228 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS z uJ I-- z LEAN HAIR SHAMPOO BI (#1) SHAMPOO B I (#2) SHAMPOO B I (#3} SHAMPOO B I (#4) SLS 15 30 45 60 SCATTERING ANGLE Figure 4. A single-fiber experiment testing the effect on hair of shampoo B 1. The hair was washed with SLS at the beginning of the experiment (clean hair) and at the end. The same curve was obtained in both cases. quantitative results from a single hair to be meaningful. A particular result must therefore be repeated several times on different hairs in order to be considered real. Bearing this in mind, and also the fact that single-fiber treatment conditions are very different from tress and in-shower treatments, one can use single-fiber screening tests as a convenient means of determining the possible effects of many different products on hair. This method is especially useful when hairs are undergoing a series of treatments, since after each particular step in the series, a light-scattering scan can be run in order to determine the effect of that particular step. This can be very helpful in elucidating the mechanism of a particular effect. Figure 4 shows the results of a series of treatments of an Oriental hair with shampoo B 1. This is a commercial product that, at the time these experiments were performed, contained Polyquaternium-10, a polycationic well known to be substantive to hair, in a trideceth-7 carboxylic acid detergent system. The hair was first washed with 20% sodium lauryl sulfate (SLS). The resultant light- scattering curve is considered that of a clean hair. Following this, successive treatments with shampoo B 1 (followed by water rinses) caused dulling, indicated by decreases in the peak height along with increases in diffuse scattering. This loss of shine was caused by deposition of shampoo residue, probably Polyquaternium-10, on the hair surface. After four treatments with B 1, the hair was again treated with 20% SLS. The resulting light-scattering curve was congruent with the original, clean hair curve, implying that

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