Droplet formation dynamics under perpendicular and head-on dispersed phase configuration in a microfluidic T-junction

Controlled and efficient droplet formation in microfluidic devices is highly desired in chemical and biological analysis, drug delivery, micro-reactor, and material synthesis, among others. Achieving desired droplet morphologies often depends on fine-tuning of fluid thermophysical properties and flow dynamics. Furthermore, microchannel geometry modification offers an efficient way of exploring controlled droplet generation in microfluidic devices. This work focuses on probing the influence of dispersed phase configurations on the droplet generation dynamics in T-junction microfluidic devices. Specifically, we investigate the dynamics of droplet formation in two different configurations involving “perpendicular” (θ=90°) and “head-on” (θ=180°) interactions of dispersed phase and continuous phase fluids at the junction. We perform comprehensive experiments to investigate the role of flow parameters such as capillary number (Ca), and flow rate ratio (φ) on droplet generation in both configurations. Our experiments show that the head on geometry has increased droplet formation time compared to perpendicular geometry, which can be attributed to a lower interfacial drag on the dispersed phase fluid. We substantiate this hypothesis by performing micro particle image velocimetry (μ-PIV) experiments on both configurations. Furthermore, we show that the head-on geometry has higher vorticity inside the evolving dispersed phase droplet. This increased vorticity prevents interface deformation, slowing down the necking, and results in an increased dispersed film length in head-on configuration.