Statics and dynamics of a cylindrical droplet under an external body force

TL;DR

This study uses Molecular Dynamics simulations to analyze how cylindrical droplets move under external forces, revealing how size and contact angle influence velocity and dissipation mechanisms, with analytical predictions matching simulation results.

Contribution

The paper provides a detailed analysis of droplet motion under external forces, introducing an analytical model that predicts velocity scaling with droplet size and slip length, validated by simulations.

Findings

Small droplets' velocity dominated by substrate friction

Large droplets' velocity scales linearly with size due to internal viscous dissipation

Analytical predictions agree well with simulation data

Abstract

We study the rolling and sliding motion of droplets on a corrugated substrate by Molecular Dynamics simulations. Droplets are driven by an external body force (gravity) and we investigate the velocity profile and dissipation mechanisms in the steady state. The cylindrical geometry allows us to consider a large range of droplet sizes. The velocity of small droplets with a large contact angle is dominated by the friction at the substrate and the velocity of the center of mass scales like the square root of the droplet size. For large droplets or small contact angles, however, viscous dissipation of the flow inside the volume of the droplet dictates the center of mass velocity that scales linearly with the size. We derive a simple analytical description predicting the dependence of the center of mass velocity on droplet size and the slip length at the substrate. In the limit of vanishing droplet velocity we quantitatively compare our simulation results to the predictions and good agreement without adjustable parameters is found.