The effect of viscosity ratio on drop pinch-off dynamics in two-fluid flow

Abstract Drop pinch-off draws a lot of interest from scientists and engineers because of widely practical applications as well as the fascinating mechanism of finite-time singularities and self-similar behavior. This work experimentally investigates the effect of viscosity ratio on the local pinch-off mechanism of liquid drops in both air and viscous fluids, with a high-speed camera. The results show that for 56 ≤ λ ≤ 6.3 × 103 and 0.009 ≤ λ ≤ 0.061, drop pinch-off exhibits self-similar profile which is asymmetric and conical away from hmin. Drop pinch-off in air with low viscosity ratios shows either in inertial regime (I) or transition from inertial to viscous regime (I→V). But the kinetics undergoes the inertial regime (I) to inertial-viscous regime (IV) through an intermediate viscous regime (V) when the viscosity ratio becomes larger. Drop pinch-off in viscous fluids displays the transition from inertial to viscous regime (I→V). These results agree well with Eggers’s universal solution until it becomes unstable and the previous literature. The viscosity ratio indeed affects the drop pinch-off dynamics as well as interface deformation. Our experiments enrich the understanding of the interaction between the internal and external fluids on drop pinch-off behavior near the singularity point.