Description
Compound droplets have attracted significant attention in recent years due to their wide-ranging applications in targeted drug delivery, nanoparticle synthesis, encapsulation technologies, and biomedical diagnostics. Their ability to encapsulate multiple functional materials within a single droplet enables controlled release, enhanced stability, and multifunctional performance, making them highly desirable in advanced microfluidic systems. Microfluidic technology has emerged as a powerful and versatile platform for the controlled generation of compound droplets, offering precise manipulation of flow conditions, fluid properties, and interfacial phenomena to tailor droplet size, morphology, and dynamics [1]. Among various microfluidic configurations, co-flow microchannels are particularly advantageous due to their simple geometry, stable operation, and capability to produce highly monodisperse droplets.
In the present work, a co-flow microfluidic device is numerically modeled to investigate the formation and transport dynamics of compound droplets using a Computational Fluid Dynamics (CFD) solver. The system consists of three immiscible phases, wherein a non-Newtonian fluid is employed as the droplet-forming phase to closely represent realistic biofluids and polymeric solutions commonly encountered in drug delivery applications [2]. The interface dynamics between the three immiscible fluids are captured using the Coupled Level Set and Volume of Fluid (CLSVOF) method [3]. A comprehensive parametric study is performed to elucidate the effects of key operating parameters, including flow rate ratios, viscosity ratios, and interfacial tension, on the size, shape, velocity, and generation frequency of compound droplets. The results reveal that systematic variation of flow conditions provides effective control over droplet size and shape. Furthermore, non-dimensional scaling correlations are developed to relate the droplet characteristics to governing parameters, such as the Reynolds number, Weber number, and capillary number, offering a predictive capability for device design. Distinct flow regimes, namely squeezing, dripping, and jetting, are identified and mapped within the operational parameter space. Overall, the findings offer fundamental insights into the mechanisms of compound droplet formation and identify key controlling factors for precise droplet manipulation. The results provide valuable insights for optimizing microfluidic systems aimed at critical mineral extraction, drug delivery, and other biomedical applications requiring controlled encapsulation and transport of complex fluids.
References
[1] Cerdeira, Ana TS, et al. "Review on microbubbles and microdroplets flowing through microfluidic geometrical elements." Micromachines 11.2 (2020): 201.
[2] Chen, Qi, et al. "Pressure-driven microfluidic droplet formation in Newtonian and shear-thinning fluids in glass flow-focusing microchannels." Int. J. Multiph. Flow 140 (2021): 103648.
[3] Jammula, Manohar, and Somasekhara Goud Sontti. "High-throughput controlled droplets generation through a flow-focusing microchannel in shear-thinning fluids." Phys. Fluids 37.7 (2025).