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-

STAINING CATIONICS ON KERATIN 213 S•CI C-10-2 SAC & C. ALC. C-10-2 S XC/SI, S SAC & C. ALC. SLS -- SAC CREME RINSE SAC CREME RINSE C - 10 - 2 SLS SAC Figure 6. Treatment of wool swatches with a simple cationic vs. formulated conditioners and washing these with deceth vs. lauryl sulfate and staining with Red-80. Table II Radiotracer Analysis Showing Quantities of Anionic and Cationic Moieties Bound to Keratin After Treatment With a Conditioner Product # and Washing With Anionic Detergents mg Ionic moiety/gm Dry keratin Treatment Anion Cation Total bound Conditioner/ALS 4.0* 1.7 5.7* Conditioner/SDES 2.0 1.9 3.9 # Keratin contained 4.5 mg SAC/gm dry keratin after conditioner treatment, prior to washing. * Significantly different from corresponding value at or beyond the 95% level.