After choosing PEG-400 as a polyol, the experiments on PLO gel formulations at differ- ent ratios of each composition were performed using RSM. Stability was displayed in all formulations at room temperature (25°C) and constant temperature (45°C), but the for- mulated gels #2–6 and #2–11 showed separation and fl owability at low temperature (4°C) from day 7, which indicated a gradual phase separation with time. Complete phase separation occurred 3 weeks after starting observation of time-elapsed change. All other formulations showed stability even after 6 months (Figure 5). In the cycling test, com- plete phase separation occurred in #2–6 in the fi rst cycle and #2–11 in the second cycle. Excluding these two formulated gels, phase separation did not occur in all PLO gel for- mulations. Formulation #2–6 appeared to be unstable due to relative smaller amounts of poloxamer 407 and hydrogenated lecithin. Formulation #2–11 seemed to be unstable due to relatively smaller concentrations of poloxamer 407 and PEG-400. Of all testing formulations #2–3, #2–5, #2–6, and #2–11 with a poloxamer 407 concentration of 15.0%, phase separation occurred in #2–6 and #2–11. This outcome is thought to be at- tributable to relatively smaller amounts of PEG-400 and hydrogenated lecithin. Of all testing formulations #2–2, #2–6, #2–10, and #2–16 with a hydrogenated lecithin con- centration of 1.0%, phase separation occurred in #2–6 alone. This outcome seems to be resulting from relatively smaller content of poloxamer 407 at 15.0%. Of #2–4 and #2–11 with PEG-400 concentration of 15.0%, phase separation only occurred in #2–11. This outcome is thought to be attributable to relatively smaller amounts of poloxamer 407 and hydrogenated lecithin. The outcomes of stability evaluation revealed that all three phases of PLO gel had signifi cant effects on stability. MO RPHOLOGY OF PLO GEL Fo r observation of PLO gel morphology, FE-SEM was used to examine the morphology of stable PLO gel #2–3. After pretreatment with cryo-system, the structure of PLO gel Figure 5. After 3 weeks’ stability at low temperature (4°C) (PLO gel #2). JOURNAL OF COSMETIC SCIENCE 334

#2–3 resembled a microemulsion-based gel (10,30) and polymeric bicontinuous micro- emulsion structure (31) (Figure 6). A bicontinuous microemulsion structure is formed by mixing the appropriate amounts of oil, water, and amphipathic substances, and bicon- tinuous microemulsion is known to form an interesting structure consisting of undula- tion and boundary having a mean curvature (32). DS C MEASUREMENT Th e infl ection points of the DSC curves of the formulated PLO gel commonly lingered around –10°C, which corresponds to the temperature where property changes in PLO gel began to occur (Figure 7). Pha se separation or reduced viscosity (fl owability) occurred at low temperature (4°C) in the formulated PLO gel #2–5, #2–6, and #2–11, with DSC values of less than 0.4 around the peak of –10°C as shown in Figure 7, and this resulted in pre-marked marks on the surface disappear. On th e contrary, PLO gel formulations with DSC values of greater than 0.4 at –10°C were mostly stable. These results indicate that there is a correlation between formulation stability and DSC value. RHEOLO GY STUDY RESULT Rheolo gical characteristics were assessed using a rheometer. This instrument uses DWS, which is an optical technique derived from DLS. Because a rheometer determines rheo- logical properties based on the Brownian motion, this instrument has the advantage of accurately identifying formulation properties compared with physical appraisal methods. With rheology measurement, particle motion speed represents viscosity and particle dis- placement denotes elasticity. To pre sent them into numerical values, index values were obtained through data process- ing of the change in MSD with time. Macro viscosity index (MVI) indicates viscosity. Figure 6. Cryo FE-SEM result of PLO gel #2–3. PREPARATION AND EVALUATION OF PLURONIC LECITHIN ORGANOGELS 335