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

Ruri Hidema,Susan J Muller,Hiroshi Suzuki,Ryotaro Ohashi

doi:10.1063/5.0055436

Ruri Hidema, Susan J Muller + Show 2 more

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https://doi.org/10.1063/5.0055436

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Abstract

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.

Highlights

The processes of production and manipulation of droplets in microscale devices have attracted considerable research attention in the last two decades
We have focused on double emulsion production in a planar flow focusing device with triangle-shaped orifices
We present the definition of the capillary number that has been used in this study and characterize the flow regimes based on the capillary number

Summary

Introduction

The processes of production and manipulation of droplets in microscale devices have attracted considerable research attention in the last two decades. Microfluidic droplet formation has been intensively studied and shows potential for future applications, such as in chemical reactions in a confined space, particle production, synthesis of cell-like biomaterials, and encapsulation of biological molecules or drugs.[1–9] An important aspect to ensure for achieving uniform and stable droplets in droplet formation processes is the control of the fluid interface. To exploit the advantages of microscale processes, several types of microfluidic devices and techniques have been proposed previously.[4]. Flow focusing is a widespread microfluidic method for producing uniform droplets. The other is hydrodynamic flow focusing; in this case, the fluids meet at a cross-junction to produce droplets as a result of interface instabilities.[12,13]. Flow focusing is a promising technique for producing uniform droplets when the flow is stable and well-controlled. A trivial factor destabilizes the fluid interface, which prohibits the production of uniform droplets

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