Strain-induced droplet retraction memory in a pickering emulsion.

We studied the deformation and relaxation of a water droplet covered with polystyrene latex particles (diameter ca. 200 nm) and embedded in an immiscible fluid after a large strain jump. We show that the presence of the solid particles at the droplet interface slows down the retraction kinetics in comparison with a pure water droplet and induces flow singularity not observed with pure water droplets. The terminal relaxation time of the retraction process, defined as the characteristic time required for the droplet to relax to its spherical equilibrium shape, increases linearly with the applied strain. This result implies a memory effect induced by the presence of solid particles at the droplet interface in a solid-stabilized or Pickering emulsion.