Roughness gradient induced spontaneous motion of droplets on hydrophobic surfaces: A lattice Boltzmann study

TL;DR

This study uses lattice Boltzmann simulations to explore how stepwise changes in pillar density on hydrophobic surfaces induce droplet motion or arrest, revealing linear relationships between velocity, texture gradient, and surface tension.

Contribution

It demonstrates the influence of pillar density gradients on droplet dynamics and provides a simple predictive model validated by simulations.

Findings

Droplet velocity scales linearly with surface texture gradient.

Droplet velocity depends linearly on surface tension.

Different pillar arrangements can cause motion or arrest.

Abstract

The effect of a step wise change in the pillar density on the dynamics of droplets is investigated via three-dimensional lattice Boltzmann simulations. For the same pillar density gradient but different pillar arrangements, both motion over the gradient zone as well as complete arrest are observed. In the moving case, the droplet velocity scales approximately linearly with the texture gradient. A simple model is provided reproducing the observed linear behavior. The model also predicts a linear dependence of droplet velocity on surface tension. This prediction is clearly confirmed via our computer simulations for a wide range of surface tensions.