Dual residence time for droplet to coalesce with liquid surface

TL;DR

This paper investigates the dual residence times of droplets coalescing with a liquid surface, revealing how parameters like viscosity and radius influence the occurrence of two distinct delay durations.

Contribution

It presents the first detailed analysis of dual residence times, combining experimental observations with theoretical models to explain their dependence on physical parameters.

Findings

Dual residence times exhibit two peaks in their distribution.

Higher viscosity and smaller radius suppress the longer residence time peak.

Physical models explain the influence of droplet properties on coalescence delay.

Abstract

When droplets approach a liquid surface, they have a tendency to merge in order to minimize surface energy. However, under certain conditions, they can exhibit a phenomenon called coalescence delay, where they remain separate for tens of milliseconds. This duration is known as the residence time or the non-coalescence time. Surprisingly, under identical parameters and initial conditions, the residence time for water droplets is not a constant value but exhibits dual peaks in its distribution. In this paper, we present the observation of the dual residence times through rigorous statistical analysis and investigate the quantitative variations in residence time by manipulating parameters such as droplet height, radius, and viscosity. Theoretical models and physical arguments are provided to explain their effects, particularly why a large viscosity or/and a small radius is detrimental to the appearance of the longer residence time peak.