Driving Droplet by Scale Effect on Microstructured Hydrophobic Surfaces

TL;DR

This paper introduces a novel droplet transportation method on microstructured hydrophobic surfaces driven by scale effects, supported by experimental and theoretical analysis, revealing new insights into topology-wetting relationships.

Contribution

It presents a new mechanism for droplet movement based on scale effects and line tension, differing from traditional methods, with experimental validation and theoretical explanation.

Findings

Droplets move unidirectionally from small to large micro-pillars.

Dynamic contact angle decreases with increasing pillar scale.

The scale effect can be harnessed for microfluidic device design.

Abstract

A new type of water droplet transportation on microstructured hydrophobic surface is proposed and investigated experimentally and theoretically - water droplet could be driven by scale effect which is different from the traditional methods. Gradient microstructured hydrophobic surface is fabricated in which the area fraction is kept constant, but the scales of the micro-pillars are monotonic changed. When additional water or horizontal vibration is applied, the original water droplet could move unidirectionally to the direction from the small scale to the large scale to decrease its total surface energy. A new mechanism based on line tension model could be used to explain this phenomenon. It is also found that dynamic contact angle decreases with increasing the scale of the micro-pillars along the moving direction. These new findings will deepen our understanding of the relationship between topology and wetting properties, and could be very helpful to design liquid droplet transportation device in microfluidic systems.