Understanding droplet bridging in ionic liquid-based Pickering emulsions.

We have studied the unique bridging behavior of solid-stabilized oil-in-ionic liquid (IL) and water-in-ionic liquid emulsions with respect to particle concentration, particle size, and droplet phase using a confocal laser scanning microscope. The emulsions exhibited three morphology regimes: (1) single, sparingly covered droplets, (2) bridged clusters of droplets, and (3) fully covered droplets. The degree of bridging was directly proportional to the total potential bridging area which can be determined from the particle size and concentration. This type of emulsion diverges from much of the conventional wisdom of oil-water Pickering emulsions regarding the particle self-assembly onto droplet interfaces and liquid film stability. While the focus here is the bridging regime, we also report interesting observations, specifically, the deformed oil droplets and the transport of excess solid particles into the water droplets, in the fully covered droplet regime. The work identified new self-assembled particle structure and morphology in solid-stabilized emulsions.