Abstract
The effect of aging over 135 days on the rate of separation of oil from 50% liquid petrolatumce:inf>50% water emulsions with both 0.2 and 0.4% sodium dodecyl sulfate (based on the water) was determined in an ultracentrifuge at 25° and 39,460 r.p.m. The concentration of sodium dodecyl sulfate in the equilibrium aqueous phase was also determined. The stability of the emulsion with 0.2% sodium dodecyl sulfate decreased for the first 25 days and thereafter increased with time, with a qualitative change in the mode of loss of oil after 135 days. There was no change in the stability of the emulsion with 0.4% sodium dodecyl sulfate over the same time period. The results with the 0.2% sodium dodecyl sulfate emulsion can be rationalized in terms of an initial increase in drop size with an accompanying desorption of sodium dodecyl sulfate and a decrease in stability, followed by coverage of a greater fraction of the remaining oilce:inf>water interface by adsorbed sodium dodecyl sulfate from the more concentrated solution of sodium dodecyl sulfate resulting from the initial desorption.
Published Version
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