Unexpected Suppression of Leidenfrost Phenomenon on Superhydrophobic Surfaces

TL;DR

This study demonstrates that microtextured superhydrophobic surfaces with doubly reentrant pillars can elevate the Leidenfrost temperature for water, enabling superhydrophobicity without suppressing vapor layer formation, which benefits thermal energy applications.

Contribution

It reveals how microtexture and surface chemistry can be engineered to maintain high Leidenfrost temperatures on superhydrophobic surfaces, a novel approach to improve heat transfer efficiency.

Findings

Leidenfrost temperature exceeds that on hydrophilic surfaces.

Microtextured surfaces enhance heat transfer by ~300% at 200°C.

Superhydrophobicity can be achieved without suppressing vapor layer formation.

Abstract

The Leidenfrost phenomenon entails the levitation of a liquid droplet over a superheated surface, cushioned by its vapor layer. For water, superhydrophobic surfaces are believed to suppress the Leidenfrost point ($\it{T}$$_{\rm L}$)-the temperature at which this phenomenon occurs. The vapor film obstructs boiling heat transfer in heat exchangers, thereby compromising energy efficiency and safety. Thus, it is desirable to realize superhydrophobicity without suppressing $\it{T}$$_{\rm L}$. Here we demonstrate that the $\it{T}$$_{\rm L}$ of water on microtextured superhydrophobic surfaces comprising doubly reentrant pillars (DRPs) can exceed those on hydrophilic and even superhydrophilic surfaces. We disentangle the contributions of microtexture, heat transfer, and surface chemistry on $\it{T}$$_{\rm L}$ and reveal how superhydrophobicity can be realized without suppressing $\it{T}$$_{\rm L}$. For instance, silica surfaces with DRPs facilitate ~300% greater heat transfer to water droplets at 200$^{\circ}$C in comparison with silica surfaces coated with perfluorinated-nanoparticles. Thus, superhydrophobic surfaces could be harnessed for energy efficient thermal machinery.