The coalescence of liquid droplets

Droplet coalescence is essential from inkjet printing to aerosols in spraying. In all such processes the drop size distribution is of key importance, which is not only governed by drop formation, but also to a large part by coalescence. Despite the large body of research on drop coalescence, there remains a discrepancy among experiments, theories, and computational models, particularly in the very early moments following the initial contact of two drops. The understanding that has emerged is that coalescence has two regimes: inertial regime and viscous regime. However, recent work [1] demonstrates a third regime so-called inertially-limited-viscous (ILV) regime from which coalescence should begin. Here, we numerically and experimentally investigate the coalescence dynamics using a new geometry, drop-bath, instead of the classic drop-drop. This allows us to probe the coalescence dynamics at very early stage (~ 1 μs). We show that the deformation of the bath surface significantly modifies the dynamics due to the jump into contact [2]. We also develop a simple crossover scaling to describe the viscous-to-inertial transition in coalescence [3].

[1] J.D. Paulsen, J.C. Burton, S. R. Nagel, S. Appathurai, M. T. Harris, and O. A. Basaran. The inexorable resistance of inertia determines the initial regime of drop coalescence. PNAS, 109(18), pp.6857-6861 (2012).
[2] A. Deblais, K. Xie, P. Lewin-Jones, D. Aarts, M. A. Herrada, J. Eggers, J. E. Sprittles, D. Bonn. Early stages of drop coalescence (draft)
[3] K. Xie, M. Corpart, A. Deblais, D. Bonn. Drop-drop coalescence: a simple crossover function between inertial and viscous dynamics (under review).