STAINING CATIONICS ON KERATIN 211 CTAC CTAC/CoI0 CTAC/C-12 CTAC/C-14 CTAC/C-16 AOS SURFACTANTS Figure 4. Wool swatches stained with Red-80 dye after treatment w•th CTAC and washing with AOS detergents. just cationic and fatty alcohol compare favorably to either pure SAC or CTAC in the modified dye-staining procedure. Figure 6 compares swatches treated with SAC, a partially formulated conditioner con- taining SAC and cetyl alcohol, and a commercial conditioner based on SAC and ceteth- 2 after washing with both sodium deceth-2 sulfate and SLS. All swatches washed with the deceth-2 sulfate show a light stain, in contrast to those washed with SLS, which do not stain. This suggests that the cationic adsorption, binding, and washing from ker- atin is similar whether it is used pure in solution or formulated into a conditioner. Nevertheless, we decided to test this hypothesis by radiotracer experiments. Table IT summarizes the results of an experiment in which a formulated conditioner containing radiolabeled SAC and ceteth-2 was washed from wool fabric by solutions of radiolabeled SDES and ALS. The binding of the anionic detergent is similar to the case where pure cationics are washed (compare the results of Tables T and TT). Here roughly two times the amount of ALSvs SDES binds to the keratin-containing cationic. Fur- thermore, in the dye-staining test, the SDES species can be displaced by the anionic dye, but the lauryl sulfate moiety cannot. In contrast to the case of washing pure cationic from keratin, these results with a fully formulated product show that both of these anionic detergents, ALS and SDES, remove a similar amount of cationic from the swatch, but a large difference exists in the amount of anion that is left behind, with nearly two times the amount of lauryl sulfate vs deceth sulfate being left behind on the keratin. From all of these staining and radiotracer results, we conclude the following: Swatches of keratin fibers when treated with cationic detergents bind those detergents by electro- static and Van der Waals attractive forces. When one attempts to remove the cationic detergent from the hair by washing with an anionic detergent, an electrostatic interac-

212 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS CTAC CTAC & C. ALC. SAC SAC & C. AI,C. EFFECT OF LIPID Figure 5. The effect of lipid on the dye-staining properties of cationic surfactants on keratin substrates. tion occurs between detergents. If the water solubility of this interaction product is in the vicinity of or greater than that of the decyl sulfate-cetrimonium species, much of the cation is removed from the swatch, but staining can still occur because the anionic dye can displace the more water-soluble anionics like octyl or decyl sulfate (see Ap- pendix for a complete list of the surfactants and staining results). However, if the water solubility of this interaction product is less than that of the dodecyl sulfate-cetri- monium species, then staining does not occur because the anionic dye cannot displace the anion from the anionic-cationic complex species. Buildup on hair occurs because the anionic moiety of the washing detergent binds to the hair with the cationic species, and in the case of fully formulated systems, the ratio of binding anion/cation may be much greater than 1. We confirmed these conclusions by means of light-scattering experiments and subjective comparisons in actual half head tests that demonstrate that shinier, cleaner hair results from washing hair containing cationics with SDES vs. ALS. Therefore, this mechanism forms one basis for the phe-