Symmetric and Asymmetric Coalescence of Drops on a Substrate

TL;DR

This paper investigates the coalescence dynamics of viscous drops on a substrate, revealing self-similar bridge evolution and providing a universal description that matches experiments without adjustable parameters.

Contribution

It introduces a theoretical framework using similarity solutions of lubrication equations to describe asymmetric coalescence of sessile drops, validated by experiments.

Findings

Bridge grows linearly in time

Universal shape described by similarity solutions

Strong dependence on contact angles

Abstract

The coalescence of viscous drops on a substrate is studied experimentally and theoretically. We consider cases where the drops can have different contact angles, leading to a very asymmetric coalescence process. Side view experiments reveal that the "bridge" connecting the drops evolves with self-similar dynamics, providing a new perspective on the coalescence of sessile drops. We show that the universal shape of the bridge is accurately described by similarity solutions of the one-dimensional lubrication equation. Our theory predicts a bridge that grows linearly in time and stresses the strong dependence on the contact angles. Without any adjustable parameters, we find quantitative agreement with all experimental observations.