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Microfluidic Flow-Focusing Systems for Alginate Microcapsule Preparation: Tuning Droplet Size and Frequency

Authors :

Meisam Akbari laleh¹ Yasaman Pahlevanzadeh² Mina Shafiei³ Javad Rahbar shahrouzi⁴

1- دانشگاه صنعتی امیرکبیر 2- دانشگاه صنعتی شریف 3- دانشگاه صنعتی سهند 4- دانشگاه صنعتی سهند

Keywords :

Microfluidics،Droplet generation،Flow-focusing،Alginate microdroplets،Level-Set method،Junction angle،Two-phase flow،Numerical simulation

Abstract :

Microencapsulation is an efficient method for protecting unstable compounds in chemical environments and has wide applications in medicine and tissue engineering. In this study, the formation of alginate microgels in a microfluidic flow-focusing device was numerically simulated using COMSOL Multiphysics 6.3 based on the Level-Set method. The results demonstrated that wall contact angle, flow rate of the phases, and the junction angle of the channels (30°, 60°, 90°, and 120°) significantly affect droplet size and generation frequency. Superhydrophobic channels (θ = 150°) facilitated stable W/O droplet formation, while hydrophilic walls failed to produce droplets. Increasing the dispersed phase flow rate (Qd) led to larger droplets and plug flow, whereas increasing the continuous phase flow rate (Qc) reduced droplet size due to enhanced shear stress. Overall, the simulation results indicate that the junction angle directly governs the balance between viscous shear forces and interfacial tension. Narrower angles favor shear-dominated breakup with smaller, more monodisperse droplets, whereas wider angles shift the mechanism toward pressure-driven pinch-off, producing larger droplets with lower throughput. Therefore, the channel intersection angle serves as an effective design parameter for tuning droplet size distribution and generation rate in microfluidic systems.