Inertial coalescence of a liquid drop surrounded by viscous liquid*

Coalescence of liquid drops is a phenomenon familiar in everyday life. In recent years, the dynamics of coalescence of liquid drops has been actively explored. Many groups have focused on the bridge formed between drops and revealed its growing dynamics such as viscous and inertial regimes. The coalescence where drops are surrounded by another liquid was also studied [1], and it was concluded that regardless of the viscosity ratio of the surrounding liquid to the droplet liquid, early neck dynamics is always governed by the viscosity of the drop [2].

Here, we performed an experiment similar to [1] but with the viscosity contrast reversed (the drop viscosity is lower than the surrounding liquid) by using a high-speed camera and a microscope lens. As a result, we found the velocity of growing neck in the present case is governed by inertia, which we reported at the last march meeting. This time, we report a different analysis to reinforce the previous arguments for the inertial dynamics, negating the possible effects of viscosity.

[1] Yokota, Okumura, PNAS, 108 (2011) 6337

[2] Paulsen, et al., Nat. Common., 5 3182 (2014)