Study of directional splitting characteristics of compound droplets containing solid core in Y-junction microchannel

In this study, we designed a microfluidic configuration incorporating with a directional channel perpendicular to the main channel before a Y-junction, enabling precise control over droplet splitting by adjusting the directional flow rate. Our experiments revealed four distinct flow regimes and the fitting formula accurately predicted the critical directional points in the flow regime map under different capillary numbers. Trajectory analysis of the solid cores demonstrated that their displacement within compound droplets is influenced by both the directional and main channel flow rates, and we proposed a theoretical model to accurately predict this displacement. Moreover, particle image velocimetry experiments are conducted to provide insights into the velocity field evolution across different flow regimes, highlighting the significant impact of flow rates on droplet deformation, splitting, and solid core movement. The results enhance the controllability of microfluidic systems and broaden their applicability in fields like biomedicine and chemical engineering.