Controlling condensation and frost growth with chemical micropatterns.

Jonathan B Boreyko,Scott T Retterer,Kevin R Murphy,Saurabh Nath,Ryan R Hansen,C Patrick Collier

doi:10.1038/srep19131

Jonathan B Boreyko, Scott T Retterer + Show 4 more

Open Access

https://doi.org/10.1038/srep19131

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Abstract

In-plane frost growth on chilled hydrophobic surfaces is an inter-droplet phenomenon, where frozen droplets harvest water from neighboring supercooled liquid droplets to grow ice bridges that propagate across the surface in a chain reaction. To date, no surface has been able to passively prevent the in-plane growth of ice bridges across the population of supercooled condensate. Here, we demonstrate that when the separation between adjacent nucleation sites for supercooled condensate is properly controlled with chemical micropatterns prior to freezing, inter-droplet ice bridging can be slowed and even halted entirely. Since the edge-to-edge separation between adjacent supercooled droplets decreases with growth time, deliberately triggering an early freezing event to minimize the size of nascent condensation was also necessary. These findings reveal that inter-droplet frost growth can be passively suppressed by designing surfaces to spatially control nucleation sites and by temporally controlling the onset of freezing events.

Highlights

Frost inevitably forms on any subfreezing surface whose temperature is beneath the dew point
It was observed that even when supercooled condensate was continually removed from a superhydrophobic surface via coalescence-induced jumping before heterogeneous nucleation occurred, frost still grew over the surface[21]
No surface has been able to completely stop the inter-droplet growth of frost when a freezing event occurs near the population of supercooled condensate[24,28,29,30,31]; typically ice bridges connect for nearly every droplet on smooth hydrophobic surfaces and for approximately 1/3 of droplets on jumping-droplet superhydrophobic surfaces[21]

Summary

Introduction

Frost inevitably forms on any subfreezing surface whose temperature is beneath the dew point. Due to heterogeneous nucleation (typically at edge defects where jumping did not occur), at which point the frozen droplet harvested water from nearby liquid droplets, growing ice bridges that connected across the forming condensate in an unstoppable chain reaction[21,24]. This source-sink vapor interaction between an evaporating liquid droplet and a bridging frozen droplet is most likely due to the higher water vapor pressure over liquid water compared to frozen water[25,26,27]. To date there have been no reports using chemically patterned surfaces to characterize the spatial distribution of condensation or the related dynamics of inter-droplet frost growth

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Conclusion