Comment on Levitation and Self-Organization of Liquid Microdroplets over Dry Heated Substrates

TL;DR

This paper critically examines a recent model explaining microdroplet levitation over heated surfaces, arguing that the original interpretation of the evaporation-driven Stefan flow mechanism is incorrect and proposing an alternative understanding.

Contribution

The authors challenge the existing model of droplet levitation, providing a different interpretation of the experimental observations and emphasizing the need for revised theoretical explanations.

Findings

The original Stefan flow model does not fully explain droplet levitation.

Alternative mechanisms may be responsible for observed microdroplet behavior.

Reinterpretation of experimental data suggests different underlying physics.

Abstract

In a recent letter [1], Zaitsev et al. report observations of evaporating water micro-droplets over a heated solid substrate and suggest a model for the mechanisms of both droplet levitation and inter-droplet interaction. According to their model, the reflection of the Stefan flow (due to droplet evaporation) off the substrate is the mechanism of levitation, while the same Stefan flow also results in droplet repulsion preventing them from merging. They further apply their model to explain the levitation of droplets over a liquid surface and suggest the h/R~R^-3/2 dependency for the droplet radius R vs. the height of its center above the surface, h. While there is no doubt that the experimentally observed phenomenon is of interest, here we show that the observations should be interpreted differently.