Q: Is cetrimonium chloride a silicone? If not, what is it and what is its purpose in my hair-care product? When this ingredient appears on a label with amodimethicone and trideceth-12, does this mean the amodimethicone is now water soluble?
A: This question comes up frequently, because something about that name seems similar to some of the names seen for different silicones. The actual chemical name of this ingredient is cetyl (hexadecyl, more properly) trimethyl-ammonium chloride (CTAC). It is definitely not a silicone or silicone derivative. It is a quaternized ammonium molecule (frequently abbreviated as quat), and it has a single positive charge at the head group. CTAC belongs to a family of molecules known as cationic surfactants, which can be used as emulsifying or conditioning agents. Some other commonly used molecules in this group are cetrimonium bromide (CTAB), behentrimonium chloride, and quaternium-15.
Their conditioning capabilities are due to electrostatic attraction between the positively-charged head group of the cationic surfactant and negative charges that occur along the surface of hair strands. This electrostatic attraction causes cationic surfactant molecules to deposit themselves onto the cuticle of the hair, which helps create a smoother surface and also reduces static-induced flyaway hair that can occur in cold, dry weather.
As emulsifying agents, cationic surfactants can be used to aid the formulator in getting many different types of hydrophobic (water fearing) oils to go into solution. They are frequently used in mixtures with a nonionic surfactant. These mixtures can form large micelles, or emulsion droplets. Oil-in-water micelles are clusters of molecules with an oily center or core, made up of the non-polar tails of the surfactants, surrounded by an outer shell formed by the polar portion of the molecule. The polar portion of the shell is water soluble, and the interior of the micelle can encapsulate a water-insoluble oil, such as silicone. This complex particle can then be dispersed into an aqueous solution, such as a hair conditioner or shampoo formula. (There are also micelles known as water-in-oil micelles, where the polar groups are in the interior portion of the micelle, and the oil soluble portions are on the exterior of the micelle.)
A common example of such a mixture is cetrimonium chloride, trideceth-12 (the nonionic surfactant), and amodimethicone. The two surfactants surround the amodimethicone, which is water insoluble. The resultant aggregate of all three components is dispersible in water, due to the hydrophilic nature of the micelle shell. However, it should be noted that this mixture is dispersible in water for the purposes of ease of manufacture of the shampoo or conditioner. The mixture does not remain intact during product use, and it should not be inferred that having those three components in a formula renders the amodimethicone water soluble once it is applied to the hair.
Once the actual product is applied to wet hair in the shower, the aggregate is broken up and each component does what it would ordinarily do. The nonionic surfactant is washed away when the hair is rinsed; the positively-charged amodimethicone and the cationic surfactant are each deposited (separately) onto the surface of the hair. The amodimethicone is left alone, and is thus in its water insoluble state, and it dries to form a film, which imparts sheen and silkiness to the hair. Despite the fact that it is water insoluble, amodimethicone has been found to resist the formation of build up, and most users have reported excellent results with products containing amodimethicone, even if they use a shampoo-free regimen.