Applying a cream or a lotion, have you ever wondered, what is this creamy substance? How does it come that the oils and all these liquid extracts produce this creamy texture, if per se they physically cant mix. The concept behind this is called Emulsion.
It is known that different liquids have differents densities. Oil is less dense than Water. Therefore these two liquids would never mix – oil will remain on the surface of the water as it’s molecules are larger than these of the water. With help of a special agent, an Emulsifier, it is possible to disperse one liquid into another. As a result you have an Emulsion, which is a mixture of two or more liquids in which one is present as droplets, of microscopic size, distributed throughout the other.
Types of Emulsions
In every Emulsion there is a continous phase which suspends the dispersed phase. Therefore there are two main types of emulsions:
Oil in Water-Emulsions
Oil droplets are dispersed in continuous water phase.
Water in Oil-Emulsions
Water droplets are dispersed in continuous oil phase.
So what is this Emulsifier?
Emulsifier is a substance that stabilise emulsion, preventing the Oil and Water parts from separating. The emulsifier molecule consists of two parts:
- the hydrophilic („water loving“ part), that forms chemical bonds with water but not with oils and
- lipophilic („oil loving“ part), that forms chemical bonds with oils but not with water.
When I first started experimenting with emulsions, I made some errors. Especially during the hot summer, some emulsions showed signs of separation between the oil and the rest of the cream. This effect is called Coalescence, where the oil/water droplets tend to bind with the next biggest oil/water droplets until both phases completely separate. Therefore, I want to stress the importance of the following factors for producing emulsions.
Factors needed to produce an Emulsion
The higher the force applied while blending oil and water phases together, the smaller the particles and thereby the more stable the emulsion will be. There are different types of equipment that can be used: from a hand blender to professional lab equipment used also in pharmacies. I will cover this topic later.
To prevent the coalescence effect even further we use a Gelling Agent. The gelling agent is added in the water
phase to create a gel like texture. This makes it difficult for the oil/water particles to move and to intermix. The most commonly known gelling agents, which are also used in gastronomy, are Xanthan Gum and Agar Agar.
Last but not least for a proper and stable formula it is essential to choose the right emulsifier. This depends on what kind of product you want to create: light fast absorbing lotion, fluid or a rich and nourishing cream. The natural cosmetics market offers a wide range of emulsiifers with different characteristics. In the next article I will cover how to choose the right emulsifier for your needs.