If you've ever dived deep into what's behind your hair products, you may have encountered several cationic surfactants, such as cetrimonium chloride, behentrimonium methosulfate and stearamidopropyl dimethylamine. That's a mouthful!
For good reason, the INCI (International Nomenclature of Cosmetics Ingredients) names of these molecules are often confused with silicones, sulfate detergents and preservatives. It can be surprising to hear that a “sulfate” is a desirable conditioning agent for many people. A review of the different types of surfactants and a closer examination of cationic surfactants brings some clarity to the confusion.
WHAT ARE SURFACTANTS?
Surfactants are molecules that have dual-polarity, both hydrophobic (water hating) and hydrophilic (water loving) segments. Although hydrophobic is the term most often used to describe non-polar substances, the term lipophilic (oil loving) is maybe a more accurate descriptor, because they do not so much hate water as they prefer oils. The unique quality of being both lipophilic and hydrophilic is described as being amphiphilic.
Due to the uniquely polar properties of water, immersing an amphiphilic molecule in an aqueous solution results in very interesting behavior. Water molecules have strong intermolecular hydrogen bonding that creates a predictable geometric structure within the bulk of the liquid. This hydrogen bonding forms a tightly stretched molecular film at the interface between air and the liquid. This gives water its characteristically high surface tension. Placing a molecule with hydrophobic properties into that environment disturbs that structure, so the water excludes the hydrophobic molecule from the solution by pushing it to the surface.
You have certainly witnessed this yourself when you have seen the rainbow display of oil on the surface of a water puddle. When the molecule has both a hydrophilic portion and a hydrophobic portion, this disrupts the hydrogen bonding at the surface of the water, which substantially decreases the surface tension. And so, amphiphilic molecules are said to be “surface active agents” and called surfactants.
Eventually, if the amphiphilic material is increased, the surface of the solution becomes saturated, and an intriguing phenomenon occurs. In order to preserve as much of the polar structure of water as possible, the amphiphile molecules aggregate together into tiny spheres in the bulk of the solution calledd micelles. They're the foundation for many biological functions, and useful for many functions such as cleansing and drug release.
TYPES OF SURFACTANTS
Surfactant molecules are classified according to the ionic charge of the hydrophilic head group. These classes consist of anionic, cationic, nonionic, and zwitterionic surfactants. Let's take a look.
Anionic surfactants, (such as sodium lauryl sulfate, ammonium laureth sulfate and sodium cocoyl isethionate)
Nonionic surfactants (such as decyl glucoside and PEG-10 laurate)
Zwitterionic (or amphoteric) surfactants
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