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

SENSITIVE PROBE OF HAIR SURFACE 231 SHAMPOO B1 SHAMPOO B1/ SHAMPOO C1 Figure 7. A dye-staining experiment testing the effects of washing with shampoos B1 and C1. The pink color of the swatch on the left indicates the presence of Polyquaternium-10 after washing with shampoo B 1. The absence of a pink color for the swatch on the right indicates the lack ofcationic binding sites as a result of complexation of Polyquaternium-10 from B 1 and myristate anion from C 1. order to obtain meaningful instrumental shine values, therefore, it is necessary to treat tresses, rather than single hairs, and to then measure the shine values for a number of hairs from each tress and average the results. Aside from the resultant quantitative data, there are two other advantages to treating tresses rather than single fibers. First, unlike the case with individual hairs, the shine of treated tresses can be subjectively assessed and, if desired, compared to instrumental data. In addition, the conditions employed in treating tresses are much closer to actual in-shower conditions than is true for single-fiber tests. In the latter case, even though a hair is exposed to only one to three drops of treatment solution, this is still more exposure than it would receive buried in a head of hair. Thus, although results from single-fiber tests are valid for the conditions employed, they would not necessarily be observed in normal usage. To confirm whether an observed effect on single hairs would actually occur under in-shower conditions, it is necessary to treat tresses (containing more than a thousand hairs) rather than single fibers.