218 JOURNAL OF COSMETIC SCIENCE 70 to 50 o,• 4o • 30 =o • 10 :-=- o -20 -30 1 Mp-1 I I 12 14 16 18 20 Carbon Chain Length Figure 4. Effect of carbon chain length on the transition temperature (ratio of unsaturation to saturation 1:1). Error bars indicate the standard error of the mean of three replicates. nents are significantly smaller than the slopes of the saturated components, which means that the increase in carbon chain length affects the saturated portion more than the unsaturated portion. EFFECT OF PERCENT SATURATED The effect of saturation (corresponding to Table IV) on the melting temperatures is -10 3:1 2:1 1:1 1:2 1:3 0:1 -50 -25 0 25 50 75 100 Temperature (øC) Figure 5. Thermogram showing the effect of percent saturated in the model sebum for carbon chain length 16. Numbers on the side of thermograms indicate the ratio of unsaturation to saturation.

DSC STUDIES OF SEBUM MODELS 219 shown in Figure 5. The transition temperatures are plotted versus the percent saturated in Figure 6. As the saturation increases (or unsaturation decreases), the temperatures of the unsaturated components (Mp-1 and Mp-2) decrease with a concurrent increase in the Mp-3 and Mp-4. Since the slope of Mp-3 is significantly higher than that of Mp-4, it would seem that the unsaturation seems to affect the wax ester portion of the model sebum more than the triglyceride and fatty acid portion of the mixture. It appears that Mp-1 and Mp-2 are affected to a lesser extent in terms of their melting point than both Mp-3 and Mp-4 (from slopes). As mentioned earlier, the presence of other substances decreases the melting point of the pure compounds. When there is more unsaturation than saturation, by the time the temperature is reached for the melting of the saturated compounds, some of the saturated portion dissolves in the already-melted unsaturated portion and their melting point decreases. The more the unsaturation, the more the dissolving and hence the higher decreases in the melting point. In these cases, the unsaturated portion acts as the solvent. When the percent of saturated fraction is greater, -eo -30 a Mp-1 20 40 60 80 % Saturated (w/w) 100 • 60 o • 55 • 50 o 45 = 35 '-' 30 ,• 25 20 Mp-4 • Mp-3 • 0 20 40 60 80 100 % Saturated (w/w) Figure 6. Effect of percent saturated on transition temperatures (a) Mp-1 and Mp-2 and (b) Mp-3 and Mp-4 for C-16. Error bars indicate the standard error of the mean of three replicates.