Confinement-Induced Alteration of Morphologies of Oil-Water Emulsions

Reversible alteration between different emulsion morphologies like core-shell and Janus is conventionally triggered by altering the interfacial energy between different phases. In contrast, here, we show that the morphology of dispersed droplets can be changed also when the emulsion is sufficiently confined between two parallel plates. In particular, we use three immiscible phases: silicone oil, paraffin oil, and aqueous solution of surface-active agents like agarose, sodium dodecylsulfate, dioctyl sodium sulfosuccinate, and cetyl trimethylammonium bromide to generate oil-in-water emulsions consisting of complex morphologies of the dispersed droplets. In the unconfined state, the core-shell drops appear with paraffin oil at the core and silicone oil at the shell. However, the morphology of oil droplets changes to Janus when the emulsion is confined between two parallel plates. We have shown that the meniscus of the continuous phase that forms between the parallel plates alters the pressure field in the emulsion and the total energy of the system, which trigger such morphological transition.