Visualization Study of Oil-in-Water-in-Oil (O/W/O) Double Emulsion Formation in a Simple and Robust Co-Flowing...

A simple and robust co-flowing microfluidic device for double emulsion preparation is designed and assembled to visually study the double emulsion formation by the use of a microscope and high-speed camera. Using a visualization system, the transient processes of double emulsion formation in co-flowing stream are observed and recorded for a variety of flow rates. The effects of flow rates of each fluid on flow modes, drop sizes, and polydispersities are examined and analyzed. The results indicate that the detaching of the inner drops accelerates the detaching of the outer drops and speeds up the drop formation process of double emulsions. The manipulation of flow rates is capable to actively control the sizes of the inner and outer drops as well as the number of inner drops encapsulated. Without surface modification, the microfluidic device produces a variety of emulsions, including the single-core and multi-core O/W/O double emulsions as well as binary emulsions of single and double emulsions. The proposed co-flowing microfluidic device is highly desirable in producing double emulsions in an easy and cheap way.