Structure of concentrated oil-in-water Pickering emulsions

Abstract

Following the structural changes in unstable Pickering emulsions is difficult due to the emulsion turbidity. We studied droplet packing in concentrated oil-in-water emulsions stabilized by silanised silica particles using confocal fluorescence microscopy to image thin sections of the emulsions. As the volume fraction of the drops approaches close packing, they deform into polyhedral shapes and flattened areas of contact between droplets appear. We show that the increase in the average number of nearest neighbours of a drop is a power law function of the drop volume fraction, consistent with theoretical predictions. At the volume fraction where the emulsions start to break down, ϕ = 0.88, there is a jump in drop elongation and thus in the number of drops in contact with each other. Drops increase in size, with some forming shapes that resemble an intermediate stage of the coalescence process. A few large drops grow more than most. A key finding is that the rigidity of the droplet surfaces controls the destabilization mechanism.