SENSITIVE PROBE OF HAIR SURFACE 229 SHAMPOO C I (#2) SHAMPOO C I (#3) I I I 30 4õ 60 SCATTERING ANGLE Figure 5. A single-fiber shampoo C1 experiment. the dulling B 1 residue was removed from the hair. These experiments demonstrate that light scattering can be used to follow both deposition (soiling) and removal of particles (cleaning) from the hair surface. Figure 5 shows another single-fiber experiment using shampoo C 1, a commercial prod- uct that at the time of sale contained sodium myristate, a component of soap that is well known to deposit on and dull hair (11). As with the B1 experiments, successive treatments with shampoo C1 caused dulling, in this case a result, probably, of depo- sition of sodium myristate particles on the hair. Again, as with the preceding experi- ment, after treatment of the dulled hair with 20% SLS, the original, clean hair curve was recovered. Figure 6 shows the results of a single-fiber experiment in which a clean hair was treated twice with shampoo B 1, resulting in dulling from shampoo residue. An attempt was made to clean this residue with shampoo C 1, with the expectation that initially the C 1 would remove accumulated B1 residue and that further applications would lead to accumulation of new C1 deposits. Surprisingly, application of shampoo C 1 did not lead to an initial increase in shine but, unexpectedly, to a great increase in dullness, much larger than the sum of the individual shampoo effects. This implies that the deposits from the two shampoos are interacting to form a new residue that is more dulling to the hair than the former deposits. That a new type of residue has formed is also supported by the observation that attempting to reverse the increased dullness by washing with SLS did not lead to a change in the

230 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS CLEAN HAIR POO (#2) POO CI I• 30 45 60 SCATTERING ANGLE Figure 6. A single-fiber experiment measuring the effect of washing with two different shampoos. Note the huge increase in diffuse scattering and the great decrease in shine after treating the hair with shampoo C1. light-scattering curve, indicating that, unlike the individual residues, the combination residue is resistant to removal by SLS. Formation of a B I:C 1 complex, presumably between the Polyquaternium-10 cation and the myristate anion, was further tested by performing a dye-staining test, the results of which are shown in Figure 7. The wool swatch on the left in this figure was washed with shampoo B1 and exhibits a pink color as a result of subsequent treatment with Sirius Red. This dye binds to wool only in the presence of bound cationic (12) the color, therefore, indicates that some Polyquaternium-10 was deposited on the wool surface from shampoo B 1. The swatch on the right in Figure 7 was washed with shampoo B 1, then shampoo C1, and then treated with Sirius Red. In this case, the swatch retained almost no red dye, indicating that after treatment with C 1, very few cationic binding sites were left on the swatch. Since, from the single-fiber experiments, it is known that Polyquaternium-10 still remains on the surface, one must conclude that it is no longer available for binding to Sirius Red as a result of complexation with myristate anion. The conclusion from light scattering that a complex was formed on the hair surface is thus confirmed. TRESS TREATMENT EXPERIMENTS As stated previously, single-fiber results, such as those in the preceding section, cannot be treated quantitatively because of the tremendous variation among single hairs. In