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

264 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS formation was investigated for a large number of detergents, the relative efficacy of most of these detergents in cleaning conditioner soil was not established. In this paper, it is shown that the light-scattering techniques described in reference 1 can be used to rapidly and conveniently answer the above questions concerning condi- tioner/detergent interactions on hair. As in reference 1 for shampoo complexes, it is shown, using light scattering, that conditioner:detergent complexes formed on the hair are very dulling and difficult to remove with common detergents. These effects are shown to be readily measured on single fibers, on hair tresses, and even on full heads of hair. Following this, surfactants not exhibiting formation of insoluble complexes on hair are presented, and the relative conditioner cleaning efficiencies of a large number of sur- factants is determined. The above measurements are performed with both conditioner actives and fully formu- lated conditioners. The results from both types of experiment are confirmed and sup- plemented with more detailed radiotracer experiments than were run in the previous work. The results in this paper show that light scattering can be used to rapidly and quanti- tatively measure the practical effects on hair of many hair care products. As was stated previously (1), much of this type of information would be difficult or impossible to obtain using other techniques. EXPERIMENTAL TRESS PREPARATION All tresses were prepared with three grams each of human hair purchased from DeMeo Brothers, New York. In order to minimize scattering from the interior of the hair, only virgin, Oriental hair was used (1). Permed tresses were prepared by perming 60-gram bundles of hair with a standard commercial perming product. After the initial perm, the hair was washed twice with a 20% solution of SODS, a detergent consisting of 45 % sodium octeth- 1 sulfate and 55 % sodium deceth-1 sulfate (Vista Chemical Co., Austin, TX). Following this treatment, the hair was permed and washed again, and then divided into three-gram tresses. TRESS TREATMENTS For all comparison series, a minimum of three tresses was prepared for each treatment. In addition, three control tresses, treated only with 20% SODS and representing "clean hair," were prepared for each series. When carrying out a comparison experiment, succeeding tresses in a series received different treatments so that any particular treat- ment was staggered throughout the entire series. For stearalkonium chloride (SAC)/detergent experiments, tresses were subjected to two prewashes, followed by three treatment cycles. In commercial conditioner/detergent experiments, the number of treatments was increased to five.