POLY(GLYCERYL) ALKYL ETHER SURFACTANTS 425 IOO 80 o 60 • 4o E i- 2O 0 0 Water I I ! I )c ic c [c o o W ! L• ! El I I I 0.2 0.4 0.6 0.8 1.0 0.2 wt. fraction RmTs.7G6.• Water //Ii , 0.4 0.6 wt. fraction i lb) LC• .o RmEO8 0.8 Figure 6. Phase diagrams of(a) R•2T5.vG6.•/H20 and (b) R•2EOs/H20 (17,18) systems. Table I Surface Properties of Aqueous Solutions of R12T 3 2G4.0 and R12EO 6 R12T3.2G4.0 R•2EO6 HLB value 17.7 11.7 c Cloud point a (øC) 57.0 52 a cmc s (mol/1) 1.9 x 10 -5 8.7 x 10 -Se • 1 wt% solution bat 25øC Creference 21 (HLB-v = E/5) areference 22 ereference 23. EMULSIFYING ABILITY Fine emulsions are produced by the combination of poly(oxyethylene) and lipophilic surfactants close to the required HLB-value of the emulsion system. Therefore, the emulsifying ability of poly(oxyethylene) surfactants decreases with an increase in the oxyethylene chain length (25). The emulsifying ability of these surfactants was com- pared with R12EO25 (HLB-v = 20) and R12T7.8G7. 9 (HLB-v = 30) from the mean particle size of the O/W emulsions. The emulsions were prepared by employing sor- bitan monostearate as the lipophilic surfactant. Figure 8 shows the relationship between the mean particle size and the weight fraction of hydrophilic and lipophilic surfactants. R12T7.8G7. 9 produced a smaller emulsion particle than R12EO25. Even though the HLB- value of R12T7.867.9 is higher than that of R•2EO25, it produces fine O/W emulsions. This result shows that R•2TxGy has a greater emulsifying ability than R12EO x. Five types of oil were emulsified by the paste emulsification method (similar to the English method) (26). The emulsification was performed as follows: The same weights of R•8T•4 ' •G•3.2 and water were mixed. An oil phase was added to the surfactant contin- uous solution with stirring. A gel emulsion was formed when the addition was finished. Then a water phase was added to the gel with stirring. Since a low interfacial tension is given between oil and surfactant phases (27), a fine emulsion is formed in this system. The mean particle size and the composition of the O/W emulsions are shown in Table

426 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS / R'2 3yTG, / 20 / JR,aTxG• • /0' /J2"' Ri83yTG. y i io I I I I I 0 2 4 6 8 I0 Glyceryl chain length (¾] Figure 7. HLB values of R.TxGy ! i RmEOx I I 0 I0 20 30 Oxyethylene chain lengfh (x] and R.EOx determined by phase inversion emulsification (14). II. R,TxGy is suitable for emulsification because it does not provide hard liquid crystals with water. Hard liquid crystals, hexagonal or cubic liquid crystals, that appear in POE-type surfactant systems interrupt the dispersion of oil droplets in the surfactant continuous phase. If these liquid crystals are eliminated by additives, POE-type surfac- tants can also produce fine O/W emulsions (28). R18T14.1G13.2 emulsified several types of oil to less than 1-•m particles. All the emulsions were stable and did not coalescence for three months at 20øC. PHASE DIAGRAMS OF THE TERNARY NONIONIC SURFACTANT/OIL/WATER SYSTEMS To understand why the HLB-values of the R]2TxGy system are high, a phase diagram of a pseudo three-component system of (R12TxGy + liquid paraffin)/(sorbitan monooleate + liquid paraffin)/water was constructed (Figure 9a). In the phase inversion emulsifica- tion, the water is added to the mixture of the oil and surfactant. Point S in Figure 9a is the starting point of emulsification. When water was added to the solution, the solu- tion became clear (I•)) and then blue translucent. This blue translucent microemulsion exhibited optical anisotropy under polarized light (LC=). When the weight ratio of sorbitan monooleate/R12T7.8G7. 9 is 7:3, the microemulsion region gives a peak of max- imum water solubilization. When water is added to this microemulsion, a fine O/W emulsion is formed. A W/O emulsion was formed in the R]2EO2o/sorbitan monooleate system when water was added at the maximum solubilization point (Figure 9b). The volume of solubilized water in the R•2T7.8G7. 9 system was about 1.5 times that of the R•2EO2o system. The higher water solubility and the wide lameliar liquid crystalline region of the R•2TxGy systems suggest that the aggregation number of R•2TxGy is larger than that of R]2EO x. It has been reported that the maximum solubilization of water in POE nonionic surfactant systems appeared above the three-phase temperature range (29,30). Therefore, a W/O emulsion forms in this system. In the system of R•2T7.8G7.9, the solubilization of water increased rapidly as the concentration of the surfactant increased, and a lameliar liquid crystalline phase was formed (Figure 10). When the surfactant concentration decreased, the oil phase separated from the liquid