12 JOURNAL OF COSMETIC SCIENCE Sample at room temperature diameter pm Figure 3. Diagram of size droplets in Figure 1. MICROSCOPY STUDY Photographs were taken of samples kept at room temperature, at 40øC, and at 60øC over time. Figure 1 shows the sample prepared at room temperature, and Figure 2 the one prepared at elevated temperature. It is apparent that there is little difference in the Sample at elevated temperature .:-' .• ." ?: .'"'•.' :•'."r4 .t "5 •':,: '" .. 3 4 $ 6 7 8 9 10 , 11 12 13 Diameter pm Figure 4. Diagram of size droplets in Figure 2.

SILICONE-BASED EMULSION GELS 13 Table I Comparison of Statistical Parameters for Room-Temperature and Elevated-Temperature Formulas Statistical parameters Room-temperature Elevated-temperature formula formula Number of droplets (N) Average diameter by number (Dn, lam) Average diameter by weight (Dw) Average diameter by volume (Dv) Average diameter by area (Ds) Average diameter (Dz) Polydispersive index (PDI) Standard deviation (SD) Geometric standard deviation (GSD) Coefficient of variation % (CV) 231 357 2.81 2.81 7.O9 7.6 3.96 4.O9 3.35 3.41 8.27 8.89 2.52 2.7 1.82 1.93 1.76 1.77 64.81 68.42 droplet size between these two preparations. Figures 3 and 4 present the results from the determination of the droplet size in both photographs, applying a statistical process (see Table I). Note that the average diameter is around 2.8 !am, with a slightly higher polydispersive index for the heated sample. The percentage of the coefficient of variation is also higher in sample 2. All these values support the conclusions drawn from the organoleptic analysis of the preparations, in that the differences between the two meth- ods are minimal, but slightly favor the formulation manufactured at room temperature. After being subjected to extreme temperature conditions (60øC for over a week) and to centrifugation (10,000 rpm for 30 min), slight coalescence can be observed, with drop- lets tending to clump and occasionally increasing in size (Figure 5). & . Figure 5. The sample after centrifugation.