Surfactant Surface Tension

Lately, we 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 effectively generate lather within personal care products.

They take the form of detergents in everything from dish wash liquid to body wash and face wash.

These clever little ingredients, work by pulling both oil and water together so that when you rinse your product away, the oil is also eliminated.

They represent many ingredients for many different products, from detergents, solubilisers and emulsifiers, so their application varies depending on the product.

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 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 your skin’s natural barrier function, resulting in increased water evaporation – referred to in the industry as transepidermal water loss (TEWL). Your 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 can 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 shower gel’s structure, the dirt and oils from the skin stick to the lipophilic end, they are lifted off your 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 that they can be easily rinsed from the skin. The lipophilic end of the molecule the hydrocarbons literally bury themselves into the oil. When enough of the molecules embed their hydrocarbon ends into the oil, these surrounding water molecules 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.

Conclusion

So, as you can see, the role of surfactants on your skin is extremely interesting, that work on the principle that the lipophilic molecule is oil loving and the hydrophilic molecule is water-loving when in contact with the skin, the lipophilic end which sticks to your skin is washed off by the hydrophilic end.

If you’d like further reading about the role of surfactants on the skin, 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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