A macroscopic model for sessile droplet evaporation on a flat surface

TL;DR

This paper introduces a simplified macroscopic model for sessile droplet evaporation that captures shape relaxation, evaporation dynamics, and contact line pinning, providing insights into how initial conditions and pinning influence evaporation time.

Contribution

The paper presents a new surface free energy-based relaxation model that simplifies the complex physics of droplet evaporation, including shape dynamics and pinning effects.

Findings

Shape relaxation impacts droplet lifetime.

Evaporation time depends on initial contact angle.

Contact line pinning significantly alters evaporation dynamics.

Abstract

The evaporation of sessile droplets on a flat surface involves a complex interplay between phase change, diffusion, advection and surface forces. In an attempt to significantly reduce the complexity of the problem and to make it manageable, we propose a simple model hinged on a surface free energy-based relaxation dynamics of the droplet shape, a diffusive evaporation model and a contact line pinning mechanism governed by a yield stress. Our model reproduces the known dynamics of droplet shape relaxation and of droplet evaporation, both in the absence and in the presence of contact line pinning. We show that shape relaxation during evaporation significantly affects the lifetime of a drop. We find that the dependence of the evaporation time on the initial contact angle is a function of the competition between the shape relaxation and evaporation, and is strongly affected by any contact line pinning.