| Fine particles, which are readily adsorbed at fluid-fluid interfaces, are used as stabilizers in emulsion technology as they form barriers on the drops' surfaces and prevent adjacent drops from coalescing with one another. In applications, however, demulsification is often as important as the emulsion process itself, and techniques capable of merging drops are sought to reverse the process.;In this thesis, we propose a new method to destabilize particle-stabilized emulsions, also referred to as Pickering emulsions. Our technique, which consists of applying an external electric field, is demonstrated experimentally by studying water drops in decane and silicone oil drops in corn oil, and using various types of particles. Experiments and simulations show that the externally applied electric field has two effects: (i) the drops elongate in the direction of the electric field, (ii) the local particle density varies on the drops' surfaces due to the dielectrophoretic (DEP) force acting on the particles. It is shown that the latter is the dominant factor in the destabilization process. Although there should be no electrostatic forces acting on neutral particles in a uniform electric field, the presence of the drop introduces some non-uniformity in the electric field intensity which is responsible for particle motions along the drops' surfaces. Particles migrate either to the poles or the equator of the drops, depending on the electrical properties of the particles, the surrounding fluid and the drops' fluid. As particles move, particle-free openings form on the drops' surfaces, thus allowing adjacent drops to merge. This process takes place even if the particles are fully packed on the drops' surfaces as the drops elongate under the action of the electric field and particles get ejected from the clustering areas due to a buckling phenomenon.;The success of the method, however, depends on the values of certain dimensionless parameters; specifically, the ratio of the work done by the dielectrophoretic force must be larger than the work done by the buoyant force. Moreover, drops do not coalesce through the regions where particles locally cluster, whether those are gathered at the poles or at the equator of the drops. |
