Capillary filling in drop merging: dynamics of the four-phase contact point

TL;DR

This paper investigates the unique dynamics of the four-phase contact point during immiscible drop merging, revealing its scaling behavior and proposing a force balance model that aligns with experimental observations.

Contribution

It introduces the first detailed study of the four-phase contact point dynamics in immiscible drop merging and presents a predictive model for its behavior.

Findings

The four-phase contact point propagates with a t^{0.5} scaling in various scenarios.

A force balance model accurately predicts the contact point dynamics.

Experimental data confirms the proposed scaling laws.

Abstract

The merging of immiscible drops differs significantly from the merging of miscible drops due to the formation of a liquid-liquid interface between drops. The immiscibility requires the formation of a four-phase contact point, where the drops, the gas and the substrate meet. We show that this point has its own unique dynamics, never studied beforehand. For very different scenarios, the propagation distance of this point follows scales with time like t^{0.5}. A model balancing the driving and dissipative forces agrees with our experiments.