STATISTICAL ANALYSIS Ex periments were repeat ed three times, and data were presented as means ± SD. Signifi - cance in difference was tested by Student’s t-test. Differences were considered signifi cant at * p 0.05, ** p 0.01, and *** p 0.001. RESULTS AND DISCUSSION S TABILITY EVALUATION Sta bility evaluation was conducted at low temperature (4°C), room temperature (25°C), and constant temperature (45°C) each. PLO gel remained the same and stable at room (25°C) and constant (45°C) temperatures, but separated and turned to liquid at low tem- perature (4°C), showing that the gels were not suitable ingredients for cosmetic formula- tions. In the polyol selection experi ment, stability evaluation by temperature revealed that the all-formulated organogels were stable at room (25°C) and constant (45°C) temperatures. Excluding PEG-400, phase separation began to occur from day 7 at low temperature (4°C), and complete separation occurred 3 weeks after starting observation of time- elapsed change (Figure 4). Based on these fi ndings, PEG-400 was considered as the most appropriate PLO gel, and the experiment was additionally carried out by choosing PEG- 400 as a polyol. In the cycling test, phase separation also occurred in all PLO gel, except for PEG-400 (data not shown). When PEG (polyethylene glycol) is adsorbed to the colloidal surface, the colloidal activi- ties are substantially reduced, and the growth rate of the colloids is limited in certain aspects. In the experiment, the addition of PEG changes the kinetics of the growth pro- cess by inducing the rapid growth of nucleation and the aggregation of nanoparticles. Therefore, the addition of PEG can promote the crystallinity of samples and change the product morphology (29). The present study confi rmed that the addition of PEG-400 maintains the stability of PLO gel at low temperature. Figure 4. After 3 weeks’ stability at low temperature (4°C) (PLO gel #1). PREPARATION AND EVALUATION OF PLURONIC LECITHIN ORGANOGELS 333

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