Surfactants — Heroes and villains of a skincare routine Part 1: What the heck is surfactant?
Can you imagine the world without cosmetics?
This is what would happen if surfactants didn’t exist. They represent a large group of ingredients and could be found in the majority of products we apply on our skin. Surfactants are crucial to cosmetic formulations.
I’ve put together a short series of articles which will give you some insights how surfactants work; it will help you to recognize them on labels and compare the most common ones in cosmetic formulations. Finally, we will take a closer look on micelles and micellar cleansers as an example of surfactant goodness. I promise to limit the chemist lingo as much as possible.
As the title says, in this part, we will focus on explaining, what are surfactants and what are their main features. Let’s get bubbles going!
It all starts on the surface
There is something called surface tension — a physical phenomenon occurring between two substances: liquid and solid, liquid and gas or liquid and other liquid. It makes the surface of this first liquid behave like a resilient membrane. All because of micro-forces making the liquid molecules stick together like a football players huddle. That’s why water splashes form droplets instead of spreading single molecules around.
Very special agents
The Happy community of cuddly molecules lasts as long as we don’t add the substance called surfactant (contraction of Surface Active Agent). This ingredient not only decreases the forces between molecules on the surface of the liquid but also rearrange them, and gives entire substance brand new properties.
Surfactant molecule has a unique structure which allows them to dissolve in two different solvents simultaneously. Something like yin-yang of chemistry, where one molecule has two opposite sides/groups:
1
Hydrophobic — attracted to fat but avoids water (phobic from “phobia” which means aversion to something)
2
Hydrophilic — loves water but doesn’t dissolve in fat (-phillic from “philia”- affection to something)
When you pour surfactant into a liquid containing both fat and water, surfactant molecules gather on the surface aligning “water-loving” part in water and oil-loving part in oil. In nutshells — Surfactants work like chemical organizers.
Now the trickiest part
Obviously, not all the surfactants are the same and chemists divided them into four groups. This classification is based on the electric charge of the “water-loving” part of a surfactant molecule. Positively charged substances are “pushed” away from other positively charged substances, but are attracted to negatively charged ones. This quality on the molecular level has a tremendous impact on surfactants interactions with other substances.
We can distinguish here the following types of surfactants:
1
Nonionic — No electric charge. They are the most often used group of surfactant in cosmetic formulations. Nonionic surfactants work very well with other surfactant categories and are very gentle for the skin.
2
Anionic — Negatively charges molecules. Those surfactants are very common on the market due to low cost and effort of production. They are very reactive with other ingredients.
3
Cationic — Positively charged. Cationic surfactants don’t combine well with anionic surfactants but have the ability to attach to damaged hair or skin proteins. This characteristic makes cationic surfactants harder to rinse off and help them to deliver a nourishment to the cells.
4
Amphoteric — Both negatively and positively charged; often called as zwitterionic which means hermaphrodite in German. They are often used as secondary surfactants and have gentle or even soothing properties. They can change their properties depending on the PH level. In a low PH/acidic environment, they become great skin nourishing agents. In high PH/ alkaline products the bump up the foaming process.
What Surfactants can do
The significant majority of cosmetics wouldn’t be able to exist without surfactants and here is their list of their super powers:
Cleansing (detergency) — the Hydrophilic head dissolves in water and the hydrophobic end in a dirt. The result is an emulsion that is insoluble in water so that it can be easily removed by washing with water, such as rinsing our hands with a stream of water under a tap. Used in: shampoos, cleansers, soaps.
Detergent or surfactant? Many people use those two expressions interchangeably, but in fact, they are not the same. Word surfactant represents only one chemical compound. A detergent is a final product, for instance, a washing liquid — the mixture of surfactants and other properties enhancing additives such as fragrances and coloring.
Foaming — Foam is formed when a gas is added to the surfactant solution, such as air. Air has a lower density than the liquid and is trying to escape causing surfactant molecules to form thin films at the liquid-air interface, seen as a form of bubbles. Used in: Shaving gels and foams, bath products, shampoos, face cleansers, soaps.
Emulsifying — Emulsification is the process of combining two immiscible and insoluble liquids, such as water with oil. In result water + oil forms emulsion — a suspension of droplets of one liquid in another. This arrangement is very unstable, and both liquids separate right after the intense mixing is stopped unless we add emulsifiers — surfactants which keep both types of liquids evenly blended for longer periods of time or even for good. Used in: creams, serums, lotions, conditioners, foundations, makeup products and gentle cleansing products.
Moisturizing (Wetting) — When we add a surfactant to water the intermolecular forces become weaker making the water molecules less attached to each other. As a result, they become more “independent” and can easily penetrate surfaces with pores such as human skin. Used in most cosmetics.
Preservatives — These surfactants are used to protect cosmetics from contamination with germs. They kill bacteria by breaking the lipid membrane protecting their cells. Used in: the majority of cosmetics which contain water — ideal environment for bacteria growth.
Thickening — In this case, one surfactant “cooperates” with substances such as salts, polymers or other surfactants. Those extra ingredients help this main surfactant to form a stable mesh which locks particles into place and changes the nature of the products from liquid to more solid. Used in creams, lotions, conditioners, shampoos, cleansing products, mascaras and other makeup products.
Opacifying — some surfactants can lower the absorption of light in certain substances and as a result, change them into more opaque. This feature is especially important in makeup products and gives the better covering properties but also in cleansing products which are advertised for instance to mimic milk.
Conditioning — The surfactants form a rinse resistant film (as mentioned in Cationic surfactants) on the surface of the skin which not only protects it from water loss but also can bring along other nourishing substances. Used in: creams, lotions, conditioners, cleansers makeup products.
So, we’ve gotten this far with Part 1 of this Surfactant series. Stay tuned for the next post — Part 2, in which we will call out the “the good, the bad and the ugly” among most common surfactants in cosmetic formulations.
References:
http://www.essentialchemicalindustry.org/materials-and-applications/surfactants.html Date Accessed, May 30th, 2017
http://www.pcc-exol.eu/bazy/surfactants.nsf/id/PL_Surfaktant_-_budowa_i_wlasciwosci Date Accessed, May 30th, 2017
http://chemistscorner.com/what-kinds-of-surfactants-are-used-in-cosmetics/ Date Accessed, June 1st, 2017
http://biotechnologia.pl/kosmetologia/surfaktanty-kontra-biosurfaktanty,14731 Date Accessed, June 1st, 2017
http://okiemkosmetyczki.blogspot.ca/2013/04/surfaktantyczyli-srodki-powierzchniowo.html Date Accessed, June 1st, 2017
http://naukowo.blogspot.ca/2013/09/surfaktanty-kationowe.html Date Accessed, June 1st, 2017
http://www.thermopedia.com/content/1174/ Date Accessed, May 30th, 2017
http://swiftcraftymonkey.blogspot.ca/2011/02/fun-with-chemistry-anionic-cationic-and.html Date Accessed, May 30th, 2017
