140 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS substantially with the deposition of a little amount of silicone. However, this improve- ment seemed to level off with increasing deposition. High-molecular-weight silicones (gums and the gum blend). The % ACL reductions of the three treatments (gums 1 & 2 and blend) were in the 25%-50% range for wet combing and in the 65%-85% range for dry combing. As seen in Figure 3 (A for gum 1, B for gum 2, and C for blend), there is an initial rapid increase in combing performance improvement (for both wet and dry combing) followed by a gradual leveling off with increasing silicone deposition on hair. The leveling off of the performance occurs with our lowest data point, which is around 200 •xg silicone/g hair. Thus the minimum amount of silicone required for the improved performance, as well as the threshold level at which the improvement levels off, is between 0-200 •xg silicone/g hair. Yahagi (15) has shown that the kinetic frictional coefficient qXk) of dry hair fibers was reduced when amounts greater than 100 •xg silicone/g hair were deposited on the fibers (using a polydimethylsiloxane of molecular weight of 220,000). This amount was explained as perhaps being the critical level that is needed to form a lubricating, thin film on the surface of the hair. These high-molecular-weight siloxanes (HMWS) thus improve wet and dry combing 100' 80- 40- 20- A 250 500 750 1000 1250 Amount Silicon Deposited (gg Si/g hair) 100 80- 40 - 20- I i I i 250 500 750 1000 1250 Amount Silicon Deposited (gg Si/g hair) 100 20- /• • c 0q i I I I 250 500 750 1000 1250 Amount Silicon Deposited (gg Si/g hair) • 60- c..) 40- Figure 3. Dry (¸) and wet (O) combing performance of gum 1 (A), gum 2 (B), and blend (C) in absence of the quat.

SILICONE-QUAT INTERACTIONS 141 performances, the dry combing improvement being noticeably superior to the wet combing effects (based on %ACL reduction). Low-molecular-weight silicones (fluids). The data points are a lot more scattered for mem- bers of this class, especially for fluid 1. As shown in Figure 4 (A for fluid 1, B for fluid 2, and C for fluid 3), there does not appear to be much of a difference between dry combing and wet combing improvement. The %ACL reductions of the three treatments were in the 35%-60% range for both wet and dry combing. The same trend (of improved performance for low amounts of silicone deposited followed by leveling off) is seen with these lower molecular weight polydimethylsiloxanes (LMWS). Our lowest data point (for fluids 2 and 3) in this case is around 55 •g silicone/g hair, so that the minimum amount of silicone required for the improved performance and the threshold level at which the improvement levels off is now between 0-55 •g silicone/g hair. Comparison between HMWS and LMWS. As Figure 5A shows, the HMWS display dry combing performance superior to that of the LMWS. This is in good correlation with a study where the •k value of dry hair fibers was measured as a function of the molecular weight (Mw) of the PDMS depositing on the hair (15). It was found that the coefficient decreased (i.e., improved lubricity) as the molecular weight of the silicone increased, provided that the Mw was greater than 20,000. e• 60 •- 40 100 100 - • , ,0 A ' o'o 0 250 500 750 1 0 1250 Amount Silicon Deposited (gg Si/g hair) 80- 60- 40- 20- o 0 250 o B 500 750 1 0 1250 Amount Silicon Deposited (gg Si/g hair) 100 • 60 0 •. 40 Ool I I i J0 0 250 500 750 1 0 1250 Amount Silicon Deposited (gg Si/g hair) Figure 4. Dry ( ¸ ) and wet (O) combing performance of fluid 1 (A), fluid 2 (B), and fluid 3 (C) in absence of the quat.