Partial coalescence of drops at liquid interfaces

Reference

Blanchette, F., Bigioni, T., Nature 2 (2006).

Summary

Figure 1. Different colors represent different rotation velocities.

Figure 2.

Coalescence occurs when two separate masses of teh same fluid are brought into contact; to minimize surface energy, they combine into a single larger mass. However, this does not always occur when a drop of fluid comes into contact with a large reservoir of the same fluid. Sometimes, the drop partially coalesces, "pinches off" in the process of merging, and leaves behind a smaller droplet. The authors study the mechanism of this effect.

The authors deposited a liquid onto an identical liquid in air and filmed the process with a high-speed camera. The results are shown in Figure 1. As shown, the drop comes into contact and forms a smaller daughter droplet. The shape of the droplet was numerically simulated by solving the Navier-Stokes equations, including surface tension as a force on the localized interface. The simulation shapes matched well with the experimental results as shown in Figure 1. The authors ruled out static Rayleigh-Plateau instability as a cause for the pinch-off by modifying simulation parameters.