Microfluidic generation of monodisperse ultra-low interfacial tension oil droplets in waterElectronic supplementary information (ESI) available: Video of a micrometer-sized oil droplet in water near the microemulsion phase transition showing thermal capillary waves at the droplet interface. See DOI: 10.1039/c4ra14967j

We present a novel microfluidic approach for the generation of monodisperse oil droplets in water with interfacial tensions of the order of 1 μN m −1 . Using an oil-in-water emulsion containing the surfactant aerosol OT, heptane, water and sodium chloride under conditions close to the microemulsion phase transition, we actively controlled the surface tension at the liquid-liquid interface within the microfluidic device in order to produce monodisperse droplets. These droplets exhibited high levels of stability with respect to rupture and coalescence rates. Confirmation that the resultant emulsions were in the ultra-low tension regime was determined using real space detection of thermally-induced capillary waves at the droplet interface. A microfluidic platform was used to generate a monodisperse oil-in-water emulsion, whose final interfacial tension was actively lowered to ultra-low values.