Friday, 25 March 2011

Water vs. Oil

I read this magazine called Cosmetics and Toiletries Magazine.  Mr. Tony O'Lenick writes this column called compartiatively speaking.  I am a fan of his column and understanding cosmetics in general.  You probably use some sort of cosmetic or toiletry product everyday to wash your hair with a detergent, wash your hands with a soap or apply some makeup to your cheeks.

Did you ever think what all that stuff is in that package?  Some it is preservatives, colorants, maybe some non-medical cosmetic ingredients (aloe vera) and lastly surfactants.  What is a surfactant though?  It is a material that interacts with the surface of the water to break those hydrogen bonds and lower the surface tension of the water.   This is needed in cosmetics as lowering the surface tension of a solvent is a prerequisite for wetting, spreading, foaming and emulsification.   However, not all molecules that lower surface tension will provide all these functions, but to achieve these properties companies want to make a product that can lower the surface tension to achieve these desirable properties.

As mentioned before (and the name of this blog) water has a surface tension of 72 dynes/cm which is relatively high.  It can be lowered into the range of 32–35 dynes/cm with traditional water-soluble fatty surfactants (for some of the ingredients look at the back of your cream). Consequently, properly selected fatty surfactants can wet, foam, emulsify or facilitate spreading in aqueous solutions.

If you have ever put oil in water when washing dishes you notice that oil differs from water in many respects, the most important of which is surface tension. Oil has a surface tension of 30–35 dynes/cm, meaning that oil-soluble fatty surfactants do not provide the desired surface tension reduction for oils. However, as Mr. O'Lenick mentions several classes of compounds can provide surface tension reduction below 30–35 dynes/cm.  These are based upon silicone and its fluoro compounds.

These silicone surfactants can reduce the surface tension of oils to 20-25 dynes/cm.  Fluoro surfactants can reduce this below.  The ability of these surfactants which are amphilphilic molecules (molecules with a water liking head and a water disliking tail) to orient properly at the surface to reduce the surface tension of water and perhaps the oil that is in the water is what formulators want and what we want to put on our skin.  When you are in the bathroom take some time to look on the back of the package and see if there are fluorsurfactants, surfactants or other things in there that help the ingredients work nicely on your body.