Lets Mix Oil and Water

Happy New Year faithful readers!
Let's bring in 2013 with more about the chemistry behind cosmetics.
Expect more posts in the coming year with more of an emphasis on the chemistry that takes place in manufacturing of cosmetics. :)

Today we're going to talk about emulsions:

Listen to this helpful podcast from BASF "The Chemical Reporter" to get some background information on emulsifiers

Emulsifiers, or surfactants are molecules that have special properties. They contain two parts: one that can dissolve in water (the hydrophilic end) and one that can dissolve in oil (the hydrophobic end). You will see this structure again in our upcoming blogpost on soaps and saponification, so keep it in mind.

Basic structure of an emulsifier

Emulsifiers are used to reduce the tendency of oil and water to separate into layers by forming an emulsion. An emulsion is formed when tiny droplets, called micelles, of one liquid are suspended in a another liquid.
Emulsifiers change the surface properties of liquids. The hydrophobic tail of these molecules burrows into the oil, leaving the exposed hydrophilic head out to bind to water molecules. When the oil and water mixture is agitated, micelles will form.

What do emulsions look like?

Emulsions usually have a cloudy appearance, because of all the different phase interfaces, which are the layers between two different phases, and in this case, the two different immiscible liquids. When you just have oil and water in a cup, the oil and water form two separate layers, with one interface, between them. However, when you add an emulsifier, and mix them together, small micelles will form with interfaces around each micelle. All these interfaces scatter light as it passes through the emulsion, giving it a cloudy appearance.

Emulsions appear white when all light is scattered equally, but if an emulsion is dilute enough, there are less micelles in solution and shorter wavelength light will be scattered more, making the emulsion appear more blue. If the emulsion is concentrated enough, longer wavelengths will scatter more, and the emulsion will be yellower. An example of this would be skimmed milk, compared to creams. Speaking of creams, comparing the creams that are used for skincare to just lotion (provided there is no artificial coloring) will also demonstrate this effect.

But why are emulsions important in cosmetic chemistry?

The majority of Skin Care products and a very significant percentage of toiletry products are emulsions. The basic components of these formulations are emulsifiers, emollients, and consistency enhancers. The chosen emulsifier for a product is not only crucial for the stability of an emulsion (and thus the preventing of separation, which no one wants), but also has a large impact on consistency, skin feel, and care properties of a formulation. Emulsifiers have a wide range of applications in cosmetic products. They are used in creams, lotions, sprays, and foams.

For the purposes of this blog post, we will be focusing on the emulsions of creams and lotions, and leave sprays and foams for another blog post.

Here is a helpful table of common emulsifiers used in cosmetic products:

What we've talked about so far is nice, but lets delve deeper, and look at the thermodynamics of emulsions. Stay posted for the second part of the blog post, to be published on January 11th

jennymu