808 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 6o[ 1 30- / INOIL 0 20 40 60 80 100 ø1o TWEEN 80 IN AQUEOUS PHASE Figure 10. Effect of initial surfactant location on emulsion stability for oley] alcohol system prepared at slow mixing speed (170 rpm, 18-hour mixing, 15-min standing) 60 50 z o_4 o • 30 • 20 10 TWEEN 80 INITIALLY IN WATER , TWEEN 80 INITIALLY IN OIL 0 .... 0 20 40 60 80 100 % TWEEN 80 IN AQUEOUS PHASE Figure 11. Effect o• initial surfactant location on emulsion stability for oleic acid system prepared at slow mixing speed (170 rpm, 18-hour mixing, 15-min standing)

EMULSION STABILITY 809 6ø t o 3o • 20 lO o o ! I TWEEN _ IN OIL '-• O 80 INITIALLY TWEEN 80 I N I TI ALLY IN WATER • ) i r i I 20 40 60 8O 100 % TWEEN 80 IN AQUEOUS PHASE Figure 12. Effect of initial surfactant location on emulsion stability oeor octyldecy] triglyceride system prepared at slow •nixing speed (170 rpm, 18-hour mixing, 15-rain standing) combination at HLB 10 using the same procedure with varying initial surfac- rant location. The results given in terms of visually observed emulsion quality are presented in Table I. Emulsion O is the emulsion which was prepared by initially placing the Tween 80 in the oil phase and Emulsion W denotes the corresponding emulsion, with the same composition, prepared with the Tween 80 initially in the aqueous phase. The better emulsion here means a fi- ner particle size and, usually, better stability. Clearly, under a slow mixing speed, initial placement of Tween 80 in the oil phase produced more stable emulsions in all of the above oils tested.* It is of interest to note that this difference diminishes as the mixer speed used for emulsification was increased from 170 to 650 rpm as shown in the data pre- sented in Fig. 13. Under very slow mixing, the rate of emulsification was also relatively low. To study the reasons for the above difference, microphotographs were taken * The only exception to this statement was found in emulsions prepared with multi- sterol dispersed in mineral oil. This material is sold in the U.S.A. under the trade names of Amerchol L-101© and Ritachol©. Ilowever, since it is a complex mixture with sterols acting as low HLB surfactants, it is not too surprising that it acts differently from other oils. Moreover, it was found that raising of the total HLB by increasing the Tween 80 / Arlacel 80 ratio reduced the above difference.