Motion of nanodroplets near chemical heterogeneities

TL;DR

This paper studies how nanodroplets move near chemical boundaries on a substrate, revealing that their motion depends on long-range dispersion forces and can differ from intuitive expectations based on wettability alone.

Contribution

It introduces a model showing that nanodroplet dynamics near chemical heterogeneities are influenced by Hamaker constants, not just contact angles, highlighting a novel mechanism for droplet motion.

Findings

Droplets perceive the other side of the step at a distance due to dispersion forces.

Droplet motion depends on Hamaker constants, not only contact angles.

Motion can be directed towards less wettable areas, contrary to intuition.

Abstract

We investigate the dynamics of nanoscale droplets in the vicinity of chemical steps which separate parts of a substrate with different wettabilities. Due to long-ranged dispersion forces, nanodroplets positioned on one side of the step perceive the different character of the other side even at some distances from the step, leading to a dynamic response. The direction of the ensuing motion of such droplets does not only depend on the difference between the equilibrium contact angles on these two parts but in particular on the difference between the corresponding Hamaker constants. Therefore the motion is not necessarily directed towards the more wettable side and can also be different from that of droplets which span the step.