the stearate is alkaline. The use of triethanolamine as a neutralizing agent is more common. A disadvantage of stearic acid s the typical ‘soap-up’ effect, a type of foaming that occurs when the cream is rubbed into the skin. To prevent this, silicon oil is frequently added to the formulations.
Other very effective anionic emulsifiers are alkyl sulfates, particularly sodium cetearyl sulfate. In principle, all anionic surfactants can be used. However, due to the fact that the soaps are relatively alkaline and fatty alcohol sulfates are irritant to the skin, the mild surfactants are of more interest. These include sodium cocoyl isethionate as an extremely mild emulsifier, and phosphoric acid esters, like potassium cetyl phosphate which are very effective at low concentrations.