Dropwise condensation on superhydrophobic surfaces with two-tier roughness

TLDR

Dropwise condensation can enhance heat transfer by an order of magnitude compared to film condensation, and on micro‑nanostructured surfaces condensate drops prefer the thermodynamically stable Cassie state, making superhydrophobicity an ideal but previously unreported promoter of continuous dropwise condensation. This study demonstrates continuous dropwise condensation on a superhydrophobic surface composed of short carbon nanotubes on micromachined posts, a two‑tier texture that mimics lotus leaves. The surface is fabricated by depositing short carbon nanotubes on micromachined posts and applying a hexadecanethiol coating to preserve superhydrophobicity during and after condensation, enabling rapid drop removal. The resulting surface maintains superhydrophobicity throughout condensation and facilitates rapid drop removal, confirming continuous dropwise condensation.

Abstract

Dropwise condensation can enhance heat transfer by an order of magnitude compared to film condensation. Superhydrophobicity appears ideal to promote continued dropwise condensation which requires rapid removal of condensate drops; however, such promotion has not been reported on engineered surfaces. This letter reports continuous dropwise condensation on a superhydrophobic surface with short carbon nanotubes deposited on micromachined posts, a two-tier texture mimicking lotus leaves. On such micro-/nanostructured surfaces, the condensate drops prefer the Cassie state which is thermodynamically more stable than the Wenzel state. With a hexadecanethiol coating, superhydrophobicity is retained during and after condensation and rapid drop removal is enabled.