Surfactant Surface Tension

Lately, I have been getting a wee bit technical, which is important if you want to know how lovely surfactants create all that foam.

Surfactants are typically used in foaming and cleansing agents, they are popular because they’re effective at generating lather within personal care products.

They often take the form of detergents in everything from dish wash liquid to body wash and face wash, they work by pulling both oil and water together so that when you rinse the product away, the oil is also eliminated.

The main point here is that they represent a large group of ingredients in many products, so how they are used varies: for some beauty products, they act as a detergent, for others as a solubiliser, for others as an emulsifier.

In other words, they’re a group of chemicals designed to interface oil with water, within a range of applications.

What are surfactants?

In cosmetic chemistry, soap surfactants are known as surface-active ingredients, they all work on the same basic principle – that everything in nature is either water-loving or oil-loving.

These surfactants are made up of long molecules and each end of these molecule plays a different role:

  • Hydrophilic, which means that they are water-loving
  • The Lipophilic molecule is oil-loving
  • Hydrophobic meaning it repels water

The most common sulfate ingredients, which are sodium lauryl sulfate (SLS) and sodium laureth sulfate (SLES), which I discuss here. While both of these ingredients do their job really well — they’re well known to cause side effects, including eye and skin, inflammation and irritation, which can lead to premature ageing over time.

This is because sulfates can strip the skin’s natural barrier function, resulting in increased water evaporation – referred to in the industry as transepidermal water loss (TEWL). The skin becomes undermined and has limited protection from environmental assaults causing serious dryness. In effect, they’re almost too efficient at removing oil from your skin, leaving you with a lipid deficiency that will exacerbate ageing and inflammation.

Understanding surfactant surface tension

So, what exactly does surfactant surface tension really mean? In layman’s terms, if you look at the structure of a shower gel, the dirt and oils from the skin stick to the lipophilic end, they are lifted off the skin and washed away by the hydrophilic end of the molecule.

From a technical viewpoint, hydrophilic substances can easily dissolve in water – the lipophilic substances will rapidly dissolve in hydrocarbons – these are the essential organic compounds of carbon and hydrogen, it is these hydrocarbons that have a real affinity with oil and dirt.

The usual job of detergents is to make lipophilic substances like oils and grease soluble in water, so they can be easily rinsed from the skin.

The lipophilic end of the molecule the hydrocarbons literally bury themselves into the oil, and when enough of the molecules embed their hydrocarbon ends into the oil, the surrounding water molecules that are attracted to the part of the molecule that likes water breaks down the oils into small pieces, this action then causes it to separate and dissolve, carrying away the grease.

So, as you can see, the role of surfactants on the skin is extremely interesting, and if you’d like to find out more about the role of surfactants, follow the link to find out more.

References

https://www.biolinscientific.com/blog/what-are-surfactants-and-how-do-they-work
https://pubs.acs.org/doi/10.1021/la5030586
https://www.sciencedirect.com/science/article/pii/S0001868617305250

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