Dynamical Model for Chemically Driven Running Droplets

TL;DR

This paper introduces a dynamical model for chemically driven running droplets, explaining their motion through coupled equations that account for chemical reactions affecting wettability, and identifies two regimes of droplet movement.

Contribution

It develops a coupled evolution model for liquid film thickness and adsorbate density, revealing two distinct regimes of droplet motion driven by chemical reactions.

Findings

Identification of reaction-limited and saturated regimes

Explanation of experimental observations of droplet velocities

Model predicts velocity dependence on reaction rates and droplet size

Abstract

We propose coupled evolution equations for the thickness of a liquid film and the density of an adsorbate layer on a partially wetting solid substrate. Therein, running droplets are studied assuming a chemical reaction underneath the droplets that induces a wettability gradient on the substrate and provides the driving force for droplet motion. Two different regimes for moving droplets -- reaction-limited and saturated regime -- are described. They correspond to increasing and decreasing velocities with increasing reaction rates and droplet sizes, respectively. The existence of the two regimes offers a natural explanation of prior experimental observations.