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j. Soc. Cosmet. Chem., 44, 263-278 (September/October 1993) Interactions of cationic and anionic surfactants on hair surfaces: Light-scattering and radiotracer studies CHARLES REICH and CLARENCE R. ROBBINS, Colgate-Palmolive Research Center, 909 River Road, Piscataway, NJ 08854-1343. Received March 10, 1993. Synopsis Light-scattering techniques, supplemented by radiotracer studies, have been used in this work to demon- strate formation on hair surfaces of insoluble complexes between some common cationic conditioner actives and anionic lauryl and laureth sulfates. These complexes, which were found to be very dulling and resistant to cleaning by C 12-based detergents, were shown to form in tress treatments and also in treatments of full heads of hair. Alkyl ether sulfates having hydrophobic chain lengths of 6, 8, or 10 were found not to form the above types of complexes on hair and were shown to be superior for use in cleaning conditioners. In experiments with conditioner actives, contributions to buildup were found from both conditioner and detergent deposition. In the case of commercial conditioners, buildup was observed only as a result of excess detergent deposition in the presence of conditioner. In both cases, formation of insoluble complexes led to greatly reduced cleaning by lauryl or laureth sulfate-based shampoos. INTRODUCTION In a previous paper, Reich and Robbins (1) described the use of light-scattering tech- niques to follow cleaning and soiling of the hair surface. Using the demonstrated techniques, along with dye staining methods, it was shown that complexes could form on hair between Polyquaternium-10 cations and myristate anions when these two species were deposited on the hair from different shampoos. Formation of these complexes was shown to have a negative effect since the resultant deposits were very dulling and quite resistant to removal from the fiber surface. In work previous to the above, Robbins et al. (2) demonstrated the formation of a different type of complex on hair, between cationic stearalkonium chloride (SAC) or cetrimonium chloride (CTAC) particles and conventional, anionic shampoo detergents. The former two species are conditioner actives commonly found in many commercial conditioners. Because of the nature of the techniques used in reference 2 to establish complex forma- tion, dye staining and radiotracers, it was not possible to say much concerning the effects on hair of complex formation. In addition, although the possibility of complex 263