(85e) Exploring Multiphase Viscous Drop Impact With a Bulk Fluid

Exploring Multiphase Viscous Drop Impact with a Bulk Fluid

Miscible fluid systems are all around us from the mixture of water and dish soap in the kitchen to the dissolution of oxygen into blood.  Building our intuition about how miscible and immiscible fluid systems differ can significantly further our understanding of fluid mechanics.

We have developed an experiment to explore how a droplet impacts a bulk fluid interface.  A drop of dense, viscous fluid is ejected from a syringe, free falling into a bath of water.  A high-speed video is captured by triggering a laser photo diode system.  These liquid-liquid drop impact systems can be inherently complex due to the time dependent interfacial tension between the two phases.  Their interactions can produce a variety of unique shapes and morphologies including toroids, liquid columns, and captured bubbles.   We aim to understand the conditions under which these various regimes form and the physics governing their formation.

One particularly interesting regime is the "free-surface pendant drop."  Under certain conditions, drops will partially wet the bath surface, residing on top of the bath despite the drops greater density.  Interfacial tension between the drop and the bath reduces, as the drop dissolves into the bath, and the drop is driven down into the bath once gravity overcomes the interfacial tension.  Between the surface of the bath and the bulk of the downward driven drop, a liquid column is formed.  The liquid columns formed by these "free-surface pendant drops," as well as many other regimes, could have a variety of practical applications in industry.