Effects of channel geometry and physicochemical properties of solutions on stable double emulsion production in planar microfluidic devices having triangular orifices

The planar microfluidic devices for producing double emulsions are beneficial in terms of accuracy and facility in fabrication. However, factors such as the flow rates, interfacial tensions, viscosities, channel geometry, and wettability of the devices affect the stability of the double emulsion production. In this study, we have focused on double emulsion production in a planar flow focusing device with triangle-shaped orifices. The local velocity in the channel can be controlled by modifying the channel design. Here, we have used two types of microfluidic devices with orifices and junctions of different shapes, denoted as mc-A and mc-B. By controlling the orifice angles and the width of the junctions, the stable flow regimes characterized in a capillary number space were expanded, and the production efficiency was increased. The effects of interfacial tensions of the sample solutions on the stability of double emulsion production were also examined. The double emulsions produced under stable conditions were highly uniform, and the diameter of the produced emulsions was well defined by the capillary numbers. However, the diameter of the double emulsions was mainly affected by the size of the orifice.