Dynamic Leidenfrost effect: relevant time- and length-scales

TL;DR

This study investigates the dynamic Leidenfrost effect during droplet impact on hot surfaces, revealing the critical time- and length-scales that determine when droplets levitate due to vapor generation.

Contribution

It provides new insights into the transitional wetting and levitation regimes by observing droplet dynamics at nanometer scales with high-speed imaging.

Findings

Identification of key time- and length-scales for droplet levitation

Observation of wetting/drying transition processes

Enhanced understanding of the dynamic Leidenfrost temperature

Abstract

When a liquid droplet impacts a hot solid surface, enough vapor may be generated under it as to prevent its contact with the solid. The minimum solid temperature for this so-called Leidenfrost effect to occur is termed the Leidenfrost temperature, or the dynamic Leidenfrost temperature when the droplet velocity is non-negligible. We observe the wetting/drying and the levitation dynamics of the droplet impacting on an (isothermal) smooth sapphire surface using high speed total internal reflection imaging, which enables us to observe the droplet base up to about 100 nm above the substrate surface. By this method we are able to reveal the processes responsible for the transitional regime between the fully wetting and the fully levitated droplet as the solid temperature increases, thus shedding light on the characteristic time- and length-scales setting the dynamic Leidenfrost temperature for droplet impact on an isothermal substrate.