SUMMER 2014 • Vol. 20 No.6
New York Society of Cosmetic Chemists
www.nyscc.org
The Use of Anionic/Cationic Surfactant Complexes to Create Special Effects in Cosmetic Formulations …Paul Thau
O
ver twenty years ago, during a visit to a local pharmacy, I decided to evaluate a tester unit of the recently introduced Norwegian Daily Treatment Lotion for Dry Skin by Neutrogena. I was immediately impressed by the smooth, soft texture imparted to the skin by this product. The skin feel was very distinctive, somewhat similar to that imparted by a classic cationic emulsion system. A review of the ingredient labeling on this product, shown below, revealed an unusual composition—a cationic emulsifier in an anionic soap formulation: Water, Glycerin, Caprylic/Capric Triglyceride, Dimethicone, Octyldodecanol, Petrolatum, Cetyl Alcohol, Glyceryl Laurate, Stearic Acid, Stearyl Alcohol, Hydrogenated Lanolin, Triethanolamine, Fragrance, Dimethicone Copolyol, Methylparaben, Imidazolidinyl Urea, Steapyrium Chloride, Sodium Cetearyl Sulfate, Propylparaben, BHA, BHT, Sodium Sulfate.
One would not ordinarily expect to find a cationic ingredient such as Steapyrium Chloride included in a typical soap based, Triethanolamine Stearate, emulsion. That is because it was commonly thought, and taught, that cationic and anionic surfactants should not be combined because of the risk of incompatibility, including precipitation or instability. However, I did observe the listing of Sodium Cetearyl Sulfate immediately after Steapyrium Chloride on the ingredient labeling. Based upon my awareness that anionic/cationic polymers had been used effectively in the formulation of hair mousse foams, I decided to conduct a simple experiment. Equivalent molecular weights of Steapyrium Chloride (0.25%) and Sodium Cetearyl Sulfate (0.185%) were combined in deionized water. It was found that in spite of the interaction between these two oppositely charged surfactants, a clear, water-soluble complex at the concentrations listed above was produced. Procedure: Each surfactant was dissolved in water and heated to 70 ºC. The two solutions were then combined. After cooling to room temperature, no precipitation was evident. The pH of the resultant solution was 6.6. A prototype Triethanolamine Stearate skin treatment emulsion was prepared with the inclusion of the above anionic/cationic surfactant complex at a concentration of less that 0.50%. The skin feel aesthetics of this prototype emulsion did closely match that of the reference Neutrogena product. An interesting finding: Neutrogena continues to use the identified cationic/anionic complex in their currently marketed product, (Continued on page 6)
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