98 JOURNAL OF COSMETIC SCIENCE , •2' 1' o Figure 1. Spreading in polyester at 24øC and 0.1% w. Initial []After $ min. E 1• • 1, . o •7 2111 Molecular Weight Figure 2. Foaming at 1% w. be the case, as shown in Figure 3. The stability of the oil-in-water emulsion increased with lowering of the DMC molecular weight. WETTING We evaluated the DMC compounds using the Draves Wetting Test. Results are shown in Figure 4. The data show that there is a strong relationship between molecular weight (and structure) and wetting for DMCs. The lower-molecular-weight materials have faster wetting times. This finding is a trend also observed for other surfactants where shorter or branched structures provide faster wetting (10,11). The smaller molecule allows for more efficient packing efficiency and dynamics. The materials with lower molecular

DIMETHICONE COPOLYOL 99 •Mineral Oil K]Si!lcone Oil (F350) Stability (5 = stable, 0 = not stable) 4' 3' 2' 1' 0 607 ß ! ß 1108 2111 Molecular Weight Figure 3. DMC emulsification ability (5% DMC/47.5% water/47.5% oil, mixed 5 rain at high shear). 60 50 ½ 40 "• 30 zo lO o 500 - - - 0.1%w 1.0%w _ ß mm .m mm .m mm .m ,, mm mm mm mm m mm ßmm mm• 1000 1500 2000 Molecular Weight Figure 4. Draves wetting ooe DMCs as a oeunction ooe molecular weight. 2500 weight were extremely effective at the higher concentration of 1.0% w. Their wetting speeds were almost instantaneous. The data, as shown in Figure 4, show that the slope of the curve does not change much until the molecular weight of the DMC reaches approximately more than 1200. The non-linearity of the graph of wetting time vs. molecular weight of the DMC predicts that molecules having a molecular weight between 600 and about 1200 should be effective wetting agents. This, coupled with other properties, such as irritation data, will allow for the selection of cost-effective materials that are both good wetting agents and, for example, possess low irritation potential (vide infra).