Spontaneous emulsification at the water/oil interface

Emulsification processes usually require the application of external energy to enlarge the interfacial area between both media. We study here a case where practically no external energy is required to form an emulsion, i.e., it is produced spontaneously when both liquids are put in contact in the presence of one surfactant species. We report the observation and measurements of the kinetics of the spontaneous formation and growth of water droplets at the water/oil + lipophilic surfactant interface. The droplets can reach sizes up to several microns, and their growth is found to obey a power law for a range of the surfactant concentration.

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► Water droplets are spontaneously produced at the water/dodecane interface.
► Water droplets attached to the interface grow at the expense of the aqueous phase.
► The droplets’ radius follows a power law for a range of surfactant concentration.