The inexorable resistance of inertia determines the initial regime of drop coalescence

TL;DR

This paper uncovers a previously overlooked initial regime in drop coalescence dynamics, showing that inertia and viscosity influence the process from the very start, leading to a new phase diagram.

Contribution

It introduces a third initial regime in drop coalescence, supported by experiments and simulations, expanding the traditional viscous-inertial understanding.

Findings

Identification of a third initial regime in coalescence

Development of a new coalescence phase diagram

Experimental and simulation validation of the regime

Abstract

Drop coalescence is central to diverse processes involving dispersions of drops in industrial, engineering and scientific realms. During coalescence, two drops first touch and then merge as the liquid neck connecting them grows from initially microscopic scales to a size comparable to the drop diameters. The curvature of the interface is infinite at the point where the drops first make contact, and the flows that ensue as the two drops coalesce are intimately coupled to this singularity in the dynamics. Conventionally, this process has been thought to have just two dynamical regimes: a viscous and an inertial regime with a crossover region between them. We use experiments and simulations to reveal that a third regime, one that describes the initial dynamics of coalescence for all drop viscosities, has been missed. An argument based on force balance allows the construction of a new coalescence phase diagram.