in .s , · ·s: .s en en U) ANTI-AGING EFFECTIVENESS OF RETINOL EMULSIONS 273 80000 70000 60000 • at opening 50000 - • - after 1 day 40000 - - • - ·after 3 days 30000 - ..f- - after 7 days 20000 - -:a - after 10 days 10000 0 a 5 10 15 Fi gu re 11. Viscosity of RETI C concentrate emulsion before and after storage at 25 ° C. 185000 165000 145000 125000 105000 85000 65000 45000 25000 5000 D 5 10 15 20 25 shear rate (s- 1 ) -◄•-- upper curve at opening - - - • - - back curve at opening .a. upper curve after 1 day - - - A- - - back curve after 1 day )I( upper curve after 3 days - - - x- - - back curve after 3 days --i---upper curve after 7 days - - - +- - - back curve after 7 days o upper curve after 10 days - - - o- - - back curve after 10 days Figure 12. Flux rheograms of RETI C emulsion after storage at 25 ° C. OPTICAL MICROSCOPE ANALYSIS Microphotographs of RETI C and RETI C concentrate emulsions are presented in Figures 14 and 15, respectively. In both cases, the emulsions at opening (Figures 14a and 15a) show the typical structure ofW/O/W multiple systems. However, in the emulsions after storage at 40 ° C for ten days (Figures 146 and 156), this multiple structure disappears and the droplets are enlarged and aggregated, proving a certain instability of the two systems.

274 .§. tn 185000 165000 145000 125000 105000 85000 65000 45000 25000 5000 a 5 JOURNAL OF COSMETIC SCIENCE 10 15 20 shear rate (s- 1 ) 25 _..,__ upper curve at opening - - ♦ - · back curve at opening --+--upper curve after 1 day - - •- - · back curve after 1 day -upper curve after 3 days - - •- - · back CU1Ve after 3 days --+--upper cL1Ve after 7 days - - + - · back curve after 7 days ---e--upper curve after 1 O days - - 0- - · back CLD'Ve after 1 0 days Figure 13. Flux rheograms of RETI C concentrate emulsion after storage at 25°C. Table II Conductivity of RETI C and RETI C Concentrate Emulsions After Storage at 25°C Days of storage RETI C RETI C concentrate 1 1.06 mS 1.00 mS 3 0.96mS 0.55 mS 7 0.98 mS 0.51 mS 10 0.71 mS 0.46 mS (a) (b) Figure 14. Microphotographs (1250 x) of RETI C emulsion at opening (a) and after storage at 40 ° C for 10 days (b).