Effect of the initial concentration of emulsifying agents on the ultracentrifugal stability of oil-in-water emulsions

The rate of loss of oil from 50% Nujol-50% water emulsions stabilized with varying concentrations of Tween 20 or Triton X-100, and from 50% olive oil-50% water emulsions stabilized with sodium dodecyl sulfate (SDS), was determined by ultracentrifugation at 39,460 rpm. In all cases the ultracentrifugal stability increased with increasing initial concentration of emulsifier, although, unlike the behavior of Nujol-water-SDS emulsions, the rate of separation of oil decreased with time. The quantity of olive oil separated after a given time of centrifugation decreased linearly with increasing concentration of SDS, reaching zero at a concentration of SDS somewhat below the critical micelle concentration, and at adsorption of SDS corresponding to only about half the saturation capacity. The ultracentrifugal stability of Nujol emulsions with Tween 20 or Triton X-100 continued to increase slowly with increasing concentration of emulsifier, even at concentrations far greater than the critical micelle concentration.