Ice-bridging frustration by self-ejection of single droplets results in superior anti-frosting surfaces

TL;DR

This study introduces microstructured, hydrophobic surfaces that enable self-ejection of condensation droplets, effectively preventing ice-bridge formation and achieving superior anti-frosting performance beyond current passive solutions.

Contribution

The paper demonstrates how microcone arrays with nanostructures promote droplet self-ejection, reducing frost propagation and simplifying manufacturing without pinning sites.

Findings

Frost velocity reduced below 0.5 μm/s, halving current limits.

Self-ejection efficiency peaks on cones with sharp tips.

Microstructures enable precise control of droplet size and distribution.

Abstract

Surfaces capable of delaying the frosting passively and facilitating its removal are highly desirable in fields where ice introduces inefficiencies and risks. Coalescence jumping, enabled by highly hydrophobic surfaces, is already exploited to slow down the frosting but it is insufficient to completely eliminate the propagation by ice-bridging. We show how the self-ejection of single condensation droplets can frustrate the ice bridges of all the condensation droplets leading to a frost velocity lower than 0.5 um/s thus dropping below the current limits of passive surfaces by a factor of at least 2. Arrays of truncated microcones, covered by uniformly hydrophobic nanostructures, enable individual condensation droplets to growth and self-propel towards the top of the microstructures and to self-eject once a precise volume is reached. The independency of self-ejection on the neighbour droplets allows a precise control on the droplets' size and distance distributions and the ice-bridging frustration. The most performant microstructures tend to cones with a sharp tip on which the percentage of self-ejection is maximum. Looking towards applications, tapered microstructures allow maximising the percentage of self-ejecting drops while maintaining a certain mechanical strength. Further, it is shown that inserted pinning sites are not essential, which greatly facilitates manufacturing.