134 JOURNAL OF COSMETIC SCIENCE Since the x-ray energy penetrates only a few microns into the hair tress, it only measures the silicone oils that have deposited onto the surface of the hair tress, i.e., onto the hair cuticle. Because we do not know the absolute value for the amount of silicone deposited onto the hair [although methods exist to measure these absolute amounts (9,10)], we are looking instead at qualitative values of silicone deposition that are taken as counts/ second. Therefore, only tresses washed using carefully controlled model shampoo for- mulations treated under similar washing conditions on the same type of hair can be evaluated, and the use of specific control tresses is critical for relating data. RESULTS AND DISCUSSION In our original discussion, we noted a surprising result that we show graphically in Figure 2. When virgin brown tresses (DeMeo Brothers) are washed with a model shampoo that contains a silicone emulsion but does not contain a cationic polymer (Formulation E), the silicone not only deposits, but after multiple washings continues to deposit, showing indications of a build-up phenomena. The control tresses in this case are also shown and include tresses washed one time with a non-ionic surfactant, 15- Pareth-9 (Formulation G) and tresses washed one and ten times with our model shampoo base without silicone or cationic polymer (Formulation F). However, when we examined the data for our formulation containing a low-molecular-weight polyquaternium-10 at 0.5 wt%, (Formulation A), we noted that while initial single-wash silicone deposition was slightly depressed compared to the silicone-only shampoo, after multiple washes the presence of the cationic polymer appears to modulate the silicone deposition and the build-up phenomena is suppressed. This suggests to us that in the washing process, the two polymers must interact with one another in some fashion that is not presently understood due to the complexity of the application process, which includes high shear, foaming, and dilution effects. While the influence of the cationic polymer on the silicone oil deposition is readily apparent from Formulation and Wash Number Figure 2. Relative silicon x-ray fluorescent intensities for hair tresses treated with various shampoo for- mulations including data for single (lx) and multiple (10x) washing experiments (except as noted).

SILICONE OIL DEPOSITION ON HAIR 135 these experiments, the juxtaposed influence of the silicone oil on the cationic polymer deposition is not, and this aspect is currently a topic of investigation in our laboratories. The effect of cationic polymer molecular weight can also be seen from the data in Figure 2. It appears that as the molecular weight of the cationic polymer increases (compare Formulation A with Formulation D), the amount of silicone oil that deposits on the hair increases as well. We note that in a single washing experiment, the higher-molecular- weight polyquaternium-10 polymer deposits nearly 60% more silicone than the com- parable lower-molecular-weight polymer of equal charge. This further suggests to us that perhaps factors such as the rheology of the shampoo during application and rinsing, or the hydrodynamic volume of the cationic polymer, can also play an important role in modulating the oil deposition. Looking at the effect of cationic polymer concentration, we note that for the medium- molecular-weight cationic polymer (Polymer 1) there is little change in the amount of silicone depositing on the hair even after repeated washings down to a concentration of 0.3 wt% (compare Formulations A and B) (Figure 3). However, when the cationic polymer concentration drops to O. 1% (Formulation C), the effect on silicone oil depo- sition is quite dramatic and the shampoo behaves more like a formulation that does not contain cationic polymer, i.e., the silicone build-up phenomena is noted again. It appears that when the cationic polymer concentration falls below a certain level, its ability to interact with the silicone emulsion and influence the silicone deposition diminishes. We were curious as to whether or not our analysis technique was providing results that might have significance to the behavior of commercial shampoos. For this reason, we elected to examine a commercial shampoo that we knew to contain a surfactant platform similar to our own model platform containing polyquaternium-10. However, we do not ,',' 15.0 • 10.0 • 5.0 0.0 Figure 3. Effect of oationic polymer concentration (0.5, 0.3, and 0.1 wt%) on relative silicon XRF intensities for hair tresses treated with cationic Polymer 1 and data for a commercially available "2-in-l" shampoo containing dimethicone and polyquaternium-10 (1 and 10 washes).