Fate of Nanobubbles Generated from CO2–Hydrate Dissociation: Coexistence with Nanodroplets—A Combined Investigation from Experiment and Molecular Dynamics Simulations

Abstract

The evolution of CO₂ nanobubbles generated by gas–hydrate dissociation is comprehensively studied in this research, employing a synergistic approach that combines laboratory experiments and molecular dynamics simulations. The results show that a higher concentration of nanobubbles can be observed in the early stages of hydrate dissociation, while smaller, thus-generated, nanobubbles are less stable and prefer to amalgamate into larger bubbles through coalescence or Ostwald ripening. From the high Laplace pressure inside some nanobubbles as well as their higher local densities, they may transform into nanodroplets by densification fluctuations. Thus, the dynamic coexistence of nanobubbles and -droplets is confirmed from both experimental and simulation measurements. The number and size of the nanobubbles in the system affects the interaction between water molecules and their movements so that the water molecules diffuse faster upon this condition. The water–water interactions become more pronounced in the presence of nanobubbles and the hydrogen bond network is better preserved in the bulk. This study provides new insights into the microscale mechanisms of gas–hydrate dissociation and highlights the complex interactions between nanobubbles/ -droplets, and the aqueous environment after CO₂–hydrate dissociation.