Non‐monotonic jet pinch‐off induced by droplet impact on immiscible liquids

Abstract Droplet impact on immiscible liquids can generate a central jet whose pinch‐off behavior plays a crucial role in many advanced interfacial processes, including spray cooling, liquid metal–water interaction, interfacial reaction enhancement, and flexible interfacial deposition. Here, we investigate the jet dynamics and pinch‐off mechanism following a water droplet impact on an immiscible liquid. High‐speed photography was employed to comprehensively capture the formation, growth, and eventual pinch‐off process of the central jet. The influence of Weber number, Ohnesorge number, and dimensionless film thickness on the central jet behavior was analyzed. Two distinct central jet regimes were identified: a continuous jet and a pinch‐off jet depending on whether central jet breakup occurs. It is found that, regardless of the liquid‐film viscosity, the critical Weber number—defined as the Weber number at which central jet pinch‐off occurs—reaches a maximum at a dimensionless film thickness of 1.5. Furthermore, a semi‐empirical correlation combining a single exponential function with a Lorentzian‐type function is proposed to characterize the non‐monotonic dependence of the maximum jet height on the dimensionless film thickness, thereby providing a unified description of the jet dynamics across different liquid surfaces.