On-demand Interfacial Coverage and Composition using Double Emulsion Templating

Emulsions are dispersions of an immiscible liquid into another liquid. We encounter them on daily basis, such as in food and personal care products. However, emulsions are thermodynamically unstable due to the high cost of the interface between the droplets and matrix fluid. For this reason, emulsions tend to coarsen over time by morphological processes such as coalescence and Ostwald ripening to reduce their interfacial energy. Therefore, surface active agents are necessary to improve the long term stability by lowering the interfacial energy. Due to the extremely high stability of particle-stabilized emulsions against coalescence and Ostwald ripening, Pickering emulsions have recently gained a renewed interest. Another advantage is their surfactant-free character, since surfactants often show adverse effects, in particular in cosmetic and pharmaceutical applications. Unfortunately, it is difficult to control the size and particle surface coverage in bulk emulsification methods. In contrast, in a microfluidic device one droplet is precisely fabricated at a time, which makes it possible to control the interfacial rheological properties of the coated droplets and to produce a very monodisperse emulsion. Due to the high precision, it is also possible to fabricate double, triple and even higher order emulsions with a certain size and number of encapsulated droplets with a high accuracy.

The overall goal of the research is the production of individual droplets with well-controlled interfacial rheological properties to study their direct effect on droplet deformation and coalescence in coalescence geometries in which a wide range of deformation/approaching speeds is possible for a single pair of droplets. This will give insight on the direct effect of the interfacial rheological properties on coalescence stability, allowing engineering guidelines for the selection or development of the optimally performing interfacial stabilizers.