Droplet fusion by the interplay of electric potential and converging–diverging geometry in micro‐channels

BACKGROUND Rapid and precise manipulation of droplets in microfluidic devices is in greater demand than ever. Droplet fusion and separation based on dielectrophoresis (DEP) in particular, commonly employed in a variety of biomedical operations, are studied extensively. Here, a full‐scale computational study is performed to understand the mechanism for the fusion of relatively small microdroplets. Based on the phase field theory, the droplet boundary is precisely tracked and a mathematical model including laminar flow, electrostatic field, and phase field is developed, while the DEP force acting on droplets is obtained by the Maxwell stress tensor (MST) method. RESULTS In this paper, a method of droplet fusion in converging–diverging micro‐channels is studied. The electric field strength is generated by applying electric potential on the boundaries of calculation domain. The size and position of electric potential will affect the droplet fusion. Moreover, the simulation results show that the converging–diverging channel geometry and the external electric field applied can effectively promote droplet fusion and that a smaller throat width and higher electric field intensity lead to more efficient droplet fusion. CONCLUSION The conclusion of this study provides theoretical support for droplet manipulation in micro‐channels. This study may provide a method for the design and optimization of droplet microfluidic chips, thus achieving the wide application of droplet technology in microfluidic chips. © 2020 Society of Chemical Industry (SCI)