What is it about?
When using molecular dynamics simulations to study the emergence, stability and longevity of bulk gas-filled NanoBubbles (bNBs) in supersaturated gas-liquid solutions, a simple and fair question usually arise: if those bNBs are characterized with high internal-pressure due to their small radii, why do they persist to exist in the simulation domain? The article is about answering this question, which is focused on the case of weak and supersaturated gas-liquid solutions. Although this seems to be contradictory to the basic and fundamental laws of solubility and Young-Laplace, we find that, in fact, it is not. Under periodic boundary conditions, molecular dynamics simulation best resemble closed and finite-volume systems, and we rely on relevant thermodynamic theories to explain the stability of bNBs. In essence, there exists a bNB size and concentration of dissolved gas in the liquid solution (background supersaturation) such that the thermodynamically-preferential mass-transfer direction is still from the liquid solution towards the bNB, i.e., it will grow. For micro-bubbles, Ward and Tucker theoretically and experimentally investigated and proved this hypothesis a few decades ago.
Featured Image
Photo by Marcel Strauß on Unsplash
Why is it important?
Our approach and findings shed light on three important aspects. Firstly, it explains bNB stability and its thermodynamic irreversibility using kinetic considerations and an ideal irreversibility criterion. Moreover, we inspire from stochastic and dynamics of complex systems methods to identify such a definite (yet nonunique) state of thermodynamic irreversibility, starting from homogeneous state of the system. Secondly, it gives relevance, in the context of computer experiments, and supports theoretical thermodynamic perturbation approaches that were common a few decades ago. Thirdly, it links the bNB stability to the background supersaturation (chemical equilibrium), where the effect of system size on the simulations is unambiguous. The stabilization mechanism of the bNB turns out to be no more than the hypothesized shielding mechanism, where background supersaturation and existence of many bNBs in a finite volume enhance its stability.
Perspectives
We attempt to interpret observations in computer experiments in closed and finite-volume systems by relying on relevant theories. Indeed, we find consistency and suggest that an interrelation between chemical equilibrium and domain size can be established. This article will be followed by another article to justify the thermodynamic irreversibility using thermodynamic considerations, i.e., estimation bNB pressure, volume, gas solubility in the liquid, etc.
Abdulrahman S. Al-Awad
Read the Original
This page is a summary of: Stochastic computer experiments of the thermodynamic irreversibility of bulk nanobubbles in supersaturated and weak gas–liquid solutions, The Journal of Chemical Physics, July 2024, American Institute of Physics,
DOI: 10.1063/5.0204665.
You can read the full text:
Contributors
The following have contributed to this page
