JOURNAL OF COSMETIC SCIENCE 416 Turb idity meter. The O /W emulsions stored at room temperature for 1 week were used in this experiment. The turbidity measured by the turbidity meter (Lutron) (Figures 10 and 11) showed a similar tendency to that measured by the UV-vis spectrophotome- ter (Figure 6). The maximum turbidities of liquid paraffi n, CUFO, CUPO, HF, and CJSO emulsions were measured at HLB values of 10.42, 14.90, 14.90, 7.06, and 5.94, respectively. Drop let size analysis. The turbidity value in Figure 10 showed the maximum value in the HLB value of the average minimum droplet size (1,2). The lowest mean droplet size of liquid paraffin (137.77 nm ± 1.46 nm), CUFO (138.00 nm ± 1.73 nm), CUPO (123.50 nm ± 3.31 nm), and CJSO (150.60 nm ± 2.88 nm) emulsions were obtained at HLB values of 14.90, 14.90, and 5.94, respectively (Figures 12 and 13). In the m ethod of Orafi diya and Oladimeji (1) required HLB of liquid paraffi n was about 12, but it was 10.42 in this study by the analysis of mean droplet size and turbidity. This is seen as a difference in the molecular weight and structure of liquid paraffi n. Meher et al. (26) reported that required HLB of light liquid paraffi n was 11.80, but Niczinger et al. (2) reported required HLB of liquid paraffi n as 10.0. Figure 4. Appearance after 1 week storage of HF emulsions. Figure 3. Appearance after 1 week storage of CUPO emulsions.

DETERMINATION OF REQUIRED HLB VALUE 417 In the c ase of CUFO and CUPO, required HLB was tested as 14.9 in this study, but several previous studies reported that required HLB of D-limonene, the main com- ponent in lemon oil, was 12.0 (2,27). However, depending on the geometrical struc- ture of surfactants used in emulsion production, there are cases in which the required HLB for D-limonene was 13.7 (28) and 15.0 (29). In addition, according to Lu et al. (30), the nanoemulsion containing 10% D-limonene showed a minimum particle size and the maximum encapsulation rate when the HLB value was 12, but it is con- sidered that this experiment needs to be expanded beyond HLB 12. The lowe st mean droplet size of HF emulsion (153.97 nm ± 4.23 nm) was obtained at an HLB value of 7.06 (Figure 14). From the turbidity experiment, the CUFO and CUPO emulsions had the minimum droplet size at the highest HLB value of 14.90. Therefore, the CUFO and CUPO needed additional experiments with polysorbate 20 (HLB = 16.70) to have the HLB value higher than 14.90. Figure 5. Appearance after 1 week storage of CJSO emulsions. Figure 6. Turbidity of liquid paraffi n emulsions in the HLB range from 3.70 to 14.90, which were measured by a UV-vis spectrophotometer after 1 week storage at room temperature (n = 3 ±SD).