Enhanced Condensation on Lubricant-Impregnated Nanotextured Surfaces

TLDR

Nanotextured superhydrophobic surfaces can shed liquid drops, but condensation inside the textures impales vapor pockets, pins droplets, and degrades droplet mobility and overall condensation performance. The study demonstrates that a hierarchical micro‑nanotexture combined with lubricant impregnation can dramatically reduce condensate pinning. By selecting a lubricant with a positive spreading coefficient relative to the solid and liquid phases, the lubricant cloaks condensate and, when it does not fully wet the solid, the nanotexture further mitigates pinning. On the engineered surface, 100‑µm condensate droplets move continuously at speeds several orders of magnitude higher than on identical superhydrophobic textures, creating a sweeping effect that clears the surface for fresh nucleation and enhances condensation.

Abstract

Nanotextured superhydrophobic surfaces have received significant attention due to their ability to easily shed liquid drops. However, water droplets have been shown to condense within the textures of superhydrophobic surfaces, impale the vapor pockets, and strongly pin to the surface. This results in poor droplet mobility and degrades condensation performance. In this paper, we show that pinning of condensate droplets can be drastically reduced by designing a hierarchical micro-nanoscale texture on a surface and impregnating it with an appropriate lubricant. The choice of lubricant must take into account the surface energies of all phases present. A lubricant will cloak the condensate and inhibit growth if the spreading coefficient is positive. If the lubricant does not fully wet the solid, we show how condensate–solid pinning can be reduced by proper implementation of nanotexture. On such a surface, condensate droplets as small as 100 μm become highly mobile and move continuously at speeds that are several orders of magnitude higher than those on identically textured superhydrophobic surfaces. This remarkable mobility produces a continuous sweeping effect that clears the surface for fresh nucleation and results in enhanced condensation.