Evaporation of Water Nanodroplets on Heated Surfaces: Does Nano Matter?

Luis Ruiz Pestana, Teresa Head-Gordon

Research output: Contribution to journalArticlepeer-review

Abstract

While experiments and continuum models have provided a relatively good understanding of the evaporation of macroscopic water droplets, elucidating how sessile nanodroplets evaporate is an open question critical for advancing nanotechnological applications where nanodroplets can play an essential role. Here, using molecular dynamics simulations, we find that evaporating nanodroplets, in contrast to their macroscopic counterparts, are not always in thermal equilibrium with the substrate and that the vapor concentration on the nanodroplet surface does not reach a steady state. As a result, the evaporative behavior of nanodroplets is significantly different. Regardless of hydrophobicity, nanodroplets do not follow conventional evaporation modes but instead exhibit dynamic wetting behavior characterized by huge, non-equilibrium, isovolumetric fluctuations in the contact angle and contact radius. For hydrophilic nanodroplets, the evaporation rate, controlled by the vapor concentration, decays exponentially over time. Hydrophobic nanodroplets follow stretched exponential kinetics arising from the slower thermalization with the substrate. The evaporative half-lifetime of the nanodroplets is directly related to the thermalization time scale and therefore increases monotonically with the hydrophobicity of the substrate. Finally, the evaporative flux profile along the nanodroplet surface is highly nonuniform but does not diverge at the contact line as the macroscopic continuum models predict.

Original languageEnglish (US)
Pages (from-to)3563-3572
Number of pages10
JournalACS Nano
Volume16
Issue number3
DOIs
StatePublished - Mar 22 2022
Externally publishedYes

Keywords

  • evaporation
  • kinetics
  • molecular dynamics
  • nanodroplet
  • non-equilibrium
  • water

ASJC Scopus subject areas

  • Materials Science(all)
  • Engineering(all)
  • Physics and Astronomy(all)

Fingerprint

Dive into the research topics of 'Evaporation of Water Nanodroplets on Heated Surfaces: Does Nano Matter?'. Together they form a unique fingerprint.

Cite this