We study the effect of multi-drop environment on the deformation, break-up and coalescence phenomena in concentrated emulsions. A novel technique was developed to observe the fundamental thin film drainage and deformation processes at the level of an individual drop in a ‘crowded' emulsion.

The experiments focused on analyzing the dynamics of two micron-sized polydimethylsiloxane (PDMS) drops in a suspension of monodispersed polymethylmethacrylate (PMMA) particles. The PMMA particles were refractive index matched with the suspending fluid to render the image analysis of the two PDMS drops possible. The system was subjected to a planar hyperbolic flow field and the drainage time was measured in head-on and glancing collision configurations as a function of various parameters like the capillary number, viscosity ratio, particle size and concentration. The effects associated with the ‘crowding' of particles were isolated by comparing the data obtained with suspensions against that for two drops in a particle-free suspending fluid.

The many-body interactions due to particles affect the thin film dynamics by influencing the flow field universally as well as by producing short-ranged localized effects. The global effects such as the increased suspension viscosity and flow segregation of particles act to modify the flow. The local effects are more subtle and tend to be statistical in nature, like small-scale fluctuations in film shape due the varying particle-based temperature field and steric changes in global drop deformation.