Controlled W/O/W double emulsification in 3-D PDMS micro-channels

This paper presents the development of three-dimensional PDMS microfluidic devices that are capable of generating water-in-oil-in-water double-emulsions in a controlled manner. Native PDMS micro-channels are employed to direct the three independently driven W/O/W phases throughout the emulsification process. In addition to fluid flow-rates and channel geometries, surfactants are also employed to stabilize the two oil-water interfaces and the outer water-PDMS interface. In the prototype demonstration, two-level SU-8 molds were fabricated to duplicate PDMS structures, which were bonded irreversibly to form 3-D micro-channels. Dripping was intentionally induced to generate uniform double emulsions with oleic acid as the aqueous phase. It was found that the overall and core diameters of the resulting double-emulsions could be adjusted independently, mainly by varying the outer and inner water flow-rates, respectively. As such, the presented double-emulsification scheme could potentially realize the controllability on emulsion structure and size distribution, which is desired for various biological and pharmaceutical applications.