336 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Q:::: 12_ z I 0 4 6 I I I EMULSIFIER CONC. (% W/W) Figure 4. Median particle diameter of emulsion droplets at different emulsifier concentrations. No polymer added. Storage time: [] 1 day, + 60 days. number correlated with visual observation of the emulsions. Emulsions containing up to 1% emulsifier were much more opaque in appearance than emulsions containing higher concentrations of emulsifier. AGING EFFECTS AT ROOM TEMPERATURE No oil separation was observed in any emulsion stored at room temperature for more than a year with the exception of some containing high sodium sulfate concentrations. These will be discussed below. Particle size distributions were obtained on each emulsion just after manufacture and about two months later. Additional measurements were performed on selected emul- sions at additional intervals. Several emulsions (containing no polymer, 0.2% xanthan gum, and 0.4% xanthan gum) were reinvestigated 308 and 427 days after manufacture. Particle size data of representative emulsions are collected in Table II. In no case was a significant change noted with time. Several of the emulsions containing 5% emulsifier exhibited an increase in the ratio of particles above 20 I.•m to the total count. With most of these emulsions, the number of particles decreased during the same storage period (two months). These data are sug-

EMULSION STABILIZATION BY GUMS 337 70 , 6o o o o x o -- o 5o 4o 50- 20- 10 0 0 2 4 6 EMULSIFIER CONC. (• W/W) Figure 5. Effect of emulsifier concentration on total number of particles in emulsions containing no polymer. gestive of coalescence, so that the percentage of larger particles is increased at the expense of the smaller ones. As would be expected, the process is accompanied by a decrease in the total number of particles. Viscosity data for the emulsions are summarized in Tables III and IV. The viscosity of emulsions containing no polymer was too low to be measured accurately under the Table II Effect of Xanthan Gum on Median Particle Size at 1% (w/w) Emulsifier Concentration Emulsifier Conc. (% w/w) Median Particle Size (micrometer) Xanthan Gum Conc. (% w/w) Aging (days) 0 0.1 0.2 0.3 0.4 1.0 1 4.30 4.30 4.40 4.15 4.10 28 4.35 4.40 4.60 -- -- 56 4.65 4.65 4.85 4.85 4.80 214 4.50 4.65 4.80 4.85 4.65 308 4.35 4.60 -- 4.60 427 4.30 4.50 -- 4.40