(383j) Arrested Coalescence of Emulsion Drops

Emulsions are the primary means of active delivery in many consumer products and their stability is a critical performance metric.  One key mechanism of emulsion instability is droplet coalescence, the collision and merging of two droplets into a single, larger one. Another type of droplet-droplet interaction is also possible in emulsions with colloids present: arrested coalescence.  When droplets containing particulate solids contact one another their coalescence can be arrested, before completion, by the colloidal microstructure that forms.  Interestingly, arrested coalescence is not always detrimental to a material’s stability; sometimes a beneficial gel structure is created.

Here we map the regimes of arrested coalescence behavior of individual drops as a function of solids fraction and relate the microstructural results to colloidal phase behavior.  A microscopic capillary technique is used to make in situ observations of the  arrested coalescence dynamics between two oil drops in water. Partitioning of colloidal particles either inside the oil droplet or at the oil-water interface is controlled using surfactants to alter the particle wettability.  Using measurements of the relevant interfacial parameters, we engineer the droplet interactions to optimize structuring even in large-scale processes.