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.

BEHAVIOR OF SILICONE SURFACTANTS 93 A 70- LU • ABIL WE 09 ?• ABIL + 25% PEG • ABIL + 40% PEG :,• ABIL + 60% PEG 15øC 40øC 60øC -lO • DC Q2-5200 • DC +25% PEG P•-• DC + 4.0% PEG t,'• DC + 50% PEG 15øC 40øC Figure 3. A. Percent evaporation of Abil WE 90 with different concentrations of polyethylene glycol (PEG) (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 polyethylene glycol (PEG) (25%, 40%, and 50%) during ten days at 15 ø , 40 ø , and 60øC. and Abil WE 09 in combination with each glycol and at each temperature. Behavior of the mixtures varied depending on the temperature. At 15øC all glycols showed similar behavior. As glycol concentration increased, evaporation decreased. This was not sur- prising in view of the ability of individual glycols (particularly glycerin) to absorb water and increase in weight at 15øC. At 40 ø and 60øC, the evaporation generally decreased as the concentration of PEG 400 and glycerine increased. After 10 days at 40øC, evaporation of mixtures containing