Thermodynamic Stability of Nanobubbles

TL;DR

This paper explains the surprising stability of nanobubbles by identifying two non-classical mechanisms: decreasing surface tension with supersaturation and stabilization of immobilized hemispherical bubbles, challenging classical nucleation theory.

Contribution

It introduces a novel explanation for nanobubble stability involving non-classical effects and demonstrates stability conditions for immobilized hemispherical bubbles.

Findings

Surface tension decreases with supersaturation.

Immobilized hemispherical bubbles are stable.

Total entropy is maximized at the critical radius.

Abstract

The observed stability of nanobubbles contradicts the well-known result in classical nucleation theory, that the critical radius is both microscopic and thermodynamically unstable. Here nanoscopic stability is shown to be the combined result of two non-classical mechanisms. It is shown that the surface tension decreases with increasing supersaturation, and that this gives a nanoscopic critical radius. Whilst neither a free spherical bubble nor a hemispherical bubble mobile on an hydrophobic surface are stable, it is shown that an immobilized hemispherical bubble with a pinned contact rim is stable and that the total entropy is a maximum at the critical radius.