Article by: Perry Romanowski
We’re starting a new feature here on Chemists Corner. It’s called cosmetic science in 300 seconds. It will be a 5 minute video that will quickly explain some aspect of cosmetic science, formulating, testing, or any other cosmetic formulator appropriate topic. To kick it off, here is Surfactants in 300 Seconds.
Welcome to Cosmetic Science in 300 seconds brought to you by Chemists Corner.
Today’s topic is surfactants.
Surfactants are one of the most important types of ingredients used in the formulation of cosmetic products. You’ll find them in cosmetics ranging from body washes to skin lotions to eye shadows to toothpaste. Almost every cosmetic you use contains at least one surfactant.
Surfactants have been used by people since the invention of soap back in 2800 BCE. But it wasn’t until late 19th century when sulfonated castor oil was used in the textile industry as a dyeing aid that synthetic surfactants were made. In the 1920’s & 30’s surfactants from long-chain alcohols were created and in the 1950’s and 60’s most of the synthetic surfactants that we use today were introduced.
Some commonly used surfactants include Sodium Lauryl Sulfate, Cocamidopropyl Betaine, and Glyceryl Stearate.
The term surfactant stands for Surface Active Agent. This refers to the fact that in solutions, surfactant molecules migrate to the surface and align themselves in a manner which reduces surface tension.
The reason surfactants behave in this manner is because of the way their molecule is structured. A portion of the molecule is hydrophilic (or water loving) while another portion is hydrophobic (or water hating). You might also hear them refered to as lipophilic (oil loving) or lipophobic (oil hating).
When a surfactant is mixed with water, the hydrophobic parts of the molecule align themselves as far away from the water as they can. Simultaneously, the hydrophilic portion of the molecule continues to be attracted to the water. This leads to a variety of different molecular arrangements such as monomers, spherical micelles, tubules, rods, lamellar sheets, and bilayers. The exact structure depends on the type and concentration of surfactant in the solution.
Normally, when oil and water are put together they do not mix nicely but rather stay separated. You can see this in salad dressings. This is because polar materials like water are more compatible with other polar materials while nonpolar materials like oil are more compatible with nonpolar materials. This has led to the general adage in chemistry “like dissolves like”.
The unique surface properties of surfactants mean that they can be compatible with both the oil phase and the water phase of this solution. This leads to a number of useful applications in cosmetics.
Cleaning – First, surfactants are useful whenever you want to make something that will clean a surface. Water will remove all the water compatible ingredients, but for nonpolar dirt and oil, you need a surfactant to help remove it. These surfactants are called detergents and are found in shampoos and body washes.
Incidentally, surfactants have the added bonus of making foam. Lots and lots of foam.
Emulsions – Since the materials that are useful for cosmetics can be both polar and nonpolar materials, surfactants can be employed to create a mixture that has both. When surfactants are blended into these mixtures they align themselves in the solution to create small particles called micelles. Upon mixing, the particles are dispersed throughout the solution creating an emulsion. Emulsions are the basis for nearly all creams and lotions.
Moisturizing – Some surfactants can attach to the surface of skin and hair to improve the look and feel so they are frequently added to moisturizing and conditioning cosmetics. Hair conditioners and skin moisturizers usually contain one or more surfactants.
Aesthetic modifications – Typically, people who use cosmetics want them to be thick or opaque and easy to spread. For cosmetic formulators to create these effects, surfactants such as fatty alcohols can be used.
Preservatives – Finally, some surfactants have one more characteristic that makes them useful in cosmetic products. They can disrupt the structure of cell walls which means they are able to destroy any disease causing microbes that might grow in the cosmetic. This makes them useful as preservatives.
As you can see surfactants have a wide range of application in cosmetic formulas. The technology has not changed much since the late 1960’s but cosmetic raw material manufacturers continue to try to improve. In the future, surfactants promise to be less irritating, more efficient and produced from more sustainable starting materials.
This brings us to the end of Cosmetic Science in 300 Seconds. If you want to learn more about cosmetic science and formulating please visit our website Chemists Corner.com. I’m Perry Romanowski, thanks for watching.