What Sets Cationic Surfactants Apart
Cationic surfactants, as their counterparts, are quite 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 a salt via addition of small amounts of weak acids, such as citric, lactic, or propionic to form the corresponding ester (stearamidopropyl dimethylamine lactate). These neutral 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 quite 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, facilitating deposition of 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, due to their surfactant structure, 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.
Alkyl-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
Alkyl amines or amine salts:
- Stearamidopropyl dimethylamine (lactate, citrate, propionate)
- Isostearamidopropyl dimethylamine
- Isostearamidopropyl morpholine
- Wheatgermamidopropyl dimethylamine
- Behenamidopropyl dimethylamine