In c onventional PLO gel formulations, isopropyl palmitate (298.5 g/mol) or isopropyl myristate (270.5 g/mol) was used to dissolve hydrogenated lecithin in the oil phase. In the present study, CEH (368.6 g/mol) with higher molecular weight was used. Vari ous polyols were tested in the preliminary experiment (Table I). Polyols are used as moisturizer because of their humectant function, and can serve as cosolvents of active substances and act as cosurfactants through hydrogen bonding with water molecules (25). Polyol candidates used in the experiment are all commonly used as cosmetic ingredients, including butylene glycol, dipropylene glycol, pentylene glycol, 1,2-hexanediol, and PEG-400, and tests were performed for each substance at a concentration of 18%. RANG ES OF THE INDEPENDENT VARIABLES IN RSM In t his study, RSM was used to design the experiments to determine the effects of hydro- genated lecithin, the main constituent of the oil phase PEG-400 of the polyol phase and poloxamer 407 of the water phase on PLO gel formulation by choosing PEG-400 as a representative polyol based on the results of preliminary experiments. The concentrations of hydrogenated lecithin, PEG-400, and poloxamer 407 were selected as independent variables. The range of independent variables is shown in Table II. For experiment design, Design-Expert Version 11 Software (Stat-Ease Inc., Minneapolis, MN) was used, and Box–Behnken design, an RSM design, was used in the experiment. The Box– Behnken design involves IBFact, center points, and factors located at the same distance from the center of the cube. Figure 3 represents the structure of the Box–Behnken design with three factors (26). Figure 3 and Table III depict a 17-run Box–Behnken design. Usin g the data collected from the experiment design, the relationship between response variables (Y) and independent variables (X) can be expressed as a mathematical formula, and this equation is called a model (14). In this study, a response surface model by RSM can be represented as the following equation. 2 2 0 1 2 3 12 13 23 11 22 33 = + + + + + + + + + i Y a a A a B a C a AB a AC a BC a A a B a C2, whe re Yi presents the estimated value of the response variable, and A, B, and C are inde- pendent variables. The value of a0 is a constant, and ai, aii, and aij are the linear, quadratic, and interactive coeffi cients, respectively. Table I Basic Formula for PLO Gel Preparation with Different Three-Phase Compositions Ingredients #1–1 #1–2 #1–3 #1–4 #1–5 Oil phase Hydrogenated lecithin 1.8 1.8 1.8 1.8 1.8 CEH 10.2 10.2 10.2 10.2 10.2 Polyol phase 1,2-Hexanediol 18.0 - - - - Butylene glycol - 18.0 - - - Dipropylene glycol - - 18.0 - - Pentylene glycol - - - 18.0 - PEG-400 - - - - 18.0 Water phase DI-water To 100 To 100 To 100 To 100 To 100 Poloxamer 407 20.0 20.0 20.0 20.0 20.0 Phenoxyethanol 0.3 0.3 0.3 0.3 0.3 PREPARATION AND EVALUATION OF PLURONIC LECITHIN ORGANOGELS 329

STABI LITY TEST This study performed the sensory evaluation of time-elapsed change made over a month by date in the formulated PLO gel stored at low temperature (4°C), room temperature (25°C), and constant temperature (40°C). To determine the fl owability and separation of formulations, the cycling test was conducted to test physical stability of formulations by storing them at –15°C, 40°C, and 25°C each for 24 h. FE-SEM OBSE RVATION FE-SEM (Qua nta 3D FEG, FEI Company) was used to observe the morphological charac- teristics and properties of PLO gel. Unlike conventional electron microscopy using a thermal emission gun, FE-SEM is a fi eld emission scanning electron microscope that Table II Independent Variable Range of Preliminary Experiment Independent variables Level Low (-1) Middle (0) High (+1) A: hydrogenated lecithin (wt%) 1.0 3.0 5.0 B: PEG-400 (wt%) 15.0 20.0 25.0 C: poloxamer 407 (wt%) 15.0 20.0 25.0 Figure 2. Preparation method of PLO gel. JOURNAL OF COSMETIC SCIENCE 330