Photomicroscopic Observation of Dispersion State of Droplets in Flowing Emulsion

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The viscosity of dilute emulsion with disperse phase of volume fraction φ=0.005–0.06 was measured, and the dispersion state of emulsion droplets under shear was observed with a photomicroscope. Oil components used were aromatic hydrocarbons, i.e., benzene, o-xylene, and toluene, and saturated hydrocarbons, i.e., cyclohexane, decaline, n-hexane, etc. As emulsifier, Arlacel 60 or Arlacel 83 was used for W/O type emulsion and Tween 20 for O/W type one. For the W/O type emulsions of aromatic hydrocarbon of low emulsifier concentration (0.2%), Einstein's equation could be applied to the viscosity at a high rate of shear in the range of φ below 0.02, in spite of the presence of aggregates of droplets in the flowing emulsion. When φ becomes 0.04–0.06, the deviation from Einstein's equation was large. In the case of higher emulsifier concentration (1%), the deviation from Einstein's equation was noticeable even for φ=0.01, when Arlacel 60 was used as stabilizer. The results may be brought about by the increase of effective volume fraction of disperse phase owing to the inclusion of continuous phase liquid in aggregates. In the case of W/O type emulsions of saturated hydrocarbon and O/W type ones, irrespective of the kind of oil phase liquid, the aggregates were completely redispersed into primary droplets at a high rate of shear, and Einstein's equation could be applied.
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