BEHAVIOR OF SILICONE SURFACTANTS 91 • ABILV•.0g 15"C • ABILWE0g 40"C .,F'•-• ABILWE 0g i ! ! ! i 0 1 2 3 4 5 6 i i ! i 14- n 12- o [----I DC Q2-5200 15"C , i i i i i i i 0 1 2 3 4 5 6 7 ! ! ! 9 10 Figure 1. A. Percent evaporation of Abil WE 90 during ten days at 15 ø, 40 ø, and 60øC. B. Percent evaporation of DC Q2-5200 during ten days at 15 ø, 40 ø, and 60øC. was 4% at 40øC, and 14% at 60øC. In DC Q2-5200, evaporation at 15øC was 8% at 40øC evaporation was 16%, and at 60øC it was 18%. These results may reflect differ- ences in the chemical composition of the two silicones. At 15 øC all three glycols increased in weight, the greatest increase occurring in glycerin, as a result of its greater hygroscopicity. At higher temperatures the glycols showed different behaviors. Evaporation was fastest in PG and was complete after 24 hours. However, PEG 400 and glycerin evaporated less readily. After 10 days at 60øC, evapo- ration in glycerin was 40% and evaporation of PEG was 15%. Silicone-glycol mixtures. We then tested mixtures of silicones and glycols. The latter can

92 JOURNAL OF COSMETIC SCIENCE modify evaporation and thus affect substantiveness, an important property of topical formulations. Samples of each glycol were prepared at concentrations of 25%, 40%, and 50% with each silicone. This step was made difficult by the difference in miscibility between the two types of compound, and by the high viscosity of DC Q2-5200. Samples were therefore treated ultrasonically for two hours before evaporation and freeze testing. The results showed that evaporation of all silicone-glycol mixtures changed with glycol content. Figures 2A and B, 3A and B, and 4A and B show the results for DC Q2-5200 70- -10 • ABIL WE 09 •"o• ABIL + 25% PG [77] ABIL + 40% PG •,)• ABIL + 60% PG 15øC - / I 60øC 10- D.C. Q2-5200 D.C. + 25% PG D.C. + 40% PG D.C. + 50% PG 15øC 40øC 60%3 Figure 2. A. Percent evaporation of Abil WE 90 with different concentrations of propylene glycol (PG) (25%, 40%, and 50%) during ten days at 15 ø, 40 ø, and 60øC. B. Percent evaporation of DC Q2-5200 with different concentrations of propylene glycol (PG) (25%, 40%, and 50%) during ten days at 15 ø, 40 ø, and 60øC.