Role of Nanostructure Coating Quality in Delay of Surface Flooding during Jumping Droplet Condensation

Vapor condensation is commonly observed in everyday life and routinely used in industry as an effective means of transferring heat. In industrial systems, condensed vapor typically forms a thin liquid film which is not desired due to the large thermal resistance to heat transfer; however, if the condensing surface is functionalized with a hydrophobic coating, the condensate forms discrete liquid droplets which shed at sizes approaching the capillary length and refresh the surface for re-nucleation, resulting in a 5--7x heat transfer improvement. Furthermore, when a micro- or nanostructured surface is functionalized, a superhydrophobic surface can be created on which small ($\approx $10-100 \textmu m) droplets coalesce and can spontaneously jump away from the surface due to release of excess surface energy; this jumping droplet mode of condensation has been shown to increase heat transfer by an additional 30 -- 40{\%}. However, at elevated supersaturations, nanostructured superhydrophobic surfaces can become flooded with condensate and form pinned droplets which cannot jump, thereby eliminating the desired heat transfer improvement. In this work, we experimentally demonstrated a delay in the supersaturation at which surface flooding occurs by reducing the hydrophobic coating defect density. This resulted in a lower proportion of structure unit cells occupied by condensate, which allowed higher droplet mobility and jumping at elevated supersaturation.