Ingredient Profile: Distearyldimethylammonium Chloride

By: Mike Fevola, Johnson & Johnson

Posted: February 3, 2011, from the February 2011 issue of Cosmetics & Toiletries.

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DSDMAC is a waxy, white to off-white or yellowish solid that may be supplied as a powder or as pellets. Potential impurities in the raw material include residual solvent, e.g. isopropanol; NaCl; nonquaternary amines, e.g. methyldistearylamine; and HCl salts or amine oxides thereof. Although DSDMAC is mildly hydroscopic and typically contains up to 4% w/w water, the material is not water-soluble at room temperature. When heated to 48°C or higher, DSDMAC will form liquid crystalline (LC) solutions in water.⁵

Technology and Applications

Unlike most surfactants, DSDMAC has two very large hydrophobic tail groups bound to a single hydrophilic head group. This twin-tailed molecular architecture causes DSDMAC to possess a high critical packing parameter or P value. P describes the effective shape of surfactant molecules and is illustrated by Eq. 1:

Eq. 1     P = v /a_o • l_c

where v is the volume of the hydrophobic tail group, a_o is the area of the hydrophilic head group, and l_c is the length of the hydrophobic tail group.⁶ P values are rough indicators of the aggregate morphology that surfactants will form in aqueous solution. The complex solution behavior of DSDMAC in water, including its strong tendency to form complex LC phases, e.g. lamellar bilayers and vesicles,^{5, 7} is readily rationalized in terms of this concept.

Overall, DSDMAC is routinely employed as a cationic emulsifier in cosmetic formulations. It typically is formulated with fatty alcohols to yield o/w emulsions with lamellar LC structures for improved stability, aesthetics, moisturization and active delivery. Due to its cationic nature, DSDMAC is highly substantive to hair and skin, thus it is frequently used for hair and skin conditioning. For hair care, DSDMAC is employed as an anti-static agent and to improve the wet and dry combing properties of hair. It is generally formulated into rinse-out conditioners containing high levels of fatty alcohol, e.g. cetyl alcohol, although it has been added to shampoos as well.⁸ In skin care applications, emulsifier systems comprising DSDMAC and fatty alcohols can be used to prepare lotions and creams to deliver “heavy” emollients such as petrolatum without the feeling of greasy residue.⁹