Related Experiment Video
Updated: Oct 21, 2026

Film Control to Study Contributions of Waves to Droplet Impact Dynamics on Thin Flowing Liquid Films
Published on: August 18, 2018
From singular jets to compound droplets: Viscosity and inertia control of immiscible drop-pool impact dynamics
Hyunji Lee1, Choongyeop Lee2, Hyungmin Park3
1Department of Mechanical Engineering, Seoul National University, Seoul, 08826, South Korea.
Hypothesis:
Secondary-droplet composition in immiscible drop-pool impact is hypothesized to be governed by the relative motion of the oil-air and oil-water interfaces formed at the tip and inside the jet, respectively. Increasing oil (droplet) viscosity should reduce this relative motion and favor compound oil-water droplets, while crown breakup may provide an additional high-inertia route to their formation.
Experiments:
Silicone-oil droplet (2.7-2.8 mm in diameter) with dynamic viscosity in the range of 0.49-96.3 mPa · s, impacts a deep-water pool at 1.6-4.4 m/s, covering Froude and Ohnesorge numbers of 99-727 and 0.003-0.4, respectively. High-speed shadowgraphy and tracer-particle visualization, with tracers dispersed only in the water phase, are used to track both interfaces and identify secondary-droplet composition.
Findings:
Based on jet morphology and secondary-droplet composition, four regimes were identified: (i) a short jet without pinch-off, (ii) a singular jet, (iii) an oil-dominated secondary-droplet regime, and (iv) a compound secondary-droplet regime. Following the inertia-driven crater, the subsequent collapse-to-jet transition was strongly affected by oil viscosity. Increasing viscosity limited the stretching of the oil-rich portion in the jet, resulting in the thick jet. This shifted the location of primary pinch-off from the internal interface (oil secondary droplet) to the water-containing lower portion of the jet (compound one). At sufficiently high impact inertia, crown breakup provided an additional route to compound-droplet formation. These new findings establish a direct link between the coupled kinematics of the oil-air and oil-water interfaces, pinch-off location, and secondary-droplet composition in immiscible impacts.
Related Concept Videos
Precipitate Formation and Particle Size Control
The obtained precipitate should be either a pure substance of known composition or easily converted to one by a simple process, such as ignition or drying. In addition, the precipitate should be insoluble and easily filterable. In general, filterability...
Free Jet
Viscosity
The SI unit of viscosity is...
Viscosity
Viscosity of Fluid
Surface Tension of Fluid
Surface tension varies with...

