Speaker
Description
Due to spontaneous local density fluctuations, transient bubbles can be observed in liquids, even in the stable phase. This is even more true for metastable liquids, and, in this case, it is obviously highly relevant for the liquid-to-vapor transition, since the nucleation of the new phase will occur through bubble growth. In the context of liquids confined in porous media, the question of the influence of the walls is raised. How do fluid-walls interactions affect the dynamics of density fluctuations, and by way of consequence the probability of occurrence of transient bubbles? This is an important issue to understand cavitation in porous materials [1,2].
Unfortunately, these transient bubbles are too small to be experimentally observable. On the other hand, molecular simulations are reliable enough, at the involved time and space scales, to provide quantitative insights. One major quantity is the distribution $p(s)$ of the size $s$ of the bubbles, which can be acquired over time during a long simulation run [3]. This distribution is identical to the one that would be determined from a single molecular configuration, provided that it is large enough to contain a large number of transient bubbles. Our objective is to provide a clear understanding of this distribution $p(s)$, in connection with the free energy of formation of a bubble $W(s)$. In particular, $p(s)$ is expected to be proportional to the Boltzmann factor exp$[-W(s)/kT]$ [4]. In the capillarity approximation, $W(s)$ is generally written in terms of surface and volume contributions. It is shown that this approximation is not fully compatible with simulation results, and that it is required to introduce an additional contribution proportional to the bubble radius [5]. Furthermore, the proportionality factor explicitly depends on the chosen quantity to define the size (e.g. radius or volume). It is observed that this factor is constant if the bubble size is measured by its radius, while a factor $v^{-2/3}$ has to be introduced when the bubble size is defined by its volume $v$. These results are expected to impact the calculation of nucleation barriers [6], and, consequently, the predictions of the classical nucleation theory. In the context of liquids confined in nanopores, we will also explore the influence of the fluid-wall interactions on the distribution $p(s)$ and the nucleation barrier.
| References | [1] M. Bossert, A. Grosman, I. Trimaille, F. Souris, V. Doebele, A. Benoit-Gonin, L. Cagnon, P. Spathis, P.-E. Wolf and E. Rolley, Evaporation Process in Porous Silicon: Cavitation vs Pore Blocking. Langmuir 37, 14419–14428 (2021). [2] M. Bossert, I. Trimaille, L. Cagnon, B. Chabaud, C. Gueneau, P. Spathis, P. E. Wolf and E. Rolley, Surface tension of cavitation bubbles. Proc. Natl. Acad. Sci. U. S. A. 120, e2300499120 (2023). [3] J. Puibasset, Are nucleation bubbles in a liquid all independent?, J. Mol. Liq. 387, 122638 (2023). [4] H. Reiss; R. K. Bowles, Some fundamental statistical mechanical relations concerning physical clusters of interest to nucleation theory. J. Chem. Phys. 111, 7501-7504 (1999). [5] J. Puibasset, Molecular-sized bubbles in a liquid: Free energy of formation beyond the capillarity approximation. J. Chem. Phys. 163, 034110 (2025). [6] J. Puibasset, A General Relation between the Largest Nucleus and All Nuclei Distributions for Free Energy Calculations, J. Chem. Phys. 157, 191102 (2022). |
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| Country | France |
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