Generation of double emulsions from commercial single-emulsion microfluidic chips: a quality-control study

Microfluidic devices can form monodisperse double emulsions, but the fabrication steps are complicated and require specialized equipment. Recently, a method to convert single emulsions into double emulsions using vortex mixers has been proposed. Using this method, we demonstrate the production of double emulsions using commercially available single-emulsion microfluidic chips. We characterize the effect of vortex speed, vortex duration and the number of vortex/flick cycles on the average diameter and coefficient of variation of the double emulsions. Using fluorescent nanoparticles as tracers, we show that droplet breakup occurs during the second emulsification (using the vortex), but did not observe any fusion between the cores of double emulsion droplets. We also found that some inverted double emulsion droplets containing the outer water phase in their core were produced during vortex emulsification. Finally, while commercial chips only exist with a finite range of channel size that sets the monodispersed emulsion droplet radius, we show that the double-emulsion droplet radius can be adjusted using osmotic pumping. Our method is simple, available and user-friendly for biomedical researchers.

Automated summary

This paper presents a simple, convenient, and user-friendly method for converting single emulsions into double emulsions using vortex mixers. The authors studied the effects of vortex speed, vortex duration, and the number of vortex/flick cycles on the properties of the double emulsions. Interesting phenomena, such as droplet breakup and the production of inverted double emulsion droplets, were observed.