Two recipes for repelling hot water

TL;DR

This paper presents two structural surface designs that effectively repel hot water by preventing condensation and water bridge formation, overcoming the challenge of maintaining repellency at high temperatures.

Contribution

It introduces two novel surface microtexture recipes—nanometric and larger features—that enable hot water repellency by different mechanisms.

Findings

Both nanometric and larger features reflect hot water at various impact velocities.

Nanometric features minimize water bridge formation due to miniaturization.

Larger features slow condensation kinetics, preventing water-solid bridges.

Abstract

Although a hydrophobic microtexture at a solid surface most often reflects rain owing to the presence of entrapped air within the texture, it is much more challenging to repel hot water. As it contacts a colder material, hot water generates condensation within the cavities at the solid surface, which eventually builds bridges between the substrate and the water, and thus destroys repellency. Here we show that both "small" (~100 nm) and "large" (~10 \mu m) model features do reflect hot drops at any drop temperature and in the whole range of explored impact velocities. Hence, we can define two structural recipes for repelling hot water: drops on nanometric features hardly stick owing to the miniaturization of water bridges, whereas kinetics of condensation in large features is too slow to connect the liquid to the solid at impact.