Growth Dynamics and Gas Transport Mechanism of Nanobubbles in Graphene Liquid Cells

TL;DR

This study visualizes nanobubbles in water encapsulated by graphene using in situ ultrahigh vacuum TEM, revealing their growth mechanisms, stability factors, and unique gas transport properties at the nanoscale.

Contribution

First direct visualization of nanobubbles in liquid phase with TEM, uncovering growth dynamics, stability criteria, and unique gas transport mechanisms at the nanoscale.

Findings

Nanobubbles can be visualized in liquid using UHV-TEM.

Two growth mechanisms identified: Ostwald ripening and coalescing.

Gas transport at the nanobubble interface is free from dissolution.

Abstract

Formation, evolution, and vanishing of bubbles are common phenomena in our nature, which can be easily observed in boiling or falling waters, carbonated drinks, gas-forming electrochemical reactions, etc. However, the morphology and the growth dynamics of the bubbles at nanoscale have not been fully investigated owing to the lack of proper imaging tools that can visualize nanoscale objects in liquid phase. Here we demonstrate, for the first time, that the nanobubbles in water encapsulated by graphene membrane can be visualized by in situ ultrahigh vacuum transmission electron microscopy (UHV-TEM), showing the critical radius of nanobubbles determining its unusual long-term stability as well as two distinct growth mechanisms of merging nanobubbles (Ostwald ripening and coalescing) depending on their relative sizes. Interestingly, the gas transport through ultrathin water membranes at nanobubble interface is free from dissolution, which is clearly different from conventional gas transport that includes condensation, transmission and evaporation. Our finding is expected to provide a deeper insight to understand unusual chemical, biological and environmental phenomena where nanoscale gas-state is involved.