The Science Behind Hair Products

April 23, 2012

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)

These materials are typically incorporated into shampoo formulations for their detergency properties.
They are highly effective at removing dirt and oil from the hair and scalp.
Many consumers with delicate, curly hair find these to be too drying and damaging for frequent use, and they either seek shampoos with different types of surfactants or opt to use cleansing conditioners.

Nonionic surfactants (such as decyl glucoside and PEG-10 laurate)

Have no residual electric charge at all.
These surfactants can perform a variety of functions in a formula, such as emulsion stabilization and mild detergency.

Zwitterionic (or amphoteric) surfactants

Have a positive and negative charge on the molecule).
These types of surfactants, such as cocamidopropyl betaine, are valued for being mild both to skin and hair.
They also provide foam-boosting to shampoos that contain anionic surfactants, which enhances lather, a property preferred by many consumers.

WHAT SETS CATIONIC SURFACTANTS APART

Cationic surfactants, as their counterparts, are versatile due to their amphiphilic character. However, rather than being used primarily for detergency, cationic surfactants are more often used for very different applications, especially in hair care products. Perhaps the most important use for cationic surfactants in hair care is as conditioning agents.You may recall that the surface of hair has an overall negative charge, which becomes more prevalent if the cuticle is damaged. The head groups of these cationic surfactants experience electrostatic attraction to these negatively-charged sites and adsorb onto the surface of the hair.

The hydrophobic portion of the surfactant molecule lies flat along the surface of the hair, forming a film that smoothes the cuticle. This film has multiple effects, including reduction of static, reduction of combing forces, increase in pleasing tactile feel of the hair, and a decrease in tangle formation. Cationic surfactants used for these purposes have also been found to aid in color retention for artificially dyed hair.

Alkyl quaternary ammonium salts (such as cetrimonium chloride and behentrimonium methosulfate) have been found to build up on the surface of hair after multiple uses. They can be rather difficult to remove once this happens. They are also incompatible with anionic surfactants in shampoos, as they form an insoluble complex in the solution. Another undesirable property for use in shampoos is that they depress the foaming ability in such formulae. For this reason, they are most preferred in conditioning products.

Alkyl amine salts (such as stearamidopropyl dimethylamine) actually adsorb onto the surface of the hair to a lesser extent than he quaternary compounds. They are also more easily rinsed and removed, and thus have less incidence of undesired accumulation. Alkyl amines can be neutralized into salts are quite compatible with anionic surfactants and do not interfere with foam formation, rendering them quite suitable for use in conditioning shampoos.Cationic surfactants are also useful for the emulsification and solubilization of hydrophobic additives, such as silicones.

They achieve this by encapsulating the non-polar material inside the interior of their micellar structures. Once the solution is diluted by water in the shower, the micelle structures break down, depositing the conditioning agent onto the surface of the hair. This enables them to perform multiple functions in the same formula; emulsion stabilizer as well as conditioning agent.

Overall, cationic surfactants contribute many excellent properties to both shampoos and conditioners. They can be effective mild cleansers in a conditioner, but their most valuable contribution is as film-forming conditioning agents. They are water soluble, but the quaternary variety bind rather tightly to the hair surface and can build up, so be aware of the potential for that issue. The alkyl amines seem to have no significant drawbacks for a curly girl or guy, and many users report enjoying their effects.

Quick Round-UpAlkyl-quaternized ammonium salts:

Stearalkonium chloride
Cetrimonium chloride
Cetrimonium bromide
Behentrimonium methosulfate
Behentrimonium chloride
Benzalkonium chloride
Cinnamidopropyltrimonium chloride
Cocotrimonium chloride
Dicetyldimonium chloride
Dicocodimonium chloride
Hydrogenated Palm Trimethylammonium chloride
Lauryltrimonium chloride
Quaternium-15
Quaternium-22
Stearamidopropyl dimethylamine (lactate, citrate, propionate)
Isostearamidopropyl dimethylamine
Isostearamidopropyl morpholine
Wheatgermamidopropyl dimethylamine
Behenamidopropyl dimethylamine

Alkyl amines or amine salts:

Stearamidopropyl dimethylamine (lactate, citrate, propionate)
Isostearamidopropyl dimethylamine
Isostearamidopropyl morpholine
Wheatgermamidopropyl dimethylamine
Behenamidopropyl dimethylamine

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