Dynamics of nanodroplets on topographically structured substrates

TL;DR

This study uses mesoscopic hydrodynamic equations to analyze how nanodroplets move near topographic steps on substrates, revealing dependence on system length scales, intermolecular forces, and the barrier effect of steps.

Contribution

It provides a detailed analysis of nanodroplet dynamics near substrate steps, highlighting the influence of length scales and intermolecular forces, which was not fully understood before.

Findings

Nanodroplet motion follows a power law relative to distance from the step.

Direction of motion depends on effective intermolecular forces and Hamaker constant.

Steps act as barriers preventing droplet crossing.

Abstract

Mesoscopic hydrodynamic equations are solved to investigate the dynamics of nanodroplets positioned near a topographic step of the supporting substrate. Our results show that the dynamics depends on the characteristic length scales of the system given by the height of the step and the size of the nanodroplets as well as on the constituting substances of both the nanodroplets and the substrate. The lateral motion of nanodroplets far from the step can be described well in terms of a power law of the distance from the step. In general the direction of the motion depends on the details of the effective laterally varying intermolecular forces. But for nanodroplets positioned far from the step it is solely given by the sign of the Hamaker constant of the system. Moreover, our study reveals that the steps always act as a barrier for transporting liquid droplets from one side of the step to the other.