Pressure-driven liquid-liquid separation in Y-shaped microfluidic junctions

- Formation of two phase flow regimes was examined experimentally and numerically.
- Loading back-pressure caused separation of immiscible liquids in microchannel.
- An interfacial pressure balance model was proposed.

On-chip phase separation of multiphase microflows at the divergence point of Y-shaped microfluidic junctions is an effective way for integrating continuous microstructured devices. In this study, flow pattern maps of various solvent pairs based on the volumetric flow rates of both phases have been drawn experimentally and compared with numerical prediction to investigate the effective domain for which complete phase separation occurred. Furthermore, sufficient separation of aqueous and organic phases at the end of the microchannel was achieved by controlling the pressure difference at the liquid-liquid interface via loading back-pressure on the organic phase. A mathematical model based on interfacial pressure balance was derived. It was found that organic phase outlet tube should be kept between the upper and lower values calculated from the model. Only narrow discrepancy between the model and experimental observation can be seen in using viscous organic solvents.