Single condensation droplet self-ejection from divergent structures with uniform wettability

TL;DR

This study demonstrates the self-ejection of individual condensation droplets from uniformly hydrophobic divergent microstructures, revealing new insights into droplet dynamics and potential applications in anti-icing and water harvesting.

Contribution

It introduces a novel approach using uniformly wetted microcones to achieve droplet self-ejection without detachment from pinning sites, supported by experimental and theoretical analysis.

Findings

Droplets self-eject after growth and self-propulsion cycles.

Uniform wettability microstructures enable high-efficiency droplet ejection.

Potential for improved anti-icing and water harvesting technologies.

Abstract

Coalescence-jumping of condensation droplets is widely studied for anti-icing, condensation heat transfer, water harvesting and self-cleaning. Another phenomenon that is arousing interest for potential enhancements is the individual droplet self-ejection. However, whether it is possible from divergent structures without detachment from pinning sites remains unexplored. Here we investigate the self-ejection of individual droplets from divergent, uniformly hydrophobic structures. We designed, fabricated and tested arrays of nanostructured truncated microcones arranged in a square pattern. The dynamics of the single condensation droplet is revealed with high speed microscopy: it self-ejects after cycles of growth and self-propulsion between four cones. Adopting the conical pore for simplicity, we modelled the slow iso-pressure growth phases and the surface energy release-driven rapid transients enabled once a dynamic configuration is reached. In addition to easier fabrication, microcones with uniform wettability have the potential to allow self-ejection of almost all the droplets with a precise size while maintaining mechanical resistance and thus promising great improvements in a plethora of applications.