How Do Emulsions Evaporate?

Evaporation rates of water and oil from creamed oil-in-water emulsions have been measured under
conditions of controlled gas flow. The continuous water phases of the emulsions evaporate at rates equal to that for pure water under the same conditions. The evaporation rates of dispersed oil drops are retarded, relative to nonemulsified oil, by factors ranging from 1 to 20. Rates for different emulsified oils are all consistent with a mechanism in which the oil drops remain separated from the vapor phase by a thin water
film at the emulsion surface. Oil transport from the drops to the vapor occurs by diffusion of dissolved oil across this water film. Measured evaporation rates show good agreement with model calculations based on this proposed mechanism.