Chapter 3 105 gels or emulsions using either ceto-stearyl trimethylammonium chloride or distearyldimethylammonium chloride as cationic surfactants and ceto-stearyl alcohol as co-surfactant. As a primary surfactant, the vast majority of conventional conditioners contain either cetyl/stearyl trimethylammonium chloride or distearyldimethylammonium chloride. The secondary surfactant is most often ceto-stearyl alcohol. Cetyl/stearyl trimethylammonium chloride is a conical molecule according to Ninham’s packing factor. On the other hand, ceto- stearyl alcohol consists of molecules with the approximate shape of an inverted conical molecule. The role of ceto-stearyl alcohol in a conditioner is to pack between the cationic cones and convert the micellar structure into a lamellar structure with just enough curvature to form a vesicle. Distearyldimethylammonium chloride spontaneously forms vesicles in the presence of salt, and therefore there is usually no need to add a long-chain alcohol to conditioner formulations based upon distearyldimonium chloride. These products form a gel matrix that confers conditioning benefits from rinse-off products. They have been the basis of hair conditioners for the last half-century and they do provide excellent detangling, wet- and dry-combing, and good anti-static properties, but they can leave the hair feeing lank and greasy, and they give a long-lasting slippery feel during rinsing which is perceived by some consumers as unclean hair feel. Pristine hair, as it emerges from the scalp, is coated with a covalently bound layer of 18-methyleicanosoic acid (18-MEA).90-92 It has been shown that the layer of 18–MEA confers hydrophobicity and boundary lubrication on hair fibers.93 This discovery has influenced researchers to seek to include 18-MEA in conditioner formulations.94 Pristine hair shows a measured advancing water contact angle that is high, but a receding contact angle that is likewise high, and the hair tends to align. However, once the 18-MEA layer is removed, the receding contact angle is low (even approaching 0 degrees), and this corresponds to cuticle edges that are essentially hydrophilic. This means that the major differences
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