Two coarsening mechanisms of emulsions are well established: droplet coalescence (fusion of two droplets) and Ostwald ripening (molecular exchange through the continuous phase). Here we demonstrate the existence of a third mechanism, contact ripening, which operates through molecular exchange upon droplets collisions. A contrast manipulated small angle neutron scattering experiment was performed to isolate contact ripening from coalescence and Ostwald ripening. The key parameters have been identified through a kinetic analysis using dynamic light scattering and monodisperse nanoemulsions. Contact ripening is accelerated by increasing the concentration of droplets but hindered by repulsions between droplets and highly hydrated cohesive films. These parameters can be tuned to control the magnitude of this exchange/coarsening mechanism, which is essential for both emulsion formulation and delivery of hydrophobic ingredients.

The project has been completed.

People: Kevin Roger, Ulf Olsson, Bernard Cabane (ESPCI, Paris), Ralf Schweins (ILL, Grenoble)

Contact person:Ulf Olsson