Surface Curvature-Induced Directional Movement of Water Droplets

TL;DR

This study demonstrates how nanoscale water droplets move directionally on curved graphene surfaces due to van der Waals interactions, independent of wettability, with potential applications in surface water management.

Contribution

It reveals the curvature-induced directional movement of water droplets on graphene surfaces through molecular dynamics simulations, highlighting the role of van der Waals forces and wettability effects.

Findings

Water droplets move toward larger ends on outer surfaces and smaller ends on inner surfaces of graphene cones.

Movement direction is independent of surface wettability, whether hydrophobic or hydrophilic.

Higher motion speeds are observed on hydrophilic surfaces.

Abstract

Here we report a surface curvature-induced directional movement phenomenon, based on molecular dynamics simulations, that a nanoscale water droplet at the outer surface of a graphene cone always spontaneously moves toward the larger end of the cone, and at the inner surface toward the smaller end. The analysis on the van der Waals interaction potential between a single water molecule and a curved graphene surface reveals that the curvature with its gradient does generate the driving force resulting in the above directional motion. Furthermore, we found that the direction of the above movement is independent of the wettability, namely is regardless of either hydrophobic or hydrophilic of the surface. However, the latter surface is in general leading to higher motion speed than the former. The above results provide a basis for a better understanding of many reported observations, and helping design of curved surfaces with desired directional surface water transportation.